Tailoring of microstructure and mechanical properties of Ti–6Al–4V with local rapid (induction) heat treatment

The evolution of microstructure during local rapid (induction) heat treatment (LRHT) and its effect on the tension and fatigue properties of Ti–6Al–4V with an initial microstructure of fine-grain equiaxed alpha or coarse-grain colony alpha were investigated. LRHT of material with an initial equiaxed condition formed a graded microstructure that varied from a fully transformed one at the surface to a bimodal (equiaxed/transformed) one at the center. After final aging (LRHTA), such a material was characterized by an attractive blend of tension and fatigue properties (UTS = 1285 MPa, elongation = 6.3%, endurance limit 710 MPa). An analysis of the dependence of mechanical properties on the volume fraction of heat-treated material revealed that LRHTA processing to 50% transformed in the critical cross section (from point of view of maximum applied loading) gave a balance of tensile properties similar to those obtained via bulk (100%) rapid heat treatment of Ti–6Al–4V. In contrast, the LRHTA of Ti–6Al–4V with a coarse-grain colony-alpha preform condition required longer heating times to refine the structure and provided only a modest improvement in mechanical properties.

Research highlights▶ A detailed study of the influence of LRHT on the microstructure and properties of Ti–6Al–4V was performed. ▶ LRHT of Ti–6Al–4V yields a microstructure consisting of a radial gradient in beta-grain size. ▶ Such a microstructure is a result of the temperature gradient developed during rapid heating. ▶ LRHTA of Ti–6Al–4V produces an attractive balance of tensile and fatigue properties. ▶ LRHT properties are noticeably better than those obtained with conventional treatments.