Hybrid surface treatment for improving mechanical and surface properties of AISI 316L stainless steel

Failures of osteosynthesis plate are often dealing with overloading and fatigue fracture. Efforts have been made to improve the strength of the plate. In addition, surface roughness is also a matter of concern which relates to biocompatibitlity of the plate. In this study, a hybrid surface treatment consisting of surface mechanical attrition treatment (SMAT) and electropolishing is used to improve the strength and surface properties of AISI 316L stainless steel; a typical biomaterial used for osteosynthesis plate. The SMAT was performed using 250 steel balls with diameter of 4.36 mm for 0 - 20 minutes. The following electropolishing treatment was conducted after the SMAT for 0 - 20 minutes. The subsurface microhardness and surface roughness were measured to evaluate the change in mechanical and surface properties of AISI 316L after the treatment, respectively. The result shows that the SMAT enhanced surface microhardness from Hv = ±1.4 GPa to ±2.9 GPa, but remained to yield a rough surface (R_a = ±1 μm). The roughness and subsurface microhardness decreased from R_a = ±1.0 μm to ±0.1 μm and from Hv = ±2.9 GPa to ±2.2 GPa, respectively. In conclusion, the hybrid surface treatment in this study is able to improve both surface and mechanical properties of AISI 316L stainless steel.