NANOCRYSTRALLINE PHASES IN CU-NI, CU-ZN AND NI-AL SYSTEMS BY MECHANICAL ALLOYING

Nanocrystalline solid solutions and intermetallic phases in Cu-Ni (ent halpy of formation, Delta H-f approximate to 2kJ/mol), Cu-Zn(Delta H-f approximate to-8kJ/mol) and disordered Ni3Al (Delta H-f approximate t o-42kJ/mol) in Ni-Al system formed during mechanical alloying (MA) thr ough conventional continuous diffusive mixing mechanism. In contrast, nanocrystalline ordered NiAl (Delta H-f=-72kJ/mol) and NiAl3 (Delta H- f=-39kJ/mol) formed during MA by a discontinuous additive mixing mecha nism. Ternary additions of Fe and Cr made the as-milled NiAl phase dis ordered, and the alloying mechanism changed over to the continous diff usive mode. (C) 1997 Acta Metallurgica Inc.