Fracture-mechanical assessment of the effect of defects on the fatigue life of additively manufactured titanium aluminides

The additively manufactured titanium aluminide alloy TNM-B1 was microstructurally and mechanically characterized in the as-built and the hot isostatically pressed (HIP) condition. Constant amplitude tests were performed at room temperature and 800 °C. Fractographic SEM images were used to identify the fracture-inducing defects. HIP processing significantly reduced the number and size of defects, resulting in improved fatigue strength. By applying the Murakami and Shiozawa approaches, fatigue life was correlated with the local stress intensity factor and could be described as a function of stress amplitude, as well as the size and location of the fracture-inducing defect. A method was developed to quantify the effect of manufacturing defects on fatigue life using local defect-based S-N curves.