TSS

ASM Thermal Spray Society An Affiliate Society of ASM International ®

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August 2006 Volume 1 • Issue 2

Your Thermal Spray Information Partner

I N T E R N A T I O N A L

Thermal Spray & Surface Engineering

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T H E O F F I C I A L N E W S L E T T E R O F T H E A S M T H E R M A L S P R AY S O C I E T Y

State of the Society Industry News Successful Consultant/Client Relationships Winning Alternative to Hard Chrome Plating C ITS 6 200 nt Eve rage e Cov

OSHA Hexavalent Chromium Regulation

www.asminternational.org/tss

August 2006 • Volume 1 • Issue 2

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The Hybrid Spray System P.S. Mohanty, D. Kosikowski, and J. Stanisic High speed camera photo of the HVOF/Arc hybrid gun during mode I operation.

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How to Characterize a Thermal Spray Coating Using Electron Microscropy Doug Puerta

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Spray Shop: Focus on Monitor Coatings A Winning Alternative to Hard Chrome In Deep Bore Applications P. Ruggiero and Marc Froning

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OSHA Hexavalent Chromium Regulation Daryl Crawmer

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Successful Consultant/Client Relationships R.C. Tucker, Jr.

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Better Performance of Plasma Thermal Spray Ronald J. Molz, Richard J. McCullough, and Torsten Wintergerste

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Editor Christopher Berndt Managing Editor Mary Anne Fleming Art Director Barbara L. Brody Production Manager Joanne Miller Associate Publisher Lana Shapowal Sales East Coast/Eastern Canada Mike Sellaroli Columbus, Ohio tel: 614/268-5260; email: [email protected] Midwest/West Coast/Western Canada Lana Shapowal Materials Park, Ohio tel: 440/338-5151, ext. 5647 email: [email protected] Thermal Spray Society Executive Committee Richard Knight, President Christopher C. Berndt, Past President Peter Hanneforth, Vice President William J. Lenling, Secretary/Treasurer Thomas S. Passek, Executive Director About the cover

P. Georgieva, R. Thorpe, A. Yanski, and S. Seal 100MXC nanostructured coating shows higher density and better properties than the conventional 95MXC coating.

Wire arc processing from a TAFA 8860 Arc Spray gun during atomization evaluation trials, property of Praxair Surface Technologies and Tafa Incorporated. See the article “Nanocomposite Materials: An Innovative Turnover for the Wire Arc Spraying Technology” by P. Georgieva, R. Thorpe, A. Yanski, and S. Seal, beginning on page 18.

Thermal Spray Celebrates Centennial Anniversary at ITSC 2006

International Thermal Spray & Surface EngineeringTM is published quarterly by ASM International®, 9639 Kinsman Road, Materials Park, OH 44073; tel: 440/338-5151; www.asminternational.org. Vol. 1, No. 2. Copyright© 2006 by ASM International®. All rights reserved.

Nanocomposite Materials: An Innovative Turnover for the Wire Arc Spraying Technology

Peter Hanneforth

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Editorial Industry News International Updates Members Corner JTST Highlights

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The acceptance and publication of manuscripts in International Thermal Spray & Surface Engineering does not imply that the editors or ASM International® accepts, approves, or endorses the data, opinions, and conclusions of the authors. Although manuscripts published in International Thermal Spray & Surface Engineering are intended to have archival significance, author’s data and interpretations are frequently insufficient to be directly translatable to specific design, production, testing, or performance applications without independent examination and verification of their applicability and suitability by professionally qualified personnel. iTSSe

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STATE OF THE SOCIETY GUEST EDITORIAL

he Thermal Spray Society (TSS) has grown and prospered since the last International Thermal Spray Conference & Exposition (ITSC) was held in the U.S. in Orlando in 2003. Membership since 2004 has grown, with a total membership of 1,500 expected by the end of this year. TSS’s financial history is also positive. Revenues have stayed ahead of expenses over the past three years, and we expect this trend to continue. Next year, we will again make history with ITSC 2007 in Beijing, enabling thermal spray technology to reach new markets in a global marketplace. This will be the first ITSC event organized under our new partnership agreement with the DVS. The Thermal Spray Handbook has been very successful with more than 640 copies sold so far. What began as a revision of the written lessons of the Thermal Spray Home Study course grew into something much more than that, including updated photographs and new areas such as cold spray. My students are always borrowing my own copy, and I have to make sure that it comes back each time! Another outcome of the TSS Training Committee’s efforts is our Practical Learning Series modules – something we can market more aggressively, especially the module on safety. I’m particularly proud of the way our TSS Safety Committee has made thermal spray safety information available to the overall community. As a professional society, TSS has a responsibility to be proactive in making this kind of information available to everyone. I would encourage the industry leaders of the thermal spray community to step up and sponsor the distribution of this important safety information. With the ITSC event taking place here in North America every three years, we’ve also found opportunities for programming activities that are more focused and regional. These have included the Cold Spray meeting and the Sensors & Controls meeting, both in 2004, and the Combustion Turbines Coatings regional meeting in 2005. We are looking to repeat these successes, add to them, and create a standardized model. The TSS Accepted Practices Committee on Metallography has also made good progress. They are looking at a series of commonly-used coating materials, using enough samples that they can do a “round-robin” series of evaluations, polished by different labs, then analyzed and compared on a statistical basis. The committee is then publishing the results as an Accepted Practice. I would also like to cite the continued success of the Thermal Spray Discussion President’s Note: Listserv. We are always vigilant to prevent overly commercial messages from This second issue of iTSSe appearing on the listserv, but TSS is generally pleased with the quality of the sees Chris Berndt, TSS material and the willingness of TSS members to offer help and advice. Past President and former editor of the Journal of TSS has developed a new newsletter, International Thermal Spray and Surface Thermal Spray Technology Engineering or iTSSe, launched during ITSC 2006 in Seattle. Initially iTSSe will be (JTST), taking over the role bundled with ASM’s Advanced Materials & Processes magazine, so it will reach of technical editor from a sizable reader market and help us to achieve our goals of promoting TSS, TSS President Rick Knight. From the outadvancing thermal spray technology, and serving the interests of our members. set TSS wished for a long-term editor; however, initially it was more important to So where does TSS see itself in the future? We are very excited about the publish the inaugural issue in time for ITSC “proof of concept” of the Integrated Enterprise web platform for TSS members. 2006. With that accomplished, the TSS This will benefit our members, becoming your individualized portal to the world of leadership was able to focus on identifying thermal spray. someone with the right experience and The success of TSS is a team effort. It’s all the people and the chairs and the technical background to take over, and who better than Chris Berndt? Chris brings participants, all the people who support us at ASM, all of our members, who his many years of editorial experience with enable things to happen. As TSS President, it has been a pleasure and an honor JTST to the table, and through his continto work with everyone to achieve progress for our membership and for the entire ued involvement with JTST as chair of the thermal spray community. Editorial Committee, will be able to mini-

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mize overlap between the two ASM-TSS publications, thus benefiting both iTSSe and JTST. Currently located at James Cook University in Australia, Chris is well positioned technically and geographically to ensure that iTSSe is truly international in its coverage. – Rick Knight

Richard Knight, FASM 2004-06 President, ASM Thermal Spray Society Based on the President’s Address at the ASM Thermal Spray Society membership meeting at ITSC 2006 in Seattle

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In industries that use heavy-duty parts for mixing, grinding, or other techniques that subject the tools to significant wear and tear, anti-abrasion protection is imperative. Technogenia, a manufacturer of hardfacing products, has developed a special tungsten-carbide powder known as Spherotene that, when deposited on the tool’s surface, provides exceptional anti-abrasion solutions. The carbide particles are applicable by a welded-on cast-nickel cord, thermal spray, special castings, or precision laser, providing almost 10 times a longer service life than with more traditional chrome-carbide hardfacing. The tungsten-carbide hardfacing forms a metallurgical bond with the base metal on the part to protect against wear and impact. The Spherotene powders consist of spherical particles of monocrystalline tungsten carbide that are extremely hard, between 1800 and 4000 HV (Vickers Hardness). The applicable cords, TECHNOSPHERE and TECHNODUR, are reels of flexible, nickel-core wire coated with Spherotene. These two types differ in carbide hardness and are available in diameters ranging from .1 to .5 in. to be welded to parts with an oxy torch for achieving the desired degree of anti-abrasion and impact protection. The powders can also be applied as a thermal spray, using an oxy torch. The Technokit 2000 is available for this hardfacing method, which is useful for thin application, glassworks industries, or even to serve as a rust-inhibiting undercoat. For more information: TECHNOGENIA, Guy Maybon, 325 Westinghouse Blvd., Charlotte, NC Fig. 1 – Bucket wheel teeth after appli28273-6223; tel: 704/587-7107; [email protected]; www.technogenia.fr. cation of tungsten-carbide hardfacing cord by welding

INDUSTRY NEWS

Hardfacing products keep industrial parts strong

TiN coating offers increased durability, abrasion resistance

Fig. 2 – Welding a tungsten-carbide hardfacing cord to a fan blade

Powder coating educational seminar offered to colleges The Powder Coating Institute (PCI) has developed a one-hour multimedia presentation for college students on the powder coating process, which is available to travel to the classroom at no charge. The presentation covers the process, related equipment, and features and uses of powder coating, and consists of a brief video, display samples of powders and powder coated parts, and live instruction by a powder coating industry expert with a Powerpoint demonstration, along with a follow-up Q&A session. Students will receive full-color handouts illustrating the basics and benefits of powder coating technology, and the professor will receive a complimentary copy of Powder Coating – The Complete Finisher’s Handbook, the 500-page powder coating textbook published by PCI. For more information: Jeff Palmer, PCI Communications Director, The Powder Coating Institute, 2121 Eisenhower Avenue, Suite 401, Alexandria, VA 22314; 703/684-1770; jpalmer@powdercoating. org; www.powdercoating.org.

Victrex launches two series of coatings

A new line of Holtest bore gages from Mitutoyo America Corporation employs a titanium nitride coating to offer increased durability and abrasion resistance while making high accuracy, three-point bore diameter measurements. The measuring pin contact faces of the Mitutoyo Holtest and Digimatic Holtest models of bore gages are coated with titanium nitride. As a result, the pins can be made of hardened steel instead of more brittle carbide, providing extra toughness to reduce the likelihood of contact faces being chipped during measurement. The three-point design of the Holtest bore gages assures smooth, highly stable measurement in the ranges above 8mm bore diameter while a constant-force ratchet minimizes measurement variations between different operators. Optional extension rods can be fitted to enable measurement of deeper holes. For more information: Mitutoyo America Corporation, 965 Corporate Boulevard, Aurora, IL 60504; tel: 630/978-5385; [email protected]; www.mitutoyo.com.

A new product line, VICOTE Coatings, has the potential to extend the life of automotive, industrial, consumer cookware, and food processing applications by between 50% and 200% when compared with traditional fluoropolymer coatings due to excellent scratch, wear, heat, and chemical resistance, says Victrex. The key ingredient of VICOTE Coatings is VICTREX PEEK polymer, a linear, aromatic, semi-crystalline polymer. VICOTE Coatings offer excellent adhesion to the substrate, negating the need for a primer during the coating process. This and the ability to achieve very thin coatings contribute to reductions in systems costs. VICOTE Coatings 700 Series is a range of powders for electrostatic coating depending on the coating thickness required. VICOTE Coatings 800 SERIES are completely new dispersions where thinner coatings are required or where difficult geometries must be coated and which have been formulated to enhance the properties of the pure VICOTE products. For more information: Dave Wiggins, Victrex USA Inc., 3A Caledon Court, Greenville, SC 29615, tel: 215/412-8287; [email protected]; www.victrex.com. iTSSe

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INDUSTRY NEWS

Metallisation system protects future of hotel

Anti Corrosion Protective Systems (APS), based in Dubai, chose the Metallisation Arcspray equipment as the preferred system to protect the Burj Al Arab hotel, after being awarded the contract from the Jumeirah Group to spray the vital structural components of the hotel frame to protect against corrosion. In total 10,000m2 of steelwork was arc sprayed over an intermittent six-month period. The surface was first grit blasted to SA 2.4 cleanliness and then sprayed with 150Pm of aluminum using Metallisation’s Arcspray 140 and Arcspray 700 systems. An epoxy sealer and three coat paint system was then applied for aesthetic reasons and finished with a topcoat of 50 microns of polyurethane. The aluminum coating should guarantee a 15-20 year protection against corrosion in the harsh, coastal environment. In the Arcspray process the raw material, in the form of a pair of metallic wires, is melted by an electric arc. This molten material is atomized by a cone of compressed air and propelled toward the work piece. The molten spray solidifies on the component surface to form a dense, strongly adherent coating. Metallisation’s newest system, the Arcspray 170, offers high throughput with large diameter wires (1/8” and 3/16”) and is the recommended system for large scale, anti-corrosion applications. The Arc 170’s patented Synchrodrive push/pull system has no motor in the pistol, resulting in a lighter hand-held spray gun, which has a 10m wire dispense distance. The 700Amp energizer is designed with a harsh environment in mind, with all control electronics sealed from dust intrusion. For more information: Stuart Milton, Metallisation, Pear Tree Lane, Dudley, West Midlands, DY2 0XH, England; tel: +44 1384 252 464; [email protected]; www.metallisation.com.

Thermally sprayed golf clubs achieve improved backspin SpinPro, a technologically advanced hard and wear resistant coating applied to the clubface of short irons and wedges to improve backspin up to 2.5 times, delivers high spin rate through a unique texture, definitive surface roughness, and an optimized microstructure and modulus of elasticity. LinSpray technology was developed by Linde AG, Linde Gas Division, then put into practice at Linde’s Application Technology Centre. The faces of different clubs were coated and the process optimized to obtain the best possible result by using a special spraying material and the required industrial gases as carriers of thermal and kinetic energy. Sulzer Metco is the exclusive licensee of SpinPro golf club coatings. For more information: Peter Heinrich, Linde AG, Linde Gas Division, Carl-von-Linde-Strasse 25, 85716 Unterschleissheim, Germany; tel: 0049 89 31001 564; [email protected]; www.spinpro.de.

BRIEFS The first Arcelor Prize for Innovation was awarded to the “ARCEO” project. A partnership between Arcelor and the Region of Wallonia, the project aims to develop a prototype production line for a plasma vacuum process that coats steel with innovative coatings, which introduce new functions such as decorative finishes, with new metallic color and textures, self-cleaning and bacteria-resistant surfaces, “smart” surfaces (light emission or absorption), and protection including anti-corrosion features. www.arcelor.com. Wall Colmonoy Corporation has released a new data sheet on Nicrobraz 31 brazing filler metal that includes data on burst strength, composition, brazing range, oxidation resistance, and application methods. Data sheet No. 2.1.7.1 may be downloaded from the Wall Colmonoy website. www.wallcolmonoy. com Bruno Allmendinger, CFO of Sulzer since 1998, wishes to take early retirement in 2007. Peter Meier has been selected as his successor. Meier, who joined the corporation in 1992, is currently head of Finance and Controlling at the Sulzer Metco division. He will assume his new function on March 1, 2007. www.sulzer.com Michelman, a leading global manufacturer of performance enhancing coatings headquartered in Cincinnati, Ohio, announces the acquisition of Fischer Pro, Inc. of Keokuk, Iowa. Fischer Pro is a leading manufacturer of non-skid coating products for corrugated cartons, tier sheets and multi-wall bags. The acquisition includes the manufacturing operation located in Keokuk, all intellectual property, and sales. www.michem.com Hardcoat Anodizing, the latest in a series of informational fact sheets on anodizing, has been released by the Aluminum Anodizers Council (AAC). The one-page full-color fact sheet combines process data and photographs representing features, benefits, and applications of hardcoat anodizing. www.anodizing.org Southwest United Industries, Tulsa, OK has closed the purchase of all outstanding shares of CEEL Limited, Brampton, Ontario. CEEL provides hard chrome and sulfamate nickel plating services to aerospace, military, and general industrial customers. Southwest’s top priority is to support the Canadian aerospace community with the installation of HVOF thermal spray coating and grinding into the CEEL facility with Ti-Cad plating and additional processes to follow. www.swunited. com Integran Technologies Inc., Toronto, Ontario, has licensed its nano Cobalt plating process to Enduro Industries Inc., Hannibal, Mo., for deployment as an alternative to hard chrome plating in the fluid power market. A subsidiary of PTC Alliance, Enduro is a major manufacturer of hard chrome steel bars and tubes for the fluid power industry. Integran has granted Enduro a license with limited exclusivity for the fluid power steel bar and tube outside diameter coating market. www.integran.com Morris Warino has been appointed Business Development Manager for Wall Colmonoy Corporation (WCC), Oklahoma City, which is part of the WCC Aeronautical and Aerospace Group. www.wallcolmonoy.com

The effect of a SPINPRO coated club

Williams Advanced Materials Inc. (WAM) announced a major expansion of thin film chamber services at its Buffalo, N.Y., facility. Chamber services is an expanding part of WAM’s total service element for its physical vapor deposition base. The additional capacity will support the growing needs of WAM’s Eastern U.S. customers within the semiconductor, microelectronics, and data storage markets. www.williams-adv.com

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Lysa Russo Stony Brook University Stony Brook, New York For the past eight years, the NSF-MRSEC Center for Thermal Spray Research at Stony Brook has been at the heart of a number of exciting and fundamental initiatives to enhance the scientific base of thermal spray coating technology. The Center welcomes industrial participation, from sharing in research results to funded programs in specific study areas. The goal is to create a mutually beneficial arrangement; students and faculty develop an industrially-relevant perspective and companies learn about cutting-edge fundamental research. Central to our outreach efforts is the Consortium on Thermal Spray Technology, initiated in April 2002. Currently the Consortium includes 16 leading thermal spray involved companies, from powder and equipment manufacturers to endusers. All members help to formulate the annual pre-competitive research goals, which are carried out by senior CTSR staff. The Consortium was founded on the premise that thermal spray technology offered a perfect platform for precompetitive, collaborative research projects between end-users (OEMS), applicators, material and equipment develop-

INDUSTRY NEWS

SUNY Stony Brook hosts Consortium on Thermal Spray

ers, and leading research institutions. Through combined resources and expertise the group has tackled projects ranging in scope from plasma optimization and mapping of yttria stabilized zirconia ceramics to elastic/plastic properties of HVOF, APS, and VPS sprayed superalloy bond coats. Annual training workshops and classes are also used as a mechanism of keeping the group abreast of the latest advances being made not only in thermal spray but surface engineering as a whole. The coming year’s work expands the use of process maps into hard chrome replacement coatings, namely HVOF and APS applied tungsten carbide/ cobalt and nickel chrome/chrome carbide materials. The goal is to understand parameter variables and their influence on resulting coating properties as they relate to a given application. The Consortium also provides a mechanism to explore novel thermal spray applications, such as those in the electronics and silicon chip manufacturing facilities and military installations. For more information on activities or membership: Lysa Russo, Stony Brook University, Center for Thermal Spray Research, Stony Brook, NY 11794; tel: 631/632-4567; [email protected]; www.matscieng.sunysb.edu/ctsr.

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INDUSTRY NEWS

New prismatic film boosts brightness, hides moiré for LCD screens

GE Plastics’ New Illuminex ADF film is a prismatic film that provides manufacturers a superior alternative to existing materials for LCD displays. Typical prism films often have issues with moiré due to the pitch of the prism film and the pattern of the LCD pixels. Frequently, a top diffuser and/or slight rotation of a typical prism film must be used to minimize moiré. Illuminex ADF film uses a patented, proprietary pattern to reduce this moiré effect without having to rotate the film. The film features excellent optical properties that are created using proprietary GE coatings applied to a high-quality polycarbonate (PC) optical film. With Illuminex ADF film, customers have achieved improved luminance of up to five percent higher than best-in-class competitors. Illuminex ADF film can be superior in reliability to coated polyethylene terephthalate (PET) film, offering performance in high-temperature and high-humidity environments due its higher Tg (130 C) of the base film. Further, because they hide moiré and defects so effectively, Illuminex ADF films may allow manufacturers to avoid adding a top diffuser film, lowering system costs. For more information: Christopher Tessier, GE Plastics, Pittsfield, MA; tel: 413/448-6926; [email protected]; www.geplastics.com.

Rolls-Royce and Japanese Materials Institute to develop superalloys Rolls-Royce has launched a multi-year agreement with Japan’s National Institute for Materials Science (NIMS) to undertake research program into the development of hightemperature superalloys for use in gas turbine engines. The agreement brings into being the Rolls-Royce Centre of Excellence for Aerospace Materials, based at NIMS’ Sengen site in Tsukuba, north of Tokyo. It is the first scientific research program the company has directly funded in Japan. Both competitive and environmental benefits result from increasing the temperature capabilities of materials operating in the hottest parts of a gas turbine to improve fuel efficiency, which in turn reduces the emissions of carbon dioxide (CO2). Working arrangements will closely follow those of the network of Rolls-Royce University Technology Centres (UTCs) that each undertake a range of projects for Rolls-Royce in targeted technical areas and operate on a long-term ‘rolling’ horizon of five years. Rolls-Royce has worked with NIMS for around 15 years, during which time they also collaborated with existing RollsRoyce UTCs. This is expected to continue during future work programs – with Cambridge University, experienced in the physics of blade alloys, Birmingham University, which studies the castability of materials, and Cranfield University that focuses on coatings developments. For more information: Gary Atkins, Rolls-Royce plc; tel: +44 (0)1332 248389; [email protected]; www. rolls-royce.com.

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The Hybrid Spray System P.S. Mohanty, D. Kosikowski, and J. Stanisic Additive Manufacturing Process Laboratory (AMPL) Department of Mechanical Engineering University of Michigan-Dearborn Dearborn, Michigan any variants of thermal spraying technology exist. Among them, the high-velocity oxy-fuel (HVOF) spray, plasma spray, and arc spray technology have found major applications in industry. HVOF spray results in hypersonic flame gas velocities and powder particles attain high heat and high velocities. This permits particle flattening upon striking the substrate, thus forming a dense coating. Plasma spray (PS) technology has its own niche applications, especially in spraying of ceramic/refractory materials. Although very high temperatures are obtained in the plume, the particle velocities in plasma spray are lower than the HVOF process. As a result, HVOF sprayed coatings often have properties superior to those of plasma sprayed coatings. The twin-wire arcspray process, on the other hand, is a widely used method for application of low-cost metallic coatings. Coatings formed using electric arc-spray guns are relatively less dense, but deposition rates are much higher compared to the HVOF as well as the plasma process. The Additive Manufacturing Process Laboratory (AMPL) at the University of Michigan has recently embarked on an ambitious goal of exploiting the benefits of the above-mentioned processes.1,2 The so-called “hybrid process” combines electric arc and HVOF/PS spraying; molten metal at the arc is atomized and rapidly propelled to the substrate by a HVOF/PS jet. The “hybrid” concept offers many advantages. The process offers all the benefits of wire stock and productivity of arc spraying combined with the capabilities of HVOF/PS processes. Besides producing high throughput dense coatings, the gun can also tailor the composition of the coating by introducing reinforcement particles (e.g. carbide) into the HVOF/PS jet, to cater to specific property requirements such as a functionally graded material (FGM). Due to its flexible design (Fig. 1), the hybrid gun can operate in many distinct modes. For example, in HVOF/arc coupling, the gun can operate in partial-hybrid mode (I), where the material is introduced via arcing of wires only. The robustness of the hybrid gun allows it to be operated in two-wire arc or four-wire arc mode. In fullhybrid mode (II), the material is introduced through both arcing of wires and as a powder or wire through the HVOF feed line. In HVOF mode (III), the material is fed as either a powder or a single wire to the HVOF gun. In this Fig. 1 – Schematic view of the HVOF/Arc hybrid gun. mode the hybrid gun is essentially a typical HVOF gun. In arc mode (IV), the propylene and oxygen gases are replaced with air or nitrogen leading to a typical arc gun. The multitude of interdependent process parameters results in a range of particle characteristics within the spray plume. Some observations of the DPV-2000 system are summarized here. In mode

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I, the magnitude of the average particle velocity is much higher (~300 m/s) than a conventional wire arc gun (~130 m/s).3 The corresponding particle temperature and mean diameter do not vary greatly through the slices of the plume. A high speed camera image of the at- Fig. 2 – High speed camera picomization behavior in mode I is shown ture during mode l operation. in Fig. 2. In Mode III, particle velocities up to 400 m/s were observed. This is lower compared to the commercial HVOF guns (~500 m/s).4 The current HVOF component is designed to operate at low combustion rates and is air-cooled, whereas the commercial HVOF guns operate at high combustion rates and use water cooling. In full-hybrid mode (II), the particles had intermediate velocities. The efficacy of the “hybrid” system in fabricating FGMs is demonstrated in Fig. 3. This net-shape FGM is made from B4C-Al materials system. The thickness of this sample was approximately an inch. The smooth compositional variation across this thickness is evident from Fig. 3b. The detailed microstructures from various regions of this sample are shown in Fig. 3c. The quality of the deposit is self evident from these microstructures. The coating integrity was excellent and lacks any significant porosity, which indicates the possibility of use as structural components. Although the deposit Fig. 3 – B4C and Al FGM. (a) 1” thick thickness was large compared to disc. (b) macrostructure showing conwhat is normally practiced in tinuous variation of B4C. (c) microstructhermal sprayed deposits, no ap- ture at different locations. parent crack and distortion was visible in these samples. This B4CAl FGM is designed to cater to applications involving very high hardness at one end with graded ductility through the matrix to iTSSe absorb kinetic energy. References 1. D. Kosikowski, M. Batalov, and P. S. Mohanty, Functionally Graded Coatings by HVOF-Arc Hybrid Spray Gun, Proc. Int. Thermal Spray ConfITSC05, 2005, p 444-449. 2. D. Kosikowski, M. Batalov, and P. Mohanty, In-Flight Particle Characterization of HVOF-Arc Hybrid Gun, Proc. Int. Thermal Spray Conf-ITSC05, 2005, p 785-790. 3. P. S. Mohanty, R. Allor, P. Lechowicz, R. Parker, and J. Craig, Proc. Int. Thermal Spray Conf., 2003, p 1183-1190. 4. M.P. Planche, H. Liao, B. Normand, and C. Coddet, Relationships Between NiCrBSi Particle Characteristics and Corresponding Coating Properties Using Different Thermal Spraying Processes, Surf. Coat. Technol, 200(7), 2005, p 2465-2473. For more information: Dr. Pravansu S. Mohanty, professor of mechanical engineering, Additive Manufacturing Process Laboratory (AMPL), Department of Mechanical Engineering, The University of Michigan - Dearborn, 4901 Evergreen Road, Dearborn, MI 48188; tel: 313/593-4254; [email protected]; http://ampl.engin.umd.umich.edu/. iTSSe

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HOW TO . . .

How to Characterize a Thermal Spray Coating Using Electron Microscopy Doug Puerta IMR Test Labs Lansing, New York Despite all of the advances in metallographic techniques over the past two decades, there are still a number of coatings that cause problems within the metallography lab. Frequently, these coatings will take on different appearances based on the preparation recipe used. From a metallography standpoint, there is no single method that can be relied upon to prove the true structure of the coating. Fortunately, there are simple alternatives to metallography that can be used to characterize a thermal spray coating. This article will discuss one such method, which involves using a scanning electron microscope (SEM) to examine a cryogenic fracture of the coating. The procedure for creating a cryogenic fracture of a coating is very similar to the procedure used for creating a fracture grain size sample of martensitic steels (per ASTM E 112). A thin section of the sample is submerged in liquid nitrogen until “frozen,” removed from the liquid nitrogen, and quickly overloaded to fracture the sample (keeping the coating in tension). Examination of a coating fracture surface often reveals features that may have been masked or exaggerated by metallographic preparation. A good example of a coating that can be characterized by this technique is tungsten carbide-cobalt (WCCo). WCCo is a coating that is frequently mis-prepared during metallographic preparation. In some cases, carbide particles are fractured and/or “pulled-out” of the coating, artificially increasing the apparent porosity. In other cases, Fig. 2 – Cross-sectional view of a nickel-aluminum bond coat. the cobalt phase may be smeared over inherent porosity, therefore decreasing the The red arrows in this image are used to identify porosity apparent porosity. As shown in Fig. 1, a cryogenic fracture surface of the coating can between the splat particles. give the operator a sense of the true porosity present within the coating. Within this fracture surface, pores are readily visible that should correspond to porosity in a mounted and polished sample. Another application for cryogenic fractures relates to the classification of interfaces between splat particles. Depending on the operator and specification, features such as those shown in Fig. 2 may be classified as either porosity or oxides. Analysis of a cryogenic fracture of this sample verifies that these features are in fact porosity. Figure 3 shows a low-magnification view of a nickel-aluminum coating, from which the general structure of the coating can be seen. Figure 4 shows a higher magnification view of what appears to be an individual splat particle. In this case, the smooth appearance suggests a lack of particle bonding. Figure 5 shows another region of the coating at higher magnification, where porosity is again present between particles. The presence of linear porosity, as compared Fig. 3 – SEM micrograph of a cryogenic fracture surface of to stringer oxides, can also be verified using a low-viscosity cold mount epoxy a nickel-aluminum coating. The area within the red box is containing a colored dye. This procedure was discussed previously in iTSSe (Vol. shown in greater detail in Fig. 4. iTSSe 1, Issue 1). Fig. 1 – Cryogenic fracture surface of a plasma sprayed WCCo coating. The fracture surface contains a number of pores and cavities (red arrows), which represent porosity within the coating. Photo courtesy of Pratt & Whitney Quality and Standard Laboratory.

Reference A.R. Geary, Metallographic Evaluation of Thermal Spray Coatings, Technical Meeting of the 24th Annual Convention, International Metallographic Society, July 1991, Monterey, CA, p 637.

Fig. 4 – SEM micrograph showing one surface of a splat particle. The smooth appearance of this surface suggests that this particle was not originally bonded to its neighboring particle.

Fig. 5 – SEM micrograph showing another region of the nickelaluminum coating. Porosity (red arrows) can be seen between the splat particles.

For more information: Doug Puerta, IMR Test Labs, 131 Woodsedge Drive, Lansing, NY 14882; tel: 607/533-7000; dpuerta@ imrtest.com; www.imrtest.com.

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FOCUS ON

Monitor Coatings Monitor Coatings Limited has, in one form or another, been in operation since 1927, predominantly as an engineering company, introducing thermal spraying to its portfolio in the late 1970s. The initial focus was on high end technology aerospace applications, but the business was further developed to encompass the steel manufacturing and directional drilling industries. In addition to thermal spraying, Monitor has also developed slurry coating technology (with two international patents), which can be used either independently or in combination with thermal spraying enhancing component performance. Monitor’s historical focus on aerospace applications led to troubled times following the events of 9/11/2001. A subsequent management buy out by the now private owners, Bryan Allcock, managing director, and Malcolm Findlay, operations director, allowed for significant investment and relocation to the purpose built facilities and significant expansion into overseas markets. Monitor’s UK facilities currently employ 38 people with recruitment being a top agenda item in order to meet the company’s rapid but sustainable growth. Monitor Coatings Limited has virtually zero staff turnover with several employees already having completed more than 40 years service. One of the most significant achievements for Monitor has been recognition through winning the Manufacturing Business Awards and North Tyneside Small Business Awards 2004. Monitor offers a full range of thermal spray and related services including wire, arc, plasma, HVOF and one of the largest low pressure plasma units in the market. In close partnership with its local supply chain, Monitor offers weld repair, machining, and specialist grinding for pre- and post-coated components. Monitor’s unique range of slurry coatings offer the ideal partner to thermal spray, enabling state of the art ceramic sealing capabilities and stand-alone non-line-of-sight alternative technology. Monitor Coatings continues its 30-year tradition of servicing the aerospace and gas turbine industry sectors. Monitor now boasts Merit status on its well-established NADCAP accreditation together with AS9100, ISO 9000-2000, and numerous other customer approvals. Other core markets include the steel manufacturing industry, oil and gas based directional drilling, and newer markets, including steam turbines and biomass incinerators. While developing the business into new sectors, Monitor also maintains its roots, continuing to provide a quality service to traditional markets providing solutions to wear and corrosion resistance on rotating and reciprocating parts. In conjunction with its foreign partners Monitor looks forward to further developing an exciting range of processes including micro-laser welding for in-situ repair of hard face coatings, fusion welding, and narrow bore internal coatings. The last three years have been focused on the globalization of the company. Monitor now has established joint ventures in Singapore as Fusion Monitor and Abu Dhabi as Rainbow Monitor. Monitor Coatings also has secured partnerships in the USA based around core technology transfer. As part of its commitment to global customer service, Monitor has just launched a full range of slurry coatings to be made available to applicators around the world. The range includes sealing technology for HVOF hard-face coatings, high temperature (2000

THE SPRAY SHOP

Monitor Coatings factory

ºC) and ultra high wear resistance slurry coatings for a diverse range of “hard to reach” applications. Recently added variants include diffusion coatings for high temperature oxidation resistant applications. Monitor credits its success to a unique style of management, a commitment to sustained investment, and a continual Winners of the North Tyneside Small search for new innovative Business Awards 2004 (from left): Dr. Bryan solutions to protection in Allcock, managing director; Cllr. Linda Arkley, mayor of North Tyneside; and Mr. Malcolm extreme environments. Findlay, operations director. Over 12% of Monitor Coatings’ turnover is re-invested in research and development projects including national and international collaborative iTSSe research. Contact information: Dr. Bryan Allcock, Managing Director, Monitor Coatings Limited, 2 Elm Road, West Chirton North Industrial Estate, North Shields, Tyne & Wear NE29 8SE, United Kingdom, tel: +44 191 293 7040; fax: +44 191 293 7041; [email protected]; www.monitorcoatings.co.uk. iTSSe

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A Winning Alternative to Hard Chrome in Deep Bore Applications P. Ruggiero and Marc Froning Engelhard Corporation East Windsor, Connecticut

Overview The aerospace industry has been aggressively seeking alternative methods to hard chrome plating, especially for deepbore parts that can be difficult to coat. This has taken on an even greater urgency now that the Occupational Safety and Health Administration (OSHA) has announced a new, sharply lower permissible exposure limit (PEL) for occupational exposure to hexavalent chromium (HC). Effective May 30, 2006 the PEL for HC workers is reduced from 52 micrograms to 5 micrograms in an 8-hour time weighted average (TWA). OSHA said it was undertaking the action to reduce the “significant health risks” posed by HC. This mandatory reduction in PEL will undoubtedly continue to expand the need for alternative coating solutions. Even before the recent announcement of stricter PELs for hard chrome coating applications, manufacturers and processors had been embracing alternative coating systems. One of the most promising alternatives is high velocity oxygen fuel (HVOF) spraying with a material of tungsten carbide cobalt chromium (WC/CoCr). Historically this alternative was technically restricted to components coated on external areas or components with internal areas no greater in length then the size of the inside diameter (ID) to be coated, but new off-angle spray techniques are making the process more widely applicable. Traditional HVOF techniques can be used to coat up to 75 to 80 percent of aerospace components. Today, new off-angle, line-of-sight HVOF techniques can be used to coat increasingly deep-bore parts. A deep bore coating length of 3X the entrance diameter can now be achieved. Background The aerospace industry has long used electrolytic hard chrome (EHC) coatings to protect components from wear, abrasion, and corrosion, and to restore dimensions of worn parts. Compliance with increasingly stringent environmental and safety regulations and the need to improve coating performance to reduce life-cycle costs, has driven increased interest in thermal spray technology for aerospace applications.1 HVOF has become one of the more valued alternative techniques. As a line-of-sight process, however, HVOF had application limitations, particularly in coating small internal diameters, such as landing gear inner cylinders/sleeves and hydraulic actuator housings. Many processors would not consider HVOF spraying techniques because the angle of the spray was problematic. Specifically, the line-of-sight process was restricted in its ability to coat inside diameters any greater then the size

Traditional ID plasma spray application Coated from the outside

HVOF ID spray application Coated from the outside

30 deg

45 deg

Height = width of cylinder

Fig. 1 – Off angle applications

of the ID. Essentially, a 45 degree angle was the maximum angle possible. However, recent studies have shown that new techniques can overcome these limitations. Study parameters In one study,2 HVOF WC/CoCr coatings were sprayed at several angles while maintaining consistent combustion characteristics and standoff distance. Parts only having a two-inch ID were effectively coated up to six inches in depth. With the exception of the wear and fatigue samples, the coatings were sprayed onto grit-blasted AMS 5504 stainless steel. The substrate alloy for the wear and fatigue testing was AISI 4340 steel. The as-sprayed coating thickness for all samples was 250300 Pm (0.010-0.012 in.). The final coating thickness of the fatigue samples after grinding was 76 Pm (0.003 in.). The spray angles examined in this study were 90, 60, 45, 35, and 25 degrees, with respect to the substrate surface (Fig. 1). Average surface roughness (Ra) and bearing length ratio (Tp%) were measured for each as-sprayed coating. The coatings were sectioned and mounted in cross-section in epoxy for micro hardness testing and microstructure evaluation. Additionally, the surfaces of the coatings were polished and the microstructure of the bearing surface was examined using scanning electron microscopy. Tensile bond strength testing was performed per ASTM C633. Relative measurements of residual stress in each coating were determined using the Almen strip deflection method. Fretting wear testing was performed to determine the relative wear resistance of HVOF WC/CoCr coatings sprayed at 25, 35, 45, and 90 degrees. The HVOF WC/CoCr coatings were applied to the moving sample. The static sample was composed of either NiAl-bronze or AISI 4340 steel. The wear tests were conducted under room temperature, non-lubricated conditions in air. The applied load was 1.8 MPa (265 psi) and the frequency was 300 Hz.

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Summary and conclusions Standard measured responses for coatings, such as micro hardness and Almen deflection, indicate that the extreme offangle HVOF WC/CoCr coatings are different from the 90° coatings in several significant ways. Off-angle coatings exhibit lower hardness and lower compressive residual stress. As a benefit, off-angle coatings also exhibit more uniform distribution of phases across the surface and lower as-sprayed roughness. Despite the reduced hardness and residual coating stress, the off-angle WC/CoCr coatings exhibited less wear, as measured by change in thickness, than the 90 degree coatings. These observations indicate that the distribution of phases, not micro hardness, in the composite coatings is more important in predicting wear response. The improved phase distribution in off-angle WC/CoCr coatings appears to be caused by blending that occurs on impact as the splats elongate, flatten, and splatter. Under dry fretting wear conditions against HVOF WC/CoCr coatings, both NiAl-bronze and 4340 steel wear by adhesion to the coating; however, the adhesive wear is more significant in the case of the bronze. The higher ductility of the bronze sample likely allowed greater plastic deformation under the normal and shear forces in the wear test. In addition to material loss through adhesion to the WC/CoCr coating, the bronze sample also exhibited characteristics of surface fatigue wear. The wear scar on the steel surface did exhibit plastic deformation and embedded WC wear debris, but no evidence of surface fatigue. These study results have been confirmed with successful experience in the field. For example, Engelhard coats parts for the F-18 Hornet and the Joint Strike Fighter aircraft utilizing similar angles of spray. To meet OSHA’s stricter permissible exposure level (PEL) standard for HC workers, the aerospace industry can confidently rely upon high velocity oxy-fuel (HVOF) spraying with tugsten carbide cobalt chromium (WC/CoCr). New offangle spray techniques are extending applications into entrance bores, and offering enhanced coating options to the vast majority of aerospace components in the iTSSe aerospace marketplace.

Surface Finishers Society, Inc., 2000, p 131-139. 2. E. Strock, P. Ruggiero, and D. Reynolds, The Effect of Off-Angle Spraying on the Structure and Properties of HVOF WC/CoCr Coatings, Thermal Spray 2001: New Surfaces for a New Millennium, C.C. Berndt, K.A. Khor, and E.F. Lugscheider, Ed., May 28-30, 2001 (Singapore), ASM International, 2001, p 671-676

For more information: Peter Ruggiero is sales and marketing manager at Engelhard Corporation, 12 Thompson Road, East Windsor, CT 06088; tel: 860/623-9901; [email protected]; www.engelhard.com/hvof.

References 1. B.D. Sartwell, K. Legg, and P. Bretz, Status of HCAT/JG-PP Program on Replacement of Hard Chrome Plating with HVOF Thermal Spray Coatings on Landing Gear, Proceedings of AESF Aerospace Plating and Metal Finishing Forum, American Electroplaters and iTSSe

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OSHA Hexavalent Chromium Regulation

here is a buzz among thermal date for the law was 90 days from that date, which was May 30. On May 30, the clock sprayers and other industries about started ticking toward the November 27, 2006 the newly adopted regulation condeadline for compliance, i.e., 180 days after cerning workplace exposure to hexavalent the effective date. May 31, 2010 is the deadchromium or hex chrome, chrome 6, Cr+6, line for installing engineering controls (4 yrs). and other commonly used terms. OSHA has “Except as permitted in paragraph (f)(1)(ii) proposed, adopted, and instituted new limits and paragraph (f)(1)(iii) of this section, the on exposure, which effectively reduced the employer shall use engineering and work permissible exposure by a factor of ten. practice controls to reduce and maintain Daryl Crawmer Hexavalent chromium is a known caremployee exposure to chromium (VI) to or cinogen that can attack the respiratory sysThermal Spray Technologies below the PEL…” Where engineering and tem and in some forms attack the skin; when Incorporated administrative controls are not demonstrably ingested, large doses are also a health conFall River, Wisconsin feasible then respirator, clothing, and hygiene cern. The primary concern for thermal controls become necessary. sprayers is airborne particulate and fumes. Studies show that Cr+6 can be produced by plasma-arc, flame (including HVOF), and electric-arc spray processes. Almost any Exposure determination and medical surveillance Following the May 30 date, an “exposure determination” chromium-bearing material can produce the hexavalent state when exposed to the high energy levels associated with thermal had/has to be made to assess each employee’s exposure to hexaspray process. Chromium oxide, MCrAlY’s, nickel-chrome, and valent chromium. If the 8-hour TWA (time weighted average) exceeds the action level, all employees exposed above the action other common materials produce hex chrome when sprayed. level must undergo “medical surveillance.” Medical surveillance involves a “medical and work history” and an examination by a Background On February 28, 2006, OSHA regulation CFR 29 1910.1026 physician. Employees must also be examined by a physician became law. This new regulation has been in the works since within 30 days after a physician’s recommendation for additional 1992 when the Oil, Chemical, and Atomic Workers International testing, after an accidental release of Cr+6, or whenever the Union and Public Citizen’s Health Research Group first peti- employee shows any signs or symptoms associated with exposure tioned OSHA to implement an emergency temporary standard to to Cr+6. HAZCOM (hazardous communication) is also triggered reduce worker exposure to 0.5? mg/m3. At that time, the OSHA at the action level. PEL (permissible exposure limit) for airborne hexavalent chromiExposure above the PEL um was is 52 mg/m3. Above the 5 mg/m3 PEL, considerable activity occurs. Leaving out the politics of what followed and getting straight to the point, in 2004 a proposed new standard for workplace Respirators and controlled clothing are required for those individexposure the chrome 6 was put forward for public comment. The uals who are exposed above the PEL. Clothing cannot be taken proposal was to lower the PEL to 1 mg/m3 from the existing 52 home from the workplace, which requires either disposable or mg/m3. That proposal was to have entered into the federal regis- washable clothing that remains at the workplace. Areas where the exposure exceeds the PEL are to be “demarter on January 18, 2006. Adoption of the regulation was delayed until February 28, 2006 and went into effect, on that date, with- cated from the rest of the workplace in a manner that adequately out fanfare or the anticipated legal backlash from either side of establishes and alerts employees of the boundaries of the regulated area.” Access to these areas must be limited. the argument.

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Action level and permissible exposure limit When it was finally adopted, the limit was set at 5 mg/m3. Another important number is the “action level” of 2.5 mg/m3. Action levels in OSHA regulations trigger activities, which will be covered further down the page. Understand, this regulation was written around and appears to have been targeted toward electroplating, chromate spraying, welding, and general construction. There is no specific mention of thermal spray. However, the first line of the regulation states: “This standard applies to occupational exposures to chromium (VI) in all forms and compounds in general industry, …” §1910.1026(a)(1) and “Chromium (VI) [hexavalent chromium or Cr(VI)] means chromium with a valence of positive six, in any form and in any compound.” §1910.1026(b). Key dates Here are the key dates and discussion on how the new regulation affects thermal sprayers. On February 28, 2006, 29 CFR 1910.1026 was entered into the Federal Register. The effective

Continued air monitoring When exposure is above the action level, but below the PEL, air monitoring must be conducted every six months until the exposure drops below 2.5 mg/m3. If exposure is above the 5 mg/m3 PEL, air monitoring must be conducted every three months. Housekeeping and hygiene Housekeeping and personal hygiene are also parts of this new regulation. Within the demarcated areas, “prohibited activities” include eating, drinking, smoking, chewing tobacco or gum, and the use of cosmetics. Housekeeping generally includes vacuuming, in lieu of sweeping, shoveling, and blowing down areas with air. There are also requirements for labeling and disposal of materials that are contaminated. Parting comments There are at least two peculiar requirements in this regulation. Continued on page 25

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Successful Consultant/Client Relationships R.C. Tucker, Jr. The Tucker Group, LLC Wesley Chapel, Florida ngineering and scientific consulting seems to be a growing field for a number of reasons (or at least the number of people working as consultants seems to be growing). Many companies are reducing their engineering and scientific staffs and outsourcing these functions to either suppliers or consultants. Some, of course, are moving these functions to lower cost countries, but in these situations they still need knowledgeable people locally to facilitate communication and implement results. Another reason for the increase in the number of consultants is that some engineers and scientists are essentially forced into consulting because they have lost their positions due to corporate changes and have not found other comparable employment. Finally, there are “senior” individuals like the author who just want to keep a hand in the technologies they have helped develop over the years. In any event it might be worthwhile to consider a few points that would help to make the relationship between the consultant and the client more effective, efficient, and beneficial to both parties.

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INTEGRITY is an attribute we all believe we have, but may be more difficult to maintain than is readily apparent. It is particularly important when it comes to protecting the intellectual property of clients. Most consultants have a number of clients, many of whom are in the same or similar fields of endeavor. Thus the consultant must always be cognizant of each individual client’s intellectual property and not convey any of it to others unless and until it becomes public knowledge. There are several forms or categories of intellectual property including patents, trade secrets, and business confidential information. The information in patents becomes public knowledge as soon as the patent is published, but a consultant may have knowledge of other related information of the client that remains confidential. Third party patented materials or processes recommended to a client by a consultant must be accompanied by a strong recommendation/warning that the client must obtain a license for use. Trade secrets and business information are often gray areas. The consultant should insist that the client clearly delineate these areas. Although such information may be, in reality, common knowledge in the field, the client’s use of it may still be confidential. Most consulting contracts and nondisclosure agreements stipulate the period of time a client’s intellectual property must be held confidential, usually three to five years. While a consultant is legally free to disclose the information after that period has expired, it is the author’s practice not to do so until after the client has published the information in a paper, presentation, or patent even though nondisclosure agreements without a time limit are undesirable. Other aspects of a consultant’s ethics that are obvious and do not need amplification include the following.

• Do not mislead the client on the extent or certainty of the consultant’s knowledge of the subject matter at hand. • Maintain accurate billing records and don’t bill to develop information the client assumes you already have. This does not exclude billing for the development of information if that is part of the contract. • A consultant normally can not assume responsibility for the safety issues involved in a project, but certainly should apprise the client of any safety concerns and try to insure that the client effectively deals with them. • A consultant should not imply in any way that he or she is a professional engineer unless, in fact, he or she is. So far the discussion has been based on the ethical requirements of the consultant, but the ethics of the client are also important. For example, it is unethical for a client to hire a consultant in an attempt to gain the intellectual property of a competitor. Although regrettable, this does on occasion happen, particularly shortly after a consultant has left the employment of the competitor. In such cases the consultant should, of course, refuse to comply with the client’s or potential client’s wishes. In addition a client should not expect a consultant to assist in violating a patent of a third party. This of course does not preclude assisting in the development of improvements or alternative processes or materials, or new applications of patented processes or materials.

COMMUNICATION between the consultant and client that is open, complete, and candid can greatly increase the efficiency and efficacy of the relationship and any projects undertaken. In spite of an nondisclosure agreement and consulting contract, some clients are reluctant to disclosure more than what they consider the bare minimum of information to a consultant. First, this does not foster a feeling of trust and confidence in the consultant, and, second, the consultant is frequently left with too little information to do an adequate and certainly not a superior job, leaving both the consultant and the client frustrated. It is probably better to error on the side of more information than is necessary than too little. The CLIENT’S OBJECTIVES are paramount in consulting. They almost always involve economics when consulting for a corporation (the opposite seemingly being true when consulting for the government). Thus issues such as process or material costs, product quality and reliability, target market size and constraints, competitive situation, et cetera must be of concern. For example, the author prefers coatings or coating systems that are of the highest quality and performance, but they may be too costly for some client’s applications, so alternative coatings or coating systems may have to be recommended that meet the client’s requirements of cost, performance, and quality, but are not “top-of-the-line”.

TIME is always of importance. A consultant should always be candid about his availability and his estimate of the time required to complete an assignment. Conversely, the client should explain their time constraints and not be unrealistic in their demands for either time of completion or consultant’s total time iTSSe

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allowed. If a consultant does not believe that he or she can meet the time requirements of the client, the consultant should not take the contract. If the consultant’s available time or total required time becomes an unforeseen problem during the execution of a project, the client should be apprised of the situation immediately.

CONTRACTS usually consist of a nondisclosure agreement and a consulting agreement, although the two may be conveniently combined. Most large corporations have their own forms that are, of course, written to protect the corporation, not the consultant. Reasonable modifications to these can and should be requested by the consultant to insure protection of the consultant. In the author’s experience, these are usually accepted. Occasionally smaller corporations do not have such preset agreement forms and will accept an agreement drafted by the consultant. Although the author is not an attorney and this should not be considered as legal advice, he believes that a combined agreement should contain at least the following elements. • Services – a general statement. A specific work scope can be attached or made a separate document. • Availability • Independent contractor – consultant is an independent contractor, not an employee of the client • Warranty – consultant warrants services will be done in a professional manner. Client warrants they will not ask the consultant to do anything illegal. • Liability – unless it is due to client’s negligence, consultant assumes liability for consultant’s injury, illness, etc.

• Confidential information – equivalent to a nondisclosure agreement when coupled with disclosable information • Disclosable information – defines public knowledge, etc. • Subject developments – consultant will assign rights to inventions made by consultant related to and during the consulting contract • Third party obligations and services – consultant reserves right to work for others in the same field so long as it does not conflict with consultants obligations to the client • Term of the agreement • Compensation • Survival – terms of confidentiality may extend beyond the end of the contract • Severability and judicial amendment – defines state governing laws and that if one part of the agreement is determined in court not to be enforceable, the rest remains enforceable. • Indemnification – client agrees to indemnify consultant against third party claims. This may be particularly important relative to the terms of consultant’s liability insurance. Undoubtedly, there are other considerations in a successful, mutually rewarding consultant/client relationship that is both efficient and effective, but hopefully the above will be of some iTSSe assistance in attaining that goal. For more information: Dr. Robert C. Tucker, Jr., President, The Tucker Group LLC, 5154 Pine Lake Road, Wesley Chapel, FL 33543-4459; tel: 813/991-9921; email: [email protected].

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Better Performance of Plasma Thermal Spray Ronald J. Molz and Richard J. McCullough Sulzer Metco Westbury, New York

Torsten Wintergerste Sulzer Innotec Winterthur, Switzerland n the thermal-spray coating process, the coating material is melted in a heat source. The molten material is then propelled by process gases and sprayed onto the base material. The particles impact on the base material, also known as the substrate, solidify, and form a solid layer. This process includes complex multiphase flow with disperse particles, heat transfer, and conversion of thermal to kinetic energy. In plasma guns used for thermal spray, the temperature in the plume can reach 16,000 K, which makes measurements of the gas flow field extremely challenging. Computational fluid dynamics (CFD) permit the examination of plasma-gun behavior in operating regimes never before explored. The use of plasma guns—plasma is an ionized gas—for thermal-spray coatings is several decades old, and these guns have since matured into efficient coating tools. In plasma guns, an arc is established between an anode and a cathode (Fig. 1). The gas flowing between the electrodes is ionized such that a plasma plume develops. The spray material is injected as powder outside the nozzle into the plasma plume, where it is simultaneously melted and accelerated toward the substrate surface. Keeping the plasma stable under a wide range of operating conditions, which includes various types of gasses and their interaction, has proven to be a considerable design challenge.

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Important design tool Industrial users of plasma thermal spray demand reduced costs by increasing production rate, increasing deposit efficiency, and extending hardware life. Today, CFD is at a point where it can serve as a design and development tool to dramatically improve the operation of a plasma gun. CFD also permits the examination of plasma gun behavior in untested operating regimes in order to extend their application range and develop new and better coatings (Fig. 2). Previously, the development and improvement of process gun hardware for thermal spray was done by empirical trial and error. Engineers and scientists would surmise what was happening inside the gun, propose solutions or improvements, manufacture parts, and test the changes. This process was often time consuming and costly. A month of CFD work can literally replace a year’s worth of physical prototyping and yield better results. The Sulzer Metco TriplexPro-200 plasma gun is an ideal platform for the application of CFD to improve gun performance (Fig. 3). Its 3 arcs permit a wider range of current, and the gun is robust enough to handle extreme operating conditions when tested at its limits. The design also facilitates the separation of gas flow and arc control, permitting a wide range of gas flow within the voltage limits of the support equipment. Finally, the turbu-

Fig. 1 — Gas flow in the nozzle of plasma spray guns and powder injection into the plasma plume are two areas where Sulzer Metco applies CFD to improve gun performance.

Fig. 2 — The current operating window of the TriplexPro-200 gun extends past the operating range of typical plasma guns on all fronts. Rear gun body Front gun body

Neutrode stack Neutrode and interchangeable insulator housing nozzle

Triple powder injector

Electrodes

Nozzle nut

Fig. 3 — The design of the Sulzer Metco TriplexPro-200 features insulated neutrode segments and the ability to change nozzles easily. It has other characteristics that allow separation of arc control from gas dynamics, providing an open architecture for optimization.

lence level is significantly lower than in the turbulent gas flow typical for other plasma guns. Systematic modeling The overall dynamics of a plasma gun are complex, and modiTSSe

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Fig. 4 — The TriplexPro200 plasma gun is provided with three different plasma-forming nozzles to suit varying application requirements (left). Nozzles currently being modeled and tested produce oval-shaped plumes, as well as other custom shapes and even one for axially feeding liquid suspensions.

eling them requires a step-by-step method. First, the model of the gas dynamics was developed assuming uniform gas temperature and validated against measurements of the TriplexPro gun instrumented for registering back pressure and flow. Once it had been confirmed that the isothermal model simulated the actual pressure and flow field in the gun, a model of the electric arcs, complete with magnetic field, was added to the gas model to heat the gas. Again, the model was validated with the actual TriplexPro gun under operating conditions of flow and pressure, now also including voltage and current. Next, the injection of powder particles into the plasma plume was included in the simulation and validated with particle temperature and velocity profiles, using an Accuraspray particle diagnostic system and custom high-speed imaging equipment. To complete the model, the mass of the gun was configured with thermodynamic properties, which were validated using the energy losses in the water

cooling circuit as well as surface temperature measurements. CFD supports development The TriplexPro-200 plasma gun comes with three nozzles (Fig. 4) that encompass a wider operating range than typical plasma guns. A wide bore, high-enthalpy nozzle produces a slow and hot plasma plume, a medium bore produces a plasma plume typical of most plasma guns, and a narrow bore convergent-divergent supersonic nozzle produces a fast and cool plasma plume. The use of CFD enables customization of each type of nozzle in terms of gas flow. Incorporating a model of the arcs into the CFD model permits further improvements to produce a stable and uniform arc pattern. The stability of the arc heats the gas evenly and assures that the arcs remain predictable over a wide range of gas flows. Further, CFD modeling supports the development of more unconventional nozzles, which allow for shaping of the plasma plume to extend the range of applications.

Calculation of the Plasma Arcs in the TriplexPro Spray Gun —>

The Lorentz force f is essential when fluid mechanics and electro-magnetic forces have to be coupled. An electric field is defined by the forces between nonmoving charges, whereas a magnetic field is created by moving charges. In the plasma spray —> gun Triplex-Pro by Sulzer Metco, the fluid that is moving in an external electric field causes a current density j, which com—> prises of three electric arcs and in turn causes a magnetic field. The interaction of the magnetic field B with the current density —> —> —> causes the Lorentz force f = j × B, which is exerted on the three arcs. The current is aligned along the main axis, and the magnetic field is oriented clockwise concentrically around the current, therefore the resulting Lorentz force points inwards, according to the right-hand rule. If this effect is considered in the simulation, the three singular arcs contract and the temperature distribution in the fluid at the nozzle outlet becomes axially centered and homogeneous. The flow simulation without (left) and allowing for the Lorentz force (right) clearly shows this effect. The electric arcs end at the nozzle outlet, whereas the heated plasma plume exits the spray gun.

HIgh Current density

Magnetic field

Lorentz force

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Product improvement An example of a CFD-based improvement that quickly made it into the production gun was an improvement in the convergentdivergent HV nozzle itself. The original 5-mm nozzle was designed to produce supersonic plasma velocities. The formation of shock diamonds in the plasma plume was an indicator that this goal had been achieved. However, the edges of the plume exiting through the divergent section of the nozzle appeared fuzzy—as if the plume was out of focus. The CFD-model images clearly showed that, with ideal operating gas flows, the gas flow separated from the diverging nozzle wall approximately two-thirds of the way downstream of the nozzle throat (Fig. Fig. 5 — A close-up of the CFD-model with the 5mm nozzle clearly shows the formation of shock 5), creating a turbudiamonds as they appear in the actual gun as well lent region between as the flow separation from the wall of the divergent the main gas flow section of the nozzle. and nozzle wall. This flow separation indicated that the nozzle was overexpanded. Once the problem had been identified, the nozzle design was changed to shorten the nozzle divergent section, a measure that reduced the Mach number, and thus eliminated the overexpansion (Fig. 6). This modification both further stabilized the plume and reduced energy loss. Further enhancement expected Sulzer Metco’s TriplexPro-200 plasma gun has already benefited from the results of CFD modeling. With this tool and the expertise of Sulzer engineers, the potential to further improve the design not only of this gun but also of conventional plasma guns is significant. As plasma guns, in general, are less than 15% efficient in applying the energy input to the coating process itself, there is considerable room for further improvement. Further CFD-based improvements will concentrate on increasing efficiency and throughput. The potential for higher operating power levels, as well as higher gas velocities and temperatures has already been demonstrated in the models using the same basic gun design. The future of plasma thermal spray iTSSe looks very bright. For more information: Ronald J. Molz, Sulzer Metco (US) Inc., 1101 Prospect Ave., Westbury, NY 11590; tel: 516/338-2580; ron.molz@ sulzer.com.

Fig. 6 — The 5-mm nozzle before and after modification as a result of the CFD gas flow model analysis. Note that the nozzle is shorter but retains the same geometry as the original nozzle. iTSSe

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Nanocomposite Materials:

An Innovative Turnover for the Wire Arc Spraying Technology P. Georgieva,* R. Thorpe, and A. Yanski Praxair TAFA Concord, New Hampshire

S. Seal University of Central Florida, Mechanical, Materials and Aerospace Engineering Department (MMAE) Advanced Materials Processing and Analysis Center (AMPAC) Nanoscience and Nanotechnology Center DURIP Plasma Nanomanufacturing Facility, UCF Technology Incubator Orlando, Florida ecently, there has been an intensive research in the area of thermal processing of nanostructured materials for their high strength and structural applications.1-9 With this intention Praxair and TAFA has introduced wire arc spray to fabricate nanostructured coatings. Research has shown that both hardness and wear resistance can easily be increased through decreasing coating grain size to nanometer range.1-9 This low cost manufacturing process could potentially solve many wear and corrosion problems. TAFA 95MXC, an iron-based amorphous type wire, has been widely used in many coating applications with success. The new Fe-based cored wires, with compositions Fe-C-B-Mo-W and Fe-CrMo-W-B, TAFA designations 100MXC and 110MXC, respectively, are known to generate distinctive, high quality nanostructured coatings. The approximate chemistries of the unique, recently devel-

R

Fig. 1 — Wire arc processing

Coatings Development The performance of the new wires was analyzed through three different wire arc systems: TAFA Models 8835, 9000, and the new advanced 9935 CoArc (Fig. 1). The spray parameters for each system were adjusted for each particular material; however, for experimental purposes the following common spray conditions were selected: 32-36 Volts DC, 175 Amps, and 60-75 psi (4.14-5.17 bar) primary atomizing gas (air) pressure. When secondary atomizing gas (ArcJet spray attachment) was used, the primary and the secondary gas pressures Table 1 – Approximate chemistries of newly developed wires were changed to 50 and 40 psi (3.45 and 2.76 bar), generating unique nanostructured coatings respectively. The ArcJet attachment enhances the arc 110MXC – V2 140MXC wire spraying process by dramatically increasing the Element, % 100MXC 110MXC New development New development particle velocity and concentration of the spray Cr < 20 < 20 < 20 < 20 stream. The high velocity and the tightly focused B