Effect of sandblasting treatment on the microstructure and mechanical properties of Ti-6Al-4V porous radial gradient scaffolds formed by SLM

The radial gradient porous structure conforms to the structural characteristics of natural bone, and its mechanical properties can be improved by adjusting the porosity of the inner and outer layers. However, the high surface roughness of the porous structure formed by selective laser melting (SLM) is source the generation of cracks, and harmful for the mechanical properties. In this work, Gyroid unit cell was employed to design six radial gradient porous structures with porosities ranging from 50 % to 80 %, along with one uniform porous structure. Ti-6Al4V porous structure was prepared by SLM and then sandblasted. The effects of sandblasting on microstructure, compressive properties, deformation behavior and energy absorption were studied. The results show that there are many unmelted powder and layered steps, as well as micro-spherical pores in the as-built porous structure. After sandblasting treatment, the powder particles on the strut surface of the porous structure and the surface defects decrease, contributing to improve the forming accuracy. Additionally, the microstructure becomes finer and denser. The stress–strain curve of porous structure is composed of elastic, plateau and densification stages. The elastic modulus, yield strength and energy absorption of the porous as-built structure are 2.21–7.80 GPa, 54.05–320.40 MPa, and 20.76–94.13 MJ/m³, respectively. After sandblasting, these parameters increase to 2.97–8.58 GPa, 61.71–334.92 MPa, and 20.99–109.69 MJ/m³, respectively. The porous structures both before and after sandblasting exhibited shear failure characteristics. However, the fracture surfaces of the sandblasted structures demonstrated mixed ductile and brittle features, whereas the original structures showed relatively more brittle fracture behavior. Furthermore, the Gibson-Ashby prediction model demonstrates that compressive mechanical characteristics increase with increasing relative density. As a result, sandblasting can increase the strength and toughness of the radial gradient porous structure, making it better suited for bone implant applications.