Room-temperature ductility of Ti–6Al–4V alloy with α′ martensite microstructure

Abstract The microstructures, cold-rolling abilities, and mechanical properties of a Ti–6Al–4V alloy with a α′ microstructure were examined, and compared with these properties in alloys with the (α + β) microstructure. The microstructure of a Ti–6Al–4V alloy solution treated at 1373 K followed by quenching (referred to as 1373 K STQ in the following) exhibits the acicular α′ martensite microstructure. The alloy exhibits the (equilibrium α + α′ martensite) bimodal microstructure when 1223 K solution treatment is carried out followed by quenching (referred to as 1223 K STQ). In contrast, Ti–6Al–4V alloys heat treated at 1373 K or 1223 K, followed by furnace cooling (referred to as 1373 K ST-FC and 1223 K ST-FC), exhibit a lamellar (α + β) microstructure and an equiaxed (α + β) microstructure, respectively. The strength of the STQ specimens was found to be higher than that of the ST-FC specimens. The 1223 K STQ specimen had excellent cold-rolling ability (more than 40% reduction) and higher tensile ductility than those of the ST-FC specimens. The excellent ductility of 1223 K STQ is thought to be due to the constituent phase of the single HCP phase (α′ and α) and the fine equiaxed bimodal morphology. The compositional distribution of the V content enrichment and the decrease in the Al content in the α′ martensitic region during solution treatment at 1223 K should contribute to the excellent ductility. This work therefore suggests a useful method for improving room-temperature ductility by using industrial Ti–6Al–4V alloys with the α′ martensite microstructure.