COBALT ALUMINIDE SYNTHESIS BY SHS REACTION AND ITS APPLICATION AS REINFORCEMENT OF COPPER MATRIX COMPOSITES

The porous single-phase CoAl compound powder synthesized by self-propagating high-temperature synthesis (SHS) was used as the reinforcement phase to produce the dense CoAl/Cu (50 wt.% Cu) metal matrix composite by solid-state (SSS) and liquid-phase sintering (LPS), at 750 and 1150 degrees C, respectively. Multiscale microstructure characterization was carried out in terms of X-ray diffraction, scanning and transmission electron microscopy in order to reveal reaction and sintering mechanisms. The results indicate that the LSP conducts to higher relative density of around 98.5% compared with the SSSed case of 95%. During the LSP process, the effective diffusion of molten Cu, promoted by capillary aspiration of the liquid, allows to fully fill the pre-existing pores of the SHSed CoAl to form sub-micrometre sized Cu precipitates homogenously dispersed within the reinforcement particles. The formation of sub-micrometre sized rod-like CoAl precipitates in the Cu matrix is caused by the solution-precipitation mechanism. The microhardness measured in the CoAl reinforcement particles and Cu matrix of the LPSed composite, being higher than those of the SSSed one, is discussed to be associated with the resultant microstructure.