The temperature dependence of the long-range order parameter of Ni3Al

Abstract

The macroscopic yield stress of Ni3Al increases rapidly with temperature, reaching a maximum at about 700°C. Such anomalous behavior has been observed in other ordered alloys which undergo partial disordering with increasing temperature, e.g. Cu3Au. The long-range order parameter, S, of stoichiometric Ni3Al powder was measured over the temperature range 25°C to 1000°C and great care was taken to ensure a fine particle size and thus avoid extinction effects. The results of this study showed that, in Ni3Al, S remains constant at about 0.93 over the entire temperature range investigated. This means that theories relating the strength of ordered alloys to S are not applicable to Ni3Al.