Fatigue strength dependence on microstructure and defects in Ti-6Al-4V welds

The effect of defects and microstructure on mechanical properties of Ti-6Al-4V welds produced by plasma arc welding (PAW) and tungsten inert gas welding (TIG) was studied. Both types of welds were fatigue tested at 250°C. Weld microstructure, fracture surfaces, crack initiation sites and internal defects such as porosity were studied using optical microscopy and SEM. Also microhardness measurements were performed. The fatigue performance of the welds tested at 250°C was found to be comparable to each other. Fatigue cracks in almost all samples were found to initiate at pores, especially the ones close to the sample surface. Large pores and pores close to the surface were found to have the largest effect on fatigue life. The weld microstructures consisted of coarse prior β-grains