Annealing-Induced Hardening in Ultrafine-Grained Ni-Mo Alloys

The influence of Mo alloying on annealing-induced hardening in ultrafine-grained (UFG) Ni is studied. The hardening observed after low temperature annealing is explained by the annihilation of mobile dislocations and a concomitant clustering of the remaining dislocations into low energy configurations. This study reveals that, with increasing Mo concentration, the hardening effect decreases as the Mo solute atoms hinder the annihilation and rearrangement of dislocations. This trend is the opposite to that observed in electrodeposited Ni-Mo alloys where the larger alloying element concentration yields a higher annealing-induced strengthening effect. The difference is attributed to the different deformation mechanisms in UFG and nanocrystalline Ni-Mo alloys.