Fatigue life dispersity and distribution characteristics of laser direct energy deposited Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy

• Fatigue origin and life distribution of AM alloy are affected by internal quality. • Fatigue life dispersion is attributed to the surface and subsurface pore origins. • Two competition effects of origin modes highly affect fatigue life distribution. • P-S-N curves based on the Weibull model are suggested in engineering applications. Additive manufactured titanium alloys exhibit distinct microstructures and internal defects compared to forged alloys. This has a significant impact on its fatigue failure behavior and fatigue life distribution. Fatigue life dispersity and distribution characteristics of laser direct energy deposited Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy were investigated by a relatively large sample fatigue test, fracture morphology characterization, and statistical analytic method. Then, the intrinsic causes of fatigue life dispersity and distribution characteristics were clarified by correlating with fatigue failure origin modes (FFOMs). The test and analysis results indicate that the existence of internal pores significantly influences FFOMs, fatigue life dispersity, and distribution pattern. The FFOMs of microstructure and interior pores have little effect on fatigue life dispersion. In contrast, FFOMs of surface and subsurface pores present a relatively lower fatigue life and are responsible for fatigue life dispersion. Besides, two competitive effects of FFOMs with different applied stress highly affect fatigue life distribution. A bimodal Weibull model is more suitable for describing fatigue life distribution with multiple FFOMs. However, if there is no fast-computing procedure for the parameter estimation of the Bimodal Weibull model, relatively conservative and simple P-S-N curves based on the Weibull distribution model are recommended in engineering applications.