Thermal stability of an Al/Ni3Al composite processed by powder metallurgy

The potential of Al/Ni3Al composites for high-temperature applications, especially when friction is involved, is currently being explored. In this work, the thermal stability of an Al/Ni3Al composite obtained by extrusion of Al and 5 vol% of spherical Ni3Al powder particles was investigated at temperatures up to 500 degrees C. The metal/intermetallic composite proved stable up to 300 degrees C. At higher temperatures, dissolution of Ni3Al particles occurred with formation of concentric layers of Al3Ni and Al3Ni2 phases. The amount of Ni aluminides for each annealing condition was determined by applying a specifically developed mathematical procedure. Dissolution of Ni3Al up to 500 degrees C was found to obey a parabolic-type law with an activation energy of 156 kJ mol(-1). Activation energies for growth of Al3Ni2 and Al3Ni were 209 and 110 kJ mol(-1), respectively, in agreement with the literature. The thermal stability shown by this composite makes it a good candidate for high-temperature applications up to 300 degrees C. (C) 1997 Elsevier Science Limited.