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

摘要

Novel biodegradable magnesium-calcium (Mg-Ca) implants have the ability to gradually dissolve and become absorbed in human body after implantation. The critical issue that hinders the application of Mg-Ca implants is their 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 face milling of biodegradable Mg-Ca alloy is used 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 alloy. All the cutting tests were performed without using coolant to keep the manufacturing process ecologic. High cutting speeds of up to 2800 m/min and a broad range of feed and depth-of-cut values were 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 were investigated. Average roughness value of 0.4 urn and shallow strain hardened depths were achieved. Little change of grain size could be observed in the near surface even for very slow feed value of 0.05 mm/rev. High compressive residual stresses were measured on the surface which is expected to be beneficial for corrosion resistance of implants in human body fluid.