High Temperature Tensile Deformation Mode and Microstructural Conversion of Ti–6Al–4V Alloy with the (α + α′) Duplex Starting Microstructure

Abstract

Herein this work quantitatively clarifies the effects of the α′ martensite phase and its fraction in the (α + α′) duplex microstructure on high temperature deformation mode of the Ti–6Al–4V alloy. The change in the fraction of α′ martensite region results in the change in deformation behavior complicatedly: cooperative occurrences of continuous dynamic recrystallization from the equiaxed α region and discontinuous dynamic recrystallization from the α′ martensite region affect the deformation mode. This work reveals that discontinuous dynamic recrystallization from the α′ martensite acts as an additional accommodation mechanism, resulting in higher ductility associated with enhanced grain boundary sliding. Specifically it is remarkable at lower strain rates. In addition, the Ti–6Al–4V alloy with an (α + α′) duplex microstructure exhibits lower flow stress value and slight higher ductility than that with an equilibrium (α + β) microstructure, implying that the accommodation mechanism for deformation is effectively activated in the α′ martensite microstructure. This work also clarifies the active deformation modes of the grain matrix deformation associated with dislocation glide and the grain boundary sliding quantitatively, revealing the enhanced GBS with increasing strain for the Ti–6Al–4V alloy having higher fraction of α′ martensite region.

Fig. 5 (a) Relationship between the true stress at ε_p = 0.1 and Z parameter in log–log scale and (b) relationship between the elongation to fracture and Z parameter in log–log scale at temperatures ranging from 700°C to 900°C and strain rates ranging from 10⁻⁴ s⁻¹ to 10⁻² s⁻¹.