AN INVESTIGATION OF THE MECHANISMS THAT CONTROL INTERMEDIATE TEMPERATURE CREEP OF NI3AL

In this study, constant stress creep tests were combined with detailed transmission electron microscopy in order to characterize and explain the intermediate temperature creep properties of Ni3Al. It was observed that octahedral glide, the mechanism associated with the anomalous yielding behavior of this alloy, is exhausted during primary creep. Primary creep does not lead to steady state creep but is instead followed by inverse creep. TEM observations indicate that the Kear-Wilsdorf locks that are formed during primary creep do lead to the exhaustion of octahedral glide, but that given sufficient time and temperature these cross-slipped segments are able to bow out and glide on the cube cross-slip plane. This dislocation generation, and subsequent glide, on the (010) plane is the basis for the observation of inverse creep in this alloy. Dislocation motion on the cube plane is a thermally activated process and as such is able to explain the strong temperature dependence that was observed for the intermediate temperature creep strength of Ni3Al.