Influence of processing parameter on the microstructure and forming characterizations of Ti-6Al-4V titanium alloy after laser rapid forming processing

Laser rapid forming (LRF) of Ti-6Al-4V (TC4) alloys was experimentally investigated systematically, the influence of the processing parameters, such as laser power, scanning velocity, powder feeding rate, overlaps and single-layer offset along Z axis, on microstructures and forming characterizations were analyzed. The results indicate that columnar prior β grains shorten and coarsen with the increase of laser power P and the decrease of scanning velocity V, finally change to irregular coarsen equiaxed grains. Under the same laser power, the columnar grains become fine and long with the increase of scan velocity. When P/V is larger than 933 W·s/mm, the grains characteristic is equiaxed. There exists a critical overlap for the forming quality. When overlap is 30%, the microstructures present good quality just with a little ill-bonding between the traces near the substrate. If overlap is less than 30%, irregular ill-bonding will occur in the region of adjacent cladding layer in whole LRF parts, otherwise, there is no defect in the whole cladding layers. In addition, when single-layer offset along Z axis is less than the height of single cladding layer, the coarse α laths will be obtained which result from the over reheating of the post deposition layers, and, much larger ΔZ will result in ill-bonding between the cladding layers.