Integrating HIP and homogenisation heat treatment and its effect on the workability of a conventional peritectic TiAl alloy

Abstract

The aim of this study was to understand how consolidation and homogenisation, as well as the possibility of integrating the two processes, influences the pre-compression microstructure and subsequent compression behaviour of an industry accepted, peritectic solidifying titanium aluminide ingot alloy; 45XD.This study differs from existing work with its emphasis on understanding the effect of integrating consolidation and homogenisation on workability, as well as how these processes influence the pre-and post-compression microstructure individually. This was assessed by the material's strain rate sensitivity in primary and secondary compression. The target microstructure was identified from the literature as being capable of a strain rate sensitivity of ≥0.3.The results presented here show that it is possible to integrate the consolidation and homogenisation stages, and this proved beneficial, namely achieving a high lamellar content and elementally homogeneous microstructure presented prior to compression. Subsequent deformation generated high values of dynamic recrystallisation fraction and globularisation returned upon primary compression, and the highest strain rate sensitivity at secondary compression, in comparison to material processed by the traditional approach. This is thought to be due to pressure and temperature during the integrated process reducing both segregation, seen through casting, and so the B2/β0 content compared to consolidated material. The integrated consolidation and homogenisation approach also prevented the grain growth seen in the traditional route; this is anticipated to be due to the two slow cooling stages involved in the traditional process rather than the effect of isostatic pressure.