Mechanisms of heat treatment and ductility improvement of high-oxygen Ti–6Al–4V alloy fabricated by metal injection molding

Abstract

Ti–6Al–4V alloy samples with 4000 ppm oxygen are fabricated by metal injection molding. The samples are subjected to a heat-treatment, in which the samples are solution-treated below the β transus and subsequently water-quenched. The tensile tests on the samples indicate that the plastic elongation of the alloy is successfully improved from 1.0 to 3.2% by the heat-treatment. Investigation on the microstructural evolution in the heat-treatment shows that an acicular α phase, existing in the β lamellar structure of the as-sintered samples and harmful for its ductility, is suppressed by quenching and effectively eliminated from the heat-treated samples. Moreover, in the solution treatment, the alloy splits into a primary α phase and a β phase. In the water quenching, the β phase is transformed into a lamellar structure of secondary α phase and β phase with improved ductility. As a result, the improved ductility of the heat-treated samples derives from the plastic deformation of the ductile lamellar structures and the synergic displacement of the rigid primary α phase.