The influence of initial plastic deformation on microstructure and hot plasticity of α+β titanium alloys

Purpose: Hot deformation behaviour of two-phase titanium alloys is determined depending on microstructure developed in heat treatment and plastic deformation processes. In the paper stereological parameters of microstructure obtained in initial heat treatment and plastic working in the α+β↔β phase transformation range with various forging reduction (ε ≈ 20 and 50%) were determined. Evaluation of the effect of thermomechanical process parameters on hot plasticity of Ti-6Al-4V and Ti-6Al-2Mo-2Cr titanium alloys was performed. Design/methodology/approach: In the research, light and transmission electron microscopy were employed. Digital image analysis methods were used for determination of stereological parameters of microstructure obtained in particular stages of thermomechanical process of Ti-6Al-4V and Ti-6Al-2Mo-2Cr titanium alloys. Hot deformation of thermo mechanically processed titanium alloys was performed in vacuum at the temperature of 850 and 925°C at the strain rates ε = 1·10-2, 1·10-1 and 5·10-1 s-1. Findings: It was found that degree of initial plastic deformation in thermomechanical process considerably affects relative elongation in high temperature tensile test at the lowest strain rate applied (ε = 1·10-2). Research limitations/implications: Developed thermomechanical process enables controlling morphology of microstructural constituents and hot workability of two-phase α+β titanium alloys. Practical implications: Obtaining the demanded operational and technological properties of structural two-phase α+β titanium alloys is related to both the appropriate selection of hot working parameters and preceding thermomechanical process conditions. Originality/value: The effect of heat treatment conditions in thermomechanical process on superplasticity of Ti-6Al-4V alloy was researched previously [1, 2]. In this paper two-phase Ti-6Al-2Mo-2Cr titanium alloy was examined too. Additionally, the influence of a degree of initial deformation in thermomechanical process was analyzed. Hot deformation test were conducted at conditions outside the superplastic range too.