Improvement in microstructure and high-temperature brittleness of laser-welded Ti-22Al-25Nb joints with the addition of TiB2 powder

Abstract

Laser-additive welding using TiB 2 powder with different weight fractions and sizes was applied to join a Ti-22Al-25Nb (at.%) alloy. In the heat-affected zone (HAZ), the O→B2 phase transformation led to the formation of a single B2 phase region. In the case of the joints produced using the TiB 2 powder with a particle size of 4–10 μm, the fusion zone was composed of the B2 and intergranular TiB phases. In the case of the joints produced using the 40–100-μm TiB 2 powder, the B2 and intergranular TiB phases and unmelted TiB 2 particles were formed in the fusion zone as the TiB 2 weight fraction was higher than 6.0 wt.%. When the laser-additive welding was carried out using 3.1 wt.% of the 4–10-μm TiB 2 powder, the fusion zone grain size decreased to 63.1 μm, and the low-angle grain boundary (< 15°) fraction decreased to 10.4 % as compared to the case when autogenous laser welding was carried out. The intergranular TiB phase suppressed the formation of the O phase and improved the tensile properties of the joints at 650 °C. The high-temperature brittleness of the Ti 2 AlNb joints improved significantly with the addition of 3.1 wt.% of the 4–10-μm TiB 2 powder.