On the warm temperature strain accommodation mechanisms of Ti–6Al–4V alloy holding different starting microstructures

Abstract

The strain accommodation mechanism of Ti–6Al–4V alloy with different initial microstructure; equiaxed α+β, lamellar α+β, dual phase α+ά, and fully ά martensite was studied in warm temperature deformation regime. Toward this end, a series of tensile tests were performed at room temperature, 400, 500 and 600 °C. The progressive substructure development during tensile deformation of the equiaxed α+β microstructure at 400 °C increased the strain-hardenability (n-exponent) of the material. However, activation of continuous dynamic recrystallization at higher temperature of 600 °C as main strain accommodation mechanisms increases the portion of non-uniform elongation. This was attributed to the resistance against localized deformation and the occurrence of diffused necking. In the case of initial lamellar microstructure, mechanical fragmentation and thermal disintegration of β phase, and globularization of α-phase via boundary splitting mechanism were dominant restoration mechanisms. Martensite reverse transformation and dynamic recrystallization also served as the primary source of softening and strain compensation in dual-phase α+ά initial microstructure. This was led to the development of bimodal/trimodal microstructure representing acceptable balance between strength and ductility. The microstructural evolution in fully ά martensite was relatively analogous to that of α+ά microstructure apart from activation of load transition mechanism. The correlation of strain accommodation capability of each microstructure and tensile formability was discussed in details.

Keywords

• Titanium alloys
• Strain accommodation
• Martensite reverse transformation
• Recrystallization
• Globularization