Abstract
The Ni-20 at.% Mo alloy has an order-disorder critical temperature of 1141 K (868[ddot]C). The disordered phase α can be retained by quenching and in this condition samples were cold worked by swaging 43% reduction in area, then aged at 1123K (850[ddot]C) and 973 K (700[ddot]C) for up to 172800 s (48 h). The kinetics of the disorder-order (α to β) transformation has allowed an examination of the interaction of recrystallization and ordering, which was followed by micro-hardness measurements and transmission electron microscopy observations. At 1123 K, the α recrystallized with accompanying softening, then ordered domains (β phase) formed with an accompanying sharp increase in hardness. The hardness began to decrease as the domains increased in size. However, some deformed material was still present after 48 h. At 973 K, the deformed α first changed to deformed β, with a considerable increase in hardness. Then recrystallized β domains formed in the deformed β, and eventually the hardness began to decrease as the domains became large. It was also found that recrystallization in the deformed β was considerably retarded compared to that in deformed α. The general difference in the behaviour at the two temperatures is consistent with the stored energy of cold work being greater than the free energy change of the disorder-order transformation at 1123 K, whereas the opposite effect is found at 973 K.