Influence of spraying conditions on microstructures of Al-SiC p composites by plasma spraying
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I. INTRODUCTION
THE coefficient of thermal expansion (CTE) of particlereinforced aluminum matrix composites can be tailored by changing the type and level of reinforcement to meet different design requirements. Additionally, because of high thermal conductivity and low density, these composites have been considered for novel electronic packaging.[1–5] To meet this application, it is required that the composites must contain a higher volume fraction of reinforcement particles for CTE matching between the composites and electronic components. Plasma spraying is an advanced material-forming technology, and has been widely used to produce various coatings and free-standing near-net shapes of a wide range of materials, including metals, intermetallics, ceramics, and composites.[6] Recently, aluminum matrix composites with particle reinforcements, in the forms of coating and bulk free-standing material, have been also obtained by this process.[7–15] The reinforcements used in the composites include SiC, Al2O3, and TiC particles, as well as short graphite fibers. Iiyuschenko et al.[8] used Al and Al-Si powders mixed with 55 to 75 vol pct SiC or TiC particles as feedstock materials to produce plasma-sprayed Al-carbide and AlSi-carbide coatings. Also, Ghosh et al.[12] studied Al/SiC coatings plasma sprayed from Al-SiC powders, where SiC particle content varied from 20 to 75 pct in volume fraction and from 8 to 37 m in size. It has been reported in the literature that the aluminum composite coatings demonstrate superior wear resistance over conventional aluminum alloys.[10,12] However, information such MANCHANG GUI, Professor, National Laboratory of Advanced Composites, Institute of Aeronautical Materials, Beijing 100095, China, SUK BONG KANG, Principal Researcher, and KWANGJUN EUH, Senior Researcher, are with the Korea Institute of Machinery and Materials, Changwon, Kyungnam 641-010, Korea. Contact e-mail: [email protected] Manuscript submitted July 7, 2003. METALLURGICAL AND MATERIALS TRANSACTIONS A
as the microstructure of sprayed composite coatings or bulk materials and the relationship between the microstructure and spray condition are still limited. In an aluminum-ceramic powder system, melting temperature and other physical properties between metallic aluminum and ceramic differ significantly. Thus, the deposition of the two materials in feedstock should be different during plasma spraying. In the present work, air plasma spraying (APS) was employed to form free-standing composites using two feedstock materials of pure aluminum powders with 55 and 75 vol pct SiC particle. The SiC volume fraction and porosity in the sprayed composites were evaluated for different plasma spray conditions and desirable spray conditions to obtain a maximum SiC volume fraction for each feedstock. The variation of SiC level in the sprayed composites due to varying spray condition and SiC size is explained. The formation mechanism of pores in the sprayed composites is also discussed. The microstructure of the sprayed composites was
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