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. (C) 2010 Elsevier B.V. All rights reserved.