Microstructure evolution and mechanical response of a boron-modified Ti-6Al-4V alloy during high-pressure torsion processing

Research was conducted on the microstructural evolution and ensuing mechanical response from high-pressure torsion (HPT) processing of Ti-6Al-4V alloy in the as-cast and beta-forged conditions with and without 0.1 wt% boron addition. The boron addition produces refinement of the prior beta grains and the (alpha+beta) colonies and in-troduces an additional TiB phase but this affects the deformation response and the microstructural evolution only at low strains of 0.5-5 rotations. In the initial condition the orientation of the (alpha+beta) colonies significantly affects the deformation response and leads to differences in substructure formation in both the as-cast and beta-forged conditions. This orientation dependence counts on the initial microstructural differences between the unmodified and the boron modified alloys. At higher strains, there is a similar deformation response and microstructure evolution for all the alloys. The hardness variation with equivalent strain is similar for the unmodified and boron modified alloys in as-cast and beta-forged conditions and represents various deformation regimes in HPT-processing. Strength modelling confirms a simultaneous contribution from microstructural refinement and increased dislo-cation density towards the hardness increment during HPT processing. Overall, the as-cast and beta-forged Ti-6Al-4V-0.1B alloys possess identical deformation response to the beta-forged unmodified Ti-6Al-4V alloy in the initial and intermediate stages. At high levels of straining, all alloys respond in an equivalent manner, thus ruling out any possible effects from additional TiB phase or microstructural refinement for the boron-modified alloys.

Automated summary

This research investigated the microstructural evolution and mechanical response of Ti-6Al-4V alloy under high-pressure torsion (HPT) processing in different conditions. The addition of boron refined the grains and introduced an additional TiB phase, affecting the deformation response and microstructural evolution at low strains. The orientation of the colonies significantly influenced the deformation response and substructure formation. However, at higher strains, all alloys showed similar deformation response and microstructure evolution. The hardness variation and strength modeling suggested that microstructural refinement and increased dislocation density contributed to the hardness increment during HPT processing. The as-cast and beta-forged Ti-6Al-4V-0.1B alloys exhibited the same deformation response as the beta-forged unmodified Ti-6Al-4V alloy in the initial and intermediate stages.