Fatigue performance of laser powder bed fusion manufactured TiB2/AlSi10Mg composite: Experimental investigation and fracture mechanics-based life prediction model for defect tolerance analysis

The fatigue performance of AlSi10Mg composites decorated with nano-TiB2 particles fabricated through laser powder bed fusion (LPBF) was first experimentally investigated at room temperature and it exhibited superior fatigue resistance compared with other LPBF AlSi10Mg alloys and other reinforced AlSi10Mg composites. Then the fractography was examined and a fracture mechanics-based life prediction method was proposed to correlate the critical defect information (size and location) and fatigue life. To assess the crack growth driving force for critical defects, we employed Murakami's concept of the maximum stress intensity factor (SIF). The modification was made to include the effect of specimen cross-sectional geometry and initiation location since Murakami's method would underestimate the maximum SIF in some cases. Meanwhile, the process of small crack propagation was also considered in modeling, and a unified model to describe crack arrest, small crack growth, and long crack growth was established. By inputting information about defect size and location and external loading conditions, the fatigue life could be evaluated and our results demonstrated good estimation within the [1/4,2] scatter band. Furthermore, an unbroken specimen subjected to the highest external loading was examined using X-ray computed tomography (CT) to characterize the defect population. By incorporating the CT statistical results into our life prediction model, outcomes such as non-propagating cracks or small crack growth without leading to ultimate failure could be obtained, which was consistent with CT findings. Concurrently, CT analysis revealed that the detrimental effect of large inner defects could be less significant than that of small surface defects. Therefore, we propose a novel strategy that combines defect size and location to enhance defect tolerance in additive manufacturing (AM) materials.