Grain growth in heat affected zone of fine grained titanium alloy

Grain growth in coarse grained region of fine grained titanium alloy welded joint was studied, and influences of grain coarsening on microstructure transformation and microhardness along the welding seam were measured during gas tungsten arc welding of fine grained Ti-6Al-4V with equiaxed crystal. The results showed deviation of β transus temperature induced by grain sizes of parent metal resulted in less grain growth of coarse grained region in fine grained Ti-6Al-4V than in conventional Ti-6Al-4V. Continued reduction in nucleation of α′ martensite resulted in significant growth directivity of α′ plates in coarse grained region of fine grained Ti-6Al-4V. Moreover, thickening of martensitic lamina at prior β boundaries and lengthening of martensitic plates within grains occurred with increasing grain coarsening in coarse grained region. Compared with conventional Ti-6Al-4V alloy, there was no softened zone in the heat affected zone of fine grained Ti-6Al-4V with grain coarsening in coarse grained region.