PHASE FORMATION AND STABILITY IN THE PSEUDOBINARY.

In order to study the formation of phases and their thermal stability, DSC (differential scanning calorimetry), x-ray diffraction, and optical microscopy were performed simultaneously in the Ni//3Al-Ni//3V pseudobinary alloy system. For the alloy series represented by Ni//3(Al//xV//1//0//0// minus //x), a tetragonal DO//2//2 phase was found to form for x less than 10, and a cubic L1//2 phase for x greater than 75 at room temperature. For 10 less than x less than 75, the DO//2//2 and L1//2 phases were found to coexist. Contrary to some theoretical expectations, no complex ordered equilibrium phases formed in this alloy system at any intermediate composition between Ni//3Al and Ni//3V. Measurements of the order-disorder transition temperature, T//c, by DSC, and the associated details of the phase transformations and stability are discussed.