Surface Integrity of Biodegradable Orthopedic Magnesium-Calcium Alloy Processed by High Speed Machining

Novel biodegradable magnesium-calcium (Mg-Ca) orthopedic implants have the ability to gradually dissolve and absorb into the human body after implantation. The critical issue that hinders the application of Mg-Ca implants is its poor corrosion resistance to human body fluids. A promising approach to tackle this issue is tailoring the surface integrity characteristics of the orthopedic implants to get an appropriate corrosion kinetic. High speed dry face milling of biodegradable Mg-Ca alloy is initiated in this study as a possible way to achieve that goal. Polycrystalline diamond inserts are used to avoid material adhesion and likely fire hazards in machining Mg-Ca alloys. All the cutting tests are performed without using coolant to keep the manufacturing process ecological. High cutting speeds of up to 2800 m/min and a broad range of feed and depth-of-cut values are selected to cover finish and rough cutting regimes. The effect of different cutting parameters on surface integrity characteristics including surface topography, surface roughness, microstructure, microhardness, and residual stress are comprehensively investigated. 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 all highly compressive which is beneficial to corrosion implant to human body fluid.

Keywords: Biodegradable implant, surface integrity, magnesium-calcium alloy, high speed dry machining