TIG welding and laser welding of boron alloyed Ti-6Al-4V

Paper in proceeding, 2016

TIG welds and laser welds have been performed on cast i) Ti-6Al-4V, ii) Ti-6Al-4V+0.06B, and iii) Ti-6Al-4V+0.11B. The effect of boron on the weld microstructure and microhardness is here presented. In the conventional Ti-64 alloy without boron addition large prior β grains exist in the fusion zone and in the heat affected zone, whereas in the alloys with 0.06 wt% and 0.11 wt% boron the prior β grains are found to be approximately 5 times smaller. In the heat affected zones of the boron doped alloys incoherent TiB precipitates are distributed mainly along the prior β grain boundaries, inhibiting grain growth at elevated temperature and being the main reason for the grain refinement. In the fusion zone TiB precipitates are found in stripes at interdendritic regions. Prior β grains are elongated and their size is refined by boron addition. The microstructure in the fusion zones and heat affected zones consist of fine acicular α. TiB precipitates in the fusion zone restricts the length of individual α laths and the size of α colonies. Microhardness measurements across welds reveal increasing hardness with fine acicular microstructure. Boron addition is not found to have significant effect on microhardness in the welds.