Rate dependent tension-compression-asymmetry of Ti-61.8at%Al alloy with long period superstructures at 1050 °C

Abstract

Al-rich TiAl alloy system has recently become a focus of interest due to its higher oxidation resistance, 20% lower density and higher (200°C more) operating temperature application possibility over conventional Ti-rich TiAl alloys. Tension-compression asymmetry of such type of high temperature material is an integral part of modern engineering problems. Rate dependent asymmetric phenomena of such alloys is specially important at high homologous temperature because of the appearance of one or more long period superstructures. However, micromechanical modeling endeavor of Al-rich family has not been attempted so far. In this work, we have presented two internal variable based phenomenological crystal viscoplasticity modeling approach for predicting rate dependent tension-compression asymmetry of single crystal like lamellar Ti-61.8at%Al binary alloy at hot compression state (1050°C) by employing finite strain and finite rotation framework. Our material parameters were based on calibrating three different sets of compressive stain rate controlled plasticity data in two lamellar directions. Based on the set of identified material parameters we have predicted qualitatively the evolution of tension compression asymmetry of this alloy. It is found that tension-compression-asymmetry evolution is anisotropic and highly pronounced throughout the deformation process influenced by the lamellar morphology and long period superstructures. Slip system level operative stresses show that the slip domination and activity, more specifically, major contributing systems are different in tension and compression.