EFFECTS OF STRAIN-RATE AND AGING AT 573 AND 973 K ON THE MECHANICAL (COMPRESSIVE) BEHAVIOR 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 direc ted at static and dynamic strain ageing phenomena and strain-rate sens itivity minima, which are supposed to be related to the dislocation-im purity interactions, for <110> oriented NiAl single crystals with micr oalloying additions of Ti, Hf and Zr as getters (0.1 at.%). The influe nce of ageing at 573 and at 973 K on compressive properties and microh ardness was also investigated. The gettering effects were found to be less pronounced for NIAl + Ti and more pronounced for NIAl + H+ and NI Al + Zr, and the gettering effects lead to marked changes in the stren gth and ductility behaviour after ageing at 973 K as well as static st rain-ageing at 573 K, and to strain-rate sensitivity. The observed eff ects are believed to be due to the formation of precipitates containin g Ti, Hf, or Zr, their coarsening during ageing, and interactions of d islocations with either precipitates and/or solute atoms and interstit ials. (C) 1996 Elsevier Science Ltd.