Elevated temperature properties of electron beam welds of an alpha+beta titanium alloy

The effect of base metal microstructure and post-weld heat treatment (PWHT) on the stress rupture creep and high temperature tensile properties of ele ctron beam welds of an alpha + beta titanium alloy, Ti-6.8Al-3.42Mo-1.9Zr-0 .21Si has been evaluated. In the as-welded condition, the stress rupture pr operties of the welds were poor. Stress relieving improved the properties b ut they were still inferior to the base metal properties. Creep strains in the as-welded condition were also large. The poor stress rupture and creep properties in the as-welded condition may be due to a metastable microstruc ture and possible hydrogen accumulation in the heat affected zone (HAZ), th e location of failure. Welds of the base metal in the beta heat treated con dition (beta base welds), with a coarse prior beta grain size at the locati on of failure exhibited superior stress rupture properties and predominant intergranular fracture, while welds of the base metal in the alpha + beta h eat treated condition (alpha + beta base welds) failed in a transgranular m ode. PWHT of alpha + beta base welds with predominant acicular/lenticular a lpha microstructure just below the beta transus temperature exhibited margi nally superior stress rupture strength than the base metal with an equiaxed alpha + lenticular/acicular alpha microstructure. Supertransus PWHT led to poor stress rupture properties due to thick grain boundary alpha, and a th ick and aligned a plate colony structure. High temperature tensile properti es of welds were equivalent to that of the base metal. alpha + beta base we lds with a finer prior beta grain size at the location of failure exhibited superior strength and ductility. Subtransus PWHT resulted in an acicular a lpha microstructure and low ductility. PWHT in the supertransus region resu lted in poor strength and ductility due to coarse and aligned transgranular alpha + grain boundary alpha. (C) 1999 Elsevier Science S.A. All rights re served.