The orientation and temperature dependence of the yield stress of Ni3 (Al, Nb) single crystals

Abstract

The flow stress of Ni3(Al, Nb) single crystals has been measured as a function of orientation in the temperature range 77 to 910 K. While the increasing flow stress behavior is similar to that observed in other Ni3Al-based alloys, the absolute value of the stress was found to be much higher. Also, the effect of orientation changes was to produce much greater changes in the temperature at which the peak flow stress occurs than has been previously observed. The operative slip systems were analyzed by two surface slip trace analysis. Primary octahedral slip was found to be predominant at temperatures below the peak stress temperature, while primary cube slip is prevalent above the peak temperature. The anomalous increase in the flow stress of Ni3(Al, Nb) with increasing temperature is generally consistent with the thermally activated cross-slip of a/2 dislocations from {111} planes onto {100} planes. The cross-slip is shown to be aided not only be the resolved shear stress on the {100} cross-slip plane but also by the stress tending to constrict the a/ Shockley partial dislocations on the primary glide plane.