Uniaxial Compression Properties and Compression Fatigue Performance of Selective Laser Melted Ti–6Al–4V Cellular Structure

The selective laser melted (SLM) Ti–6Al–4V cellular solid is a promising material in biomedical and other applications. The mechanical properties of the SLM Ti–6Al–4V cellular material are predominantly controlled by the design of the cellular structure. The objective of this study was to investigate the uniaxial compressive properties and compressive fatigue performance of the SLM Ti–6Al–4V cellular solid with a new cuboctahedron unit cell reinforced by four diagonal struts and two horizontal struts along the X and Y axes. The influences of hot isostatic pressing (HIP) on the various mechanical properties were also examined. The results showed a smoother stress–strain curve and fewer stress oscillations in the HIP specimen than in the SLM specimen. The HIP process slightly decreased the yield strength of the SLM sample from 55 to 52 MPa. Under uniaxial compressive stress, the SLM and HIP specimens exhibited layer-by-layer fracture and diagonal shear fracture, respectively. Furthermore, the HIP treatment significantly increased the fatigue performance and improved the fatigue endurance ratio at 106 cycles from 0.15 to 0.35. The HIP treatment contributed to several positive effects, including phase transformation from brittle α′ to α + β, the elimination of strut porosity and residual stress, an increase in lath size, and a better combination of strength and ductility, thereby improving the fatigue performance. The effects of stress mode on the fracture mechanism were also clarified using in situ observation in combination with digital image correlation.