STUDIES ON FUSION ZONE FRACTURE-BEHAVIOR OF ELECTRON-BEAM WELDS OF ANALPHA-TITANIUM ALLOY(BETA)

A study was undertaken to understand the fusion zone fracture behaviou r of electron beam welded alpha + beta-titanium alloy Ti-6.5 Al-3.3 Mo -1.8 Zr and 0.25 Si. The effect of base metal microstructure, the amou nt of heat input and post weld heat treatment cycle on the all-weld te nsile properties and fracture behaviour was investigated in this work. In general, it was found that the tensile strength and ductility of a lpha + beta-base welds are higher than that of the beta-base welds and the difference was attributed to the presence of wider fusion zone gr ains of beta-base welds. The beta-base weld tensile specimens always e xhibited an intergranular fracture mode irrespective of the amount of heat input. The single pass low heat input alpha + beta-base welds fai led by ductile transgranular fracture mode, while high heat input sing le pass welds failed by a mixed mode (intergranular plus faceted) frac ture. In general high heat input welds showed low ductility mainly on account of the strain localization effects at the grain boundary alpha phase. Post-weld heat treatments of alpha + beta-base welds resulted in the improvement of tensile ductility and were associated with trans granular fracture due to the absence of strain localization effects at the grain boundary alpha phase.