Effects of graphite on wear and corrosion behaviour of SiC _p-reinforced copper matrix composites formed by hot pressing

The wear and corrosion properties of SiC_p/graphite reinforced copper metal matrix composites (MMCs) fabricated by hot pressing have been evaluated. Electron microscopic studies were conducted to clarify the micromechanisms of wear and corrosion. The experimental results indicate that the hardness and wear loss increase with increasing SiC_p content but decrease with increasing graphite content. In particular, the wear loss decreases with increasing graphite up to a content of 5 vol.-% then remains approximately constant as the graphite content is further increased to 7-5 vol-%. The material porosity of the composites increased with the content of foreign particles (SiC_p and/or graphite). The composites were immersed in an aqueous solution of 3-5 wt.-%NaCl at pH 6-7 for potentiodynamic and corrosion rate measurements. Pure copper exhibited the best corrosion resistance. The Cu/SiC_p composite showed lower resistance, and the Cu/SiC_p/graphite composite had the lowest resistance to corrosion. The poor corrosive properties of the composites were the result of galvanic and crevice corrosion, which were influenced by residual stress/strain and differences in electrochemical potential between the additions (SiC_p and/or graphite) and the copper matrix. Furthermore, the weight loss due to corrosion increased with increasing SiC_p and graphite content.