Fusion zone microstructure and fatigue crack growth behaviour in Ti-6Al-4V alloy weldments

TLDR: In this paper, the fatigue crack growth resistance of α-β titanium alloys can be altered by microstructural modification during welding, the fusion zone microstructure depends on cooling rate.

Abstract: The fatigue crack growth resistance of α–β titanium alloys can be altered by microstructural modification. During welding, the fusion zone microstructure depends on cooling rate. In the present work, the alloy Ti-6Al-4V was welded over a range of heat inputs, using electron beam and gas tungsten arc welding. The weld microstructure varied from predominantly martensitic under rapid cooling conditions to a mixture of martensite and diffusional products on slower cooling. Post-weld heat treatment resulted in a basketweave α–β aggregate that coarsened with temperature and time. In all welded and heat treated conditions, the fusion zone exhibited a fatigue crack growth resistance superior to that of the base material, which was in part attributed to the lamellar microstructure of the fusion zone. Welding residual stresses also played a beneficial role in the as welded condition. Post-weld heat treatment eliminated the advantage resulting from the welding stresses but not that as a result of microstructure.