The influence mechanism of fractal design method on mechanical properties and corrosion behavior of sheet Gyroid porous structures formed by LPBF

In order to meet the various performance requirements of bone implants, it is necessary to design a porous structure with multi-scale pores. In this paper, a set of 2-level fractal porous structures and 1-level porous structures P80 and P85 were designed based on the sheet-Gyroid porous structure. The influence of porosity and fractal design on the forming quality, mechanical properties and corrosion resistance of the porous structures was investigated. The results showed that the porosity deviation of the 2-level porous structures was in the range of 17.88–20.79 %, which was about twice that of the 1-level porous structures. The elastic gradient of 2-level fractal porous structures varied from 1.654 GPa to 3.636 GPa, the compressive offset strength ranged from 50.9 MPa to 111.5 MPa, and the first maximum compressive strength was in the range of 57.8 MPa to 136.6 MPa, all of which were lower than those of 1-level porous structures with similar porosity, which extended the design range of mechanical properties of porous structures to a certain extent, and was conducive to avoiding the stress shielding effect of implants. Based on the study of mechanical properties of 2-level fractal porous structures, the mechanical properties prediction models were constructed based on the improved G-A model. In addition, it was found that the corrosion resistance of 2-level fractal porous structures was much higher than that of 1-level porous structures, and the corrosion resistance decreased with the increase of porosity. The fractal design of TPMS structure can effectively expand the design space of porous bone implants.