The temperature dependence of the long‐range order parameter of Ni 3 Al

The macroscopic yield stress of Ni 3 Al 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 . Cu 3 Au. The long‐range order parameter, S , of stoichiometric Ni 3 Al 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 Ni 3 Al, 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 Ni 3 Al.