PHASE-STABILITY OF NI-AL SOLID-SOLUTIONS

We have studied the stability of Ni(1-x)-Alx solid solutions at differ ent stoichiometries (x = 0.25 and x = 0.5) via molecular dynamics simu lations of models based on an n-body potential. The face-centred-cubic solid solution with x = 0.25 is stable at room temperature against th e ordering transformation which occurs at T = 360-degrees-C via the ac tivation of vacancy diffusion with a release of a disordering enthalpy of 8 kJ (g-atom)-1. The results obtained from the simulated model sho w an intrinsic instability of the x = 0.5 solid solution which is cons istent with experimental results that have revealed the direct formati on of NiAl (B2) intermetallic phase accompanied by a considerable heat release.