Mechanical and Microstructural Analysis on the High Temperature Deformation of Gamma TiAl Alloy

摘要

It is aimed in this study to investigate the high temperature deformation mechanisms of two-phase gamma titanium-aluminum alloy in view of the inelastic deformation theory and to quantify the relative contribution of each mechanism to the overall deformation. The influence of y/a2 volume fraction on high temperature deformation behavior and the preferable cavity initiation sites have also been studied. For this purpose, a series of load relaxation tests and tensile tests have been conducted at temperatures ranging from 800 to l050 deg C. In the early stage of the deformation, (as in the load relaxation test) flow curves of the fine-grained titanium-aluminum alloy are well fitted with the combined curves of grain matrix deformation and dislocation climb. The evidence of grain boundary sliding has not been observed. However, when the amount of deformation is large (exceeding 80%), flow curves change its shape indicating that other deformation mechanism operate at this stage. It is identified as grain boundary sliding resulted from dynamic recrystallization. The activation energy values for grain matrix deformation and dislocation climb have been obtained from constitutive parameters analysis. Calculated values for QGMD and Qdisl. climb are 3l9kJ/mol, and 386 kJ/mol, respectively Qdisl.climb is found to be similar to that for self-diffusion of Aluminum in titanium-aluminum or in Ti3Al. With the increase in the volume fraction of a sub 2-phase, the flow stress for grain matrix deformation increase because a sub 2-phase is considered as hard phase which acts as barrier for dislocation movement. The fact that the frequency of cavity initiation at a sub 2 phase is 8 times as high as that of a sub 2/y supports the above interpretation.