Mechanical Anisotropy of Superplastic Ti<sub>3</sub>Al Based Alloy

Abstract

The mechanical anisotropy in super α2 Ti3Al based alloys during low temperature superplasticity are explored. The alloy contains DO19 hexagonal α2 grains ~2.2 μm in grain size uniformly distributed in the ordered BCC β matrix. Although the alloy exhibits superior superplastic elongations over 1000% at 920-1000 o C, the elongation drops appreciably to 600% at 900 o C, 380% at 850 o C and 150% at 750 o C. Mechanical anisotropy is observed, and lower flow stresses and higher tensile elongations are obtained in the 45 o specimen as loaded at 25 to 960 o C. The texture characteristics appear to impose significant influence on the mechanical anisotropy at temperatures below 900 o C (under the dislocation creep condition). At loading temperatures higher than 900 o C (under the superplastic flow condition), the anisotropy effect was less pronounced and the grain orientation distribution become basically random in nature. Rationalizations for the mechanical anisotropy in terms of Schimid factor calculations for the major and minor texture components in the α2 and β phases provide consistent explanations for the deformation behavior at lower temperatures as well as the initial straining stage at higher temperatures.