Phenomenological observations of lamellar orientation effects on the creep behavior of Ti–48at.%Al PST crystals

Abstract The anisotropy in creep behavior of a PST crystal was examined using crystals of the composition Ti–48Al in three different orientations, φ =0°, 45° and 90°, in the temperature range of 700–815°C. In addition, a fully lamellar Ti–48Al polycrystal of similar lamellar spacing was also tested under identical conditions for comparison. Significant anisotropy was observed at all the three temperatures of test. In both primary and secondary stages, the 0° PST material was consistently the strongest and the 45° the weakest, with the polycrystal behaving much like the 45° PST crystals. The anisotropy could not be rationalized based on either Schmid factor differences or α 2 anisotropy. The beneficial effects of orientation are observed to be similar to those of alloying additions of C or Si. It is anticipated that fully lamellar textured polycrystals will be significantly superior to polycrystalline materials having a random grain orientation in both primary and secondary-stage creep behavior.