Effect of thermomechanical processing on microstructure evolution and mechanical properties of metastable β Ti–5Al–5V–5Mo–3Cr alloy

Abstract

Two distinct thermomechanical processing (TMP) schedules are applied to as-cast Ti-5553 alloy pancakes, to optimize its microstructure and mechanical performance. While TMP-I involves 40 % thickness reduction via forging, TMP-II employs rolling with 20 % thickness reduction. Typical bimodal microstructures with nearly similar sizes, distributions, and morphologies for the primary αp grains and colonies of secondary αs and β are noted to generate for both TMP-I and TMP-II. Certainly, rolling for only half the extent of that used for forging, appears ideal and economical for obtaining the targeted microstructure. Interestingly, similar and improved localized hardness values with respect to as-cast alloy, are obtained for bimodal microstructure, generated through both the TMP schedules. However, indentation size effect is noted to be nominally lower for the rolled alloy, thereby proving its suitability for large-scale application. Global behavior assessed through tensile tests also shows that bimodal microstructures obtained through forging or rolling leads to higher strengths, toughness and ductility, as compared to as-cast counterparts. This is primarily owing to non-uniform strain distribution in the as-cast alloy, resulting to crack initiation and failure, as revealed through digital image correlation-based study. Overall, TMP employing rolling with reduced deformation in particular appears beneficial for the mechanical property improvement of the alloy.