Phenomenological observations of lamellar orientation effects on the creepbehavior of Ti-48at. %Al PST crystals

The anisotropy in creep behavior of a PST crystal was examined using crysta ls of the composition Ti-48Al in three different orientations, phi = 0 degr ees, 45 degrees and 90 degrees, in the temperature range of 700-815 degrees C. In addition, a fully lamellar Ti-48Al polycrystal of similar lamellar s pacing was also tested under identical conditions for comparison. Significa nt anisotropy was observed at all the three temperatures of teal. In both p rimary and secondary stages, the 0 degrees PST material was consistently th e strongest and the 45 degrees the weakest, with the polycrystal behaving m uch like the 45 degrees PST crystals. The anisotropy could not be rationali zed based on either Schmid factor differences or alpha(2) anisotropy. The b eneficial effects of orientation are observed to be similar to those of all oying additions of C or Si. It is anticipated that fully lamellar textured polycrystals will be significantly superior to polycrystalline materials ha ving a random grain orientation in both primary and secondary-stage creep b ehavior. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Lid. Ali rights reserved.