Effects of strain-rate and ageing at 573 and 973 K on the mechanical (compressive) behaviour of <110> oriented ('soft') NiAl single crystals with and without microalloying additions of Ti, Zr, and Hf .2.

The effects of impurity gettering on the mechanical behaviour of NiAl have received extensive attention recently. The present work was directed at static and dynamic strain ageing phenomena and strain-rate sensitivity minima, which are supposed to be related to the dislocation-impurity interactions, for <110> oriented NiAl single crystals with microalloying additions of Ti, Hf and Zr as getters (0.1 at.%). The influence of ageing at 573 and at 973 K on compressive properties and microhardness was also investigated. The gettering effects were found to be less pronounced for NIAl + Ti and more pronounced for NIAl + H+ and NIAl + Zr, and the gettering effects lead to marked changes in the strength and ductility behaviour after ageing at 973 K as well as static strain-ageing at 573 K, and to strain-rate sensitivity. The observed effects are believed to be due to the formation of precipitates containing Ti, Hf, or Zr, their coarsening during ageing, and interactions of dislocations with either precipitates and/or solute atoms and interstitials. (C) 1996 Elsevier Science Ltd.