Sintering of biocompatible P/M Co–Cr–Mo alloy (F-75) for fabrication of porosity-graded composite structures

Manufacturing of complex-shaped bimetals utilizing two-color powder injection molding (2C-PIM) and three-dimensional printing (3DP) processes, which basically involve sintering of a powder/binder mixture, has been attracted a great interest. This article addresses sintering of biocompatible Co–Cr–Mo alloy for manufacturing stepwise porosity-graded composite structures. Such composite structures provide strength at the core and a porous layer for the tissue growth. To evaluate the process, two grades of gas atomized Co–Cr–Mo powder with an average particle size of 19 and 63 μm were used. Isothermal and non-isothermal sintering behavior of the loose powders under hydrogen and argon atmospheres, which is a simulated condition of 2C-PIM and 3DP processes after de-binding, was studied. Microstructural characteristics of the sintered specimens were evaluated. It was found that an intermediate sintering temperature of 1280 °C in argon can be used for manufacturing of the porosity-graded composite layers, i.e., a relatively dense core (5% porosity) with a porous layer (33% porosity) can be produced. A hip-joint with a core/shell structure was produced as a case study.