In this investigation, weld heat-affected zone (HAZ) structures of gamma titanium aluminide alloys were interpreted in light of knowledge about solid-state phase transformations, to gain a better understanding of phase transformation kinetics.; CO{dollar}sb2{dollar} laser welds were generated on three cast, HIPed, and heat treated alloys, Ti-47Al-2Cr-2Nb, Ti-48Al-2Cr-3Nb, and Ti-47Al-2Cr-3Ta, with weld heat inputs between 5.9 kJ/cm and 0.8 kJ/cm and preheats of up to 400{dollar}spcirc{dollar}C. Controlled thermal cycles were performed using the Gleeble{dollar}spcircler{dollar} system to obtain information on solid-state phase transformations. Metallographic characterization and microhardness measurements were performed on as-welded specimens, postweld heat treated weld specimens, and thermally-cycled specimens.; Welds without cracking were produced in all three alloys at intermediate heat inputs. Welds with the highest heat input exhibited centerline solidification cracking while welds with the lowest heat inputs without preheat exhibited transverse solid-state cracks.; The far-HAZ for each alloy had a predominantly duplex structure, with laths subdividing equiaxed gamma grains and at gamma grain boundaries, and blurred contrast in the lamellar colonies. Both features were products of the early stages of alpha growth on heating, indicating that the far-HAZ did not transform to single phase alpha. In higher heat input welds the near-HAZ for each alloy was made up of fine {dollar}alphasb2{dollar} + {dollar}gamma{dollar} in lamellar, Widmanstatten, and acicular/feathery morphologies, due to complete transformation to alpha on heating and then transformation to {dollar}alphasb2 + gamma{dollar} structures on cooling. In the tantalum-bearing alloy, colonies of short {dollar}alphasb2{dollar} platelets enriched in chromium and tantalum were seen near the fusion boundary. Weld with lower heat inputs, with and without preheat, exhibited progressively finer transformed HAZ structures. The HAZ structure for 0.8 kJ/cm welds was tentatively identified as massively transformed gamma.; Postweld heat treatment produced near-gamma structures, with {dollar}alphasb2{dollar} at the gamma grain boundaries. Hardnesses of fusion zone and HAZ were reduced by postweld heat treatment, to close to base metal levels.; Gleeble{dollar}spcircler{dollar} thermal cycles reproduced all weld HAZ structures except massive gamma. Time-temperature-transformation diagrams for the transformation to alpha on heating were generated for each alloy. Microhardness increased with cooling rate for both partially-transformed and fully-transformed specimens.
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