High-temperature Tensile Behavior of Laser Welded Ti-22Al-25Nb Joints at Different Temperatures

The high-temperature tensile behavior of laser welded Ti-22Al-25Nb (at%) joints was investigated at 500, 650, 800, and 1 000 °C. The temperatures for tensile tests were selected according to the phase transformation sequence of Ti₂AlNb-based alloys. At temperatures lower than the B2+O phase field (500 °C) and higher than the B2+O phase field (1 000 °C), the joints fracture in the base metal in ductile fracture mode. By contrast, the joints exhibit obvious high-temperature brittleness in the B2+O phase field (650 °C and 800 °C). Heat treatments were conducted with respect to the thermal history of tensile specimens. Intergranular microcracks along the grain boundary of B2 phase are found in the fusion zone after the heat treatments at 650 °C and 800 °C. The high-temperature brittleness at 650 °C and 800 °C is attributed to the B2→O transformation along the grain boundary. The stress concentration caused by the volume change of B2→O transformation also contributes to the high-temperature brittleness of laser welded Ti-22Al-25Nb joints.