Surface integrity of biodegradable orthopedic magnesium–calcium alloy by high-speed dry face milling

Biodegradable magnesium–calcium (MgCa) implants have the ability to gradually dissolve and be absorbed in human body after implantation. Since the implant surface is in direct interaction with body fluids, surface integrity of MgCa implants are key factors influencing degradation rate of the biodegradable implants. Machining is often very necessary to make geometric features of implants. The effects of process parameters in dry high-speed face milling of MgCa0.8 (wt%) alloy on surface integrity characteristics, i.e. surface topography, surface roughness, microstructure, microhardness, and residual stresses, are investigated in this study. Polycrystalline diamond inserts are used to avoid material adhesion in milling MgCa alloy. High cutting speeds of up to 2,800 m/min and a broad range of feed and depth-of-cut values are selected to cover the regimes of finish and rough cutting. Average roughness value of 0.4 μm and shallow strain hardened depths are achieved. Little change of grain size can be observed in the near surface even for very slow feed value of 0.05 mm/rev. The surface residual stresses are measured to be highly compressive.