A comparative study of microstructure and tensile properties of Ti2AlNb joints prepared by laser welding and laser-additive welding with the addition of filler powder

Abstract

The influence of the addition of filler powder on the microstructure and properties of laser-welded Ti2AlNb joints was comparatively investigated using scanning electron microscopy, transmission electron microscopy, electron back scattered diffraction, and tensile tests. The heat affected zone (HAZ) of laser-additive-welded joints was divided into B2, B2 + α2, and B2 + α2 + O — three regions with increasing distance from the fusion line. The HAZ of laser-welded joints could only be divided into two regions, viz., B2 + α2 and B2 + α2 + O. The microstructure of the fusion zone was composed of a single B2 phase for both laser welding and laser-additive welding. Columnar grains were observed in the fusion zone of laser-welded joints, while the B2 grains in the fusion zone of laser-additive-welded joints were basically equiaxed. A misorientation angle distribution analysis showed that the fraction of high-angle grain boundaries of laser-additive-welded joints was higher than that of laser-welded joints. The addition of filler powder promoted heterogeneous nucleation during solidification in laser-additive welding. Following tensile tests at room temperature, failure tended to occur in the fusion zone of the laser-welded joints and in the HAZ of the laser-additive-welded joints. The laser-additive-welded joints exhibited better tensile properties because of the higher Mo content as well as the equiaxed microstructure of the fusion zone.