High-temperature fracture behavior of an α /(3 Titanium alloy manufactured using laser powder bed fusion

The room and high temperature (up to 600 degrees C) mechanical properties, with emphasis on the fracture toughness and fatigue resistance, of an alpha/(3 (3 titanium alloy that was additively manufactured using the laser powder bed fusion (LPBF) technique were evaluated in the as-printed (alpha' ' lath martensite with negligible (3 phase content) and heat-treated (alpha/(3 (3 structure with a significant volume fraction of the (3 phase) states for critically examining the (3 phase's role in the fracture and fatigue behavior (given the significantly higher diffusion rates of various species in (3 compared to alpha). Experimental results reveal that the heat-treated sample exhibits superior ductility and fracture initiation toughness at elevated temperatures, compared to the as-printed sample, due to the presence of (3 ligaments in the former. They also prevent strain localization along the prior (3 grain boundaries, and their absence in the as-printed state leads to cracking along those boundaries. While the fatigue crack growth (FCG) rates in both the as-printed and heat-treated samples deteriorated with increasing temperature, the threshold for FCG generally increased, which is attributed to creep-induced crack tip blunting. Moreover, a double Paris exponent phenomenon is observed for the heat-treated sample at 300 degrees C, attributed to the hydrogen-assisted crack growth, with (3 phase providing an accelerated diffusion pathway. Overall, the experimental results and their analyses illustrate the intricate relationship between creep, hydrogen diffusion, and the (3 phase in dictating the fracture behavior of LPBF alpha/(3 (3 titanium at elevated temperatures.