Heterogeneous dynamic restoration of Ti-15Mo alloy during hot compression

TL;DR

This study investigates the deformation behavior of Ti-15Mo alloy during hot compression, revealing that dynamic recovery and recrystallisation decrease with increasing strain rate, and introduces an EBSD-based method to quantify subgrain formation.

Contribution

It provides new insights into the dynamic restoration mechanisms of Ti-15Mo alloy and introduces an EBSD-based method to quantify subgrain size during hot deformation.

Findings

Dynamic recovery is the primary restoration mechanism.

Strain hardening increases with strain rate.

Dynamic recovery and recrystallisation decrease as strain rate increases.

Abstract

Near-beta titanium alloys have shown low Young's modulus and good strength, making them excellent implant candidates. However, their processing using thermomechanical routes in single phase beta region results in heterogeneous microstructures due to high content alloying elements and consequent slow diffusion-controlled processes such as dynamic recovery. This study investigates the deformation behaviour of a Ti-15Mo alloy through hot compression experiments using a Gleeble 3800 device in the single beta domain at strain rates from 0.01 s-1 to 10 s-1, reaching final strains of 0.50 and 0.85 followed by immediate water quench. The findings show that the material presents a low strain rate sensitivity. The flow curves show significant strain hardening before reaching a steady-state regime, particularly at high strain rates. The strain hardening exponent calculations support the effect of molybdenum on retarding softening mechanisms such as dynamic recovery. Electron backscatter diffraction (EBSD) measurements of deformed samples revealed that dynamic recovery is the primary restoration mechanism, with continuous and geometric dynamic recrystallisation evidence. Due to the slow restoration process, we observe the subgrain formation for different deformation parameters. Therefore, we introduced an EBSD-based method to quantify dynamic recovery and subgrain size. We concluded that dynamic recovery and dynamic recrystallisation decrease as the strain rate increases with minimal variation at higher strain rates.