Ordering and structural transformations in Ni₃Al alloys

Abstract

X-ray diffraction profile studies on the filings of stoichiometric and off-stoichiometric compositions of Ni₃Al alloys, with and without boron additions, were conducted to clarify some of the significant anomalies noticed in the literature. The long-range order parameter was estimated as a function of temperature in all the four alloys from (1 0 0)/(2 0 0) and (1 1 0)/(2 2 0) pairs of reflections. The L1₂ structure appears to attain a maximum stability at about 600 °C, around which temperature its order parameter was close to the theoretical value. Above 600 °C, this structure becomes less stable and there appears to be formation of an additional structure of a lower symmetry.