High-Temperature Deformation Behavior of HCP Alloys -- An Internal Variable Approach

摘要

The high temperature deformation behavior of HCP alloys has been investigated within the framework of an internal variable theory. Various mechanical tests were conducted to this end for AZ31 Mg and Ti-6Al-4V alloys together with microstructure observation. In the first part, a series of load relaxation tests was first performed for AZ31 Mg alloy to obtain overall flow curves, which were then analyzed according to the respective physical mechanisms, viz., the grain boundary sliding (GBS) and the accommodating dislocation glide process as prescribed by the internal variable theory proposed by the authors. Many valuable data were obtained in this way, providing new physical insight as well as a more comprehensive understanding about the superplastic deformation behavior of AZ31 Mg alloy. In the second part of this work, load relaxation and creep tests for hot rolled Ti-6Al-4V alloy have also been conducted to clarify specifically the effect of textures on the deformation behavior of this Ti alloy below 700 deg C and the results were then again analyzed according to the internal variable approach. The values of internal strength variables were found to vary significantly by the textures, but not by the test temperature, while the texture effect was found to decrease at higher temperatures. The effect of texture was also observed to decrease by raising test temperature or by reducing the applied stress in creep tests, suggesting that glide assisted dislocation climb was activated at higher temperature and lower stress.