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A STUDY OF MICROSTRUCTURE AND HARDNESS ON Fe-Co/SiC COMPOSITES Noraziana Parimin, Andy Linus School of Materials Engineering, Universiti Malaysia Perlis, Kompleks Pusat Pengajian Jejawi 2, 02600 Arau, Perlis.

ABSTRACT This research was conducted to study the effect of reinforcement particles on iron-cobalt (FeCo) composites. The composition of silicon carbide (SiC) was varied from 0 to 20 wt%. The composite was fabricated via powder metallurgy (PM) method, which consists of mixing, compaction and sintering processes. The powder was mixed for 2 hours to obtain uniformity between SiC and Fe-Co matrix and compacted to a cylindrical shape at 250 MPa. Samples were sintered for 2 hours at 900oC with 10oC/minute heating rate in argon atmosphere. The influences of reinforcement particle on the sintered samples were characterized in terms of microstructure and hardness testing. The Fe-Co/20wt%SiC composites show highest hardness value.

ABSTRAK Penyelidikan ini telah dikendalikan untuk mengkaji kesan zarah-zarah peneguhan pada besi kobalt (Fe-Co) bahan komposit. Komposisi silikon karbida itu (SiC) adakah berbagai-bagai dari 0 hingga 20 wt%. Rencam telah dibuat melalui metalurgi serbuk (PM) kaedah, yang mengandungi mencampurkan, pemadatan dan proses-proses pensinteran. Serbuk dicampur untuk 2 jam memperoleh keseragaman antara SiC dan Fe-Co matriks dan dipadatkan ke satu bentuk berbentuk silinder pada 250 MPa. Contoh-contoh adalah tersinter untuk 2 jam di 900oC dengan 10oC / kadar pemanasan halus dalam suasana argon. Pengaruh-pengaruh zarah peneguhan pada tersinter contoh-contoh disifatkan dalam syarat-syarat mikrostruktur dan pengujian keliatan. Fe-Co/20wt%SiC komposit menunjukkan kekerasan tertinggi nilai. Keywords: Composite, reinforcement, powder metallurgy

INTRODUCTION Composite materials referred to the highly engineered combination of elements from different material which will offer many advantages over other materials, thus will give better properties to the development of materials. This leads to the possibility to create new composite materials with special physical and mechanical properties in a component [1]. For instance, a composite produced by compaction and sintering processes of iron-cobalt (Fe-Co) mixed powder has been used for wear and corrosion resistance materials. The development of high performance composites were focused on iron and its alloys [2]. Fe matrix composite are widely used in a variety of applications where excellent wear and corrosion resistance is required. The significant interest in Fe based composites is developing wear resistant materials by addition of reinforcing hard ceramic particulates [4]. Particles used to reinforce the composite include oxides (Al2O3, Zr2O3, Y2O3), nitrides (TiN) and carbides 65

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(TiC, WC, SiC) [2,3]. The incorporation of a reinforcing agent might further modify the reaction in the composite and improve the overall properties [4-6]. When the reinforcing agent is SiC, the structural modification of pure iron is obvious, if the conditions of the experiments lead to decomposition of the particulate (or fiber) and the dissolution of C and Si in the matrix. The current interest in these composite systems come from the study of reinforcement material that increase hardness to enhance wear resistance. In this study, different compositions of reinforcement material were added to the composite systems to provide an improved understanding of the microstructure and the mechanical properties.

EXPERIMENTAL METHODS This research used composites made by Fe powder, Co powder and silicon carbide (SiC) particle. Fe act as matrix materials with the addition of Co as alloying element. Fe matrix composites containing 11 wt% Co was used for the present study. Powder mixtures of Fe-Co, containing 0, 5, 10, 15 and 20 wt% SiC as reinforcement materials were mixed by powder metallurgy technique. The composite was fabricated via powder metallurgy method, which consists of mixing, compaction and sintering processes. The powder was mixed for 2 hours and compacted to cylindrical shape at 250 MPa. Samples were sintered for 2 hours at 900oC with 10oC/minute heating rate in argon atmosphere. The influences of reinforcement material on the sintered samples were characterized in terms of microstructure and hardness test. Microstructure identification was examined by optical microscope (OM), scanning electron microscope (SEM) and energy dispersive X-ray (EDX). Vickers microhardness test was used to measure hardness value.

RESULTS AND DISCUSSION Microstructural analysis Optical micrograph of Fe-Co metal matrix composite reinforced with different wt% of SiC particle synthesized via powder metallurgy method were shown in Figure 1. The presence of reinforced particles were clearly observed for samples with 5, 10, 15 and 20 wt % SiC [Figure 1 (b) – (e)]. While Figure 1 (a) contain only Fe-Co metal matrix without the SiC. Microstructure observation revealed a well distributed SiC particulates (about 20 m size) around the Fe matrix region. SiC particles appear to be bonded well with the matrix. However, the presence of Co is isolated at the matrix phases. To identify the distribution of Co, EDX analysis was done to reveal the existing element in the composite. Figure 3 (a) shows EDX pattern for overall image analysis as in Figure 2. Figure 3 (b) and (c) shows the EDX pattern for spot 1 (at SiC particle) and spot 2 (at matrix phase). Overall image analysis showed the existence of Si, C, Fe and Co. Whereas, at spot 1, the EDX analysis clearly showed Si peak detected on the SiC particles. For spot 2, the EDX analysis detected Fe and Co in the matrix phase. For further identification of the distribution of Co, mapping analysis for SEM image for 20 wt% SiC sample was done as shown in Figure 4 (a). The analysis showed Si distribution (Figure 4 (b)) as the top color remark at vertical left-side image. Note the higher element detected which is white and pink color. For matrix phase identification, the analysis shows the Fe and Co distribution along the matrix proved co-exist of these materials as shown in Figure 4 (c) and (d). The distribution of Fe can be seen through the pink color along the matrix phase. From this 66

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analysis, Co particles were identified based on red color distribution that co-exist with the Fe particles at the matrix phase. The different composition of Fe and Co were seen because of the higher percentage of Fe that is 69 wt% compared to 11 wt% Co. Microhardness test The influence of reinforcement material on the microhardness of composite Fe-Co was shown in Figure 5. The hardness increased with the increasing of SiC composition. It is observed that the highest value of Vickers hardness recorded at 20 wt% SiC which is 192.8 HVN. Whereas the lowest hardness value recorded at 0 wt% SiC that is 69.2 HVN. There was a slight decrease of the hardness value at 10 wt% SiC compared with the 5 wt% SiC. SiC

Fe-Co matrix

pull out

(a)

(b)

SiC Fe-Co matrix

Fe-Co matrix

SiC

(c)

(d)

SiC

Pores

(e) Figure 1: Optical micrograph of Fe-Co composites with; (a) 0 wt%, (b) 5 wt%, (c) 10 wt%, (d) 15 wt%, (e) 20 wt% of SiC. (Magnification 600X) 67

JOURNAL Of NUCLEAR And Related TECHNOLOGIES, Volume 6, No. 1, Special Edition, 2009

Figure 2: SEM micrograph of Fe-Co/SiC composite.

(a) Overall image

(b) Spot 1 Figure 3: EDX pattern for Fe-Co/SiC composite

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JOURNAL Of NUCLEAR And Related TECHNOLOGIES, Volume 6, No. 1, Special Edition, 2009

(c) Spot 2 Figure 3: EDX pattern for Fe-Co/SiC composite

(a)

(b)

(c)

(d)

Figure 4: SEM micrograph for Fe-Co composite with 20 wt% SiC (a) overall image for analysis, (b) Si distribution, (c) Fe distribution and (d) Co distribution. 69

JOURNAL Of NUCLEAR And Related TECHNOLOGIES, Volume 6, No. 1, Special Edition, 2009

Hardness Vickers Number (HVN)

250 200 151,7 150

192,8

115,2

100

100

69,2

50 0 0

5

10

15

20

25

SiC (w t%)

Figure 5: Effect of hardness Vickers number on Fe-Co composites

CONCLUSION Fe-Co matrix reinforced with SiC particle has been studied. Reinforcement material greatly influenced the properties of Fe-Co composites produced. The composite with 20 wt% SiC showed the highest hardness value that is 192.8 HVN. However, for SEM micrograph, Co particles cannot be seen in the matrix phase. The verification of the particles is proven by the EDX mapping analysis done to the composite system.

REFERENCES [1] Yamaguchi, K., Takakura, N. & Imatani, S. (1997). Compaction and Sintering Characteristics of Composite Metal Powders, Journal of Materials Processing Technology, vol. 63, pp. 364-369. [2] Pagounis, E. & Lindroos, V. K. (1998). Processing and Properties of Particulate Reinforced Steel Matrix Composites, Materials Science and Engineering, vol. A246, pp. 221-234 [3] Sakamoto, M., Liu, H. N., Nomura, M. & Ogi, K. (2001). Tribological Stability Of Al2O3 Short Fiber Reinforced High Cr Cast Irons, Wear, vol. 251, pp. 1414-1420. [4] Pelleg, J. (1999). Reactions in the Matrix and Interface of the Fe-SiC Metal Matrix Composite System, Materials Science and Engineering, vol. A269, pp. 225-241. [5] Tang, W. M., Zheng, Z. X., Ding, H. F. & Jin, Z. H. (2002). A Study of the Solid State Reaction Between Silicon Carbide and Iron. Materials Chemistry and Physics, 74, p. 258264. [6] Hunt, W. H. (2000). Particulate Reinforced MMCs, Comprehensive Composite Materials, Elsevier Science Ltd, vol. 3.26, pp. 701-715.

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