Deformation induced microstructure and texture evolution in additively manufactured Ti-6Al-4V sheets via friction stir welding

Abstract

Deformation induced via welding often governs the applicability of advanced materials which could either enhance or degrade the mechanical properties. Therefore, this study investigates the deformed microstructure and consequent texture evolution in friction stir welded (FSWed) electron beam printed Ti-6Al-4V plates. While as-additively manufactured alloy exhibited a columnar prior β grain structure along the building direction with equiaxed prior β grains in the perpendicular plane, coarser α needles within prior β grains were observed in the stir zone (SZ) and a bimodal microstructure was observed in the thermo-mechanically affected zone (TMAZ). The highest hardness was obtained in TMAZ, thus deviating from the usual trend of recording the highest hardness in SZ. The FSWed sample exhibited a joint efficiency of 77 %. The reduction is attributed to the presence of tungsten-cobalt rich particles and coarser β grains in the SZ which led to the reduction in hardness/strength or in other words formed a soft zone. A strong texture and variant selection with a significant prevalence of <11 $\bar{2}$ 0>/60° α/α grain boundaries were observed in the as-additively manufactured alloy. In contrast, the FSWed joint displayed random texture with varying intensities across each characteristics zone of FSW, thereby highlighting the influence of cooling rates and deformation on texture evolution. Also, a slight increase in texture intensity and some variant selection was observed at the center of SZ although less pronounced than the as-additively manufactured alloy.