The effect of porosity on the fatigue crack growth behavior of selective laser melted TA15 titanium alloy

The effect of porosity defects in selective laser melted TA15 titanium alloy on fatigue crack growth behavior was investigated. Porosity defects were quantified and reconstructed in three dimensions using equivalent diameter (Deq) and sphericity (Psi). Based on the geometric and positional characteristics of the pores, three finite element models were constructed to analyze and discuss the variation of stress intensity factors at the crack tip. Results show that under optimal conditions, the pore diameters are concentrated between 25-50 mu m, while under suboptimal conditions, they range from 50-100 mu m, with pore shapes becoming increasingly irregular as diameter increases. The fatigue crack growth rate (da/dN) shows good agreement with the simulation and experimental results of stress intensity factors, with an error rate of about 5 %. Further analysis reveals that when the equivalent diameter exceeds 200 mu m, the stress intensity factor at the crack tip significantly increases, with 200 mu m being the threshold affecting crack propagation. When sphericity approaches 1, the driving force of the pores on the crack is strongest. The stress intensity factor increases when the pore growth direction is at a smaller angle to the crack, with 60 degrees as the critical threshold. Additionally, when the distance h between the crack and the pore is less than 1 mm, the effects of compressive and shear stresses are enhanced, while the influence diminishes when h exceeds 1 mm.