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

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 beta 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 alpha phase, existing in the beta 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 alpha phase and a beta phase. In the water quenching, the beta phase is transformed into a lamellar structure of secondary alpha phase and beta 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 alpha phase.

Automated summary

The plastic elongation of Ti-6Al-4V alloy samples is successfully improved from 1.0% to 3.2% through heat-treatment. The formation of acicular alpha phase, which is harmful for the ductility, is suppressed by quenching and effectively eliminated. Moreover, the transformation of beta phase into a lamellar structure in the water quenching process contributes to the improved ductility.