Development of new Co-Cr-W-based biomedical alloys: Effects of microalloying and thermomechanical processing on microstructures and mechanical properties

摘要

The application of computer-aided design and computer-aided manufacturing (CAD/CAM) to dentistry has recently attracted considerable attention as a new technique for designing and fabricating custom-made dental implants. Here, a strategy combining microalloying with thermomechanical processing are described to design new Co-28Cr-9W-1Si-C (wt%) alloys for use as disks in the CAD/CAM-based machining of dental restorations. On the basis of our thermodynamic calculations, Si and C were selected as alloying elements that cause the brittle σ phase precipitates to be replaced with the plastically deformable Laves phase and thus enhance the alloy's hot workability. The effect of thermomechanical processing on the microstructure evolution and mechanical properties of the designed alloys was preliminarily studied by performing multipass hot rolling. The hot-rolled alloys exhibited refined grains (mean grain sizes ～10 μm) and high densities of lattice defects (dislocations, stacking faults, etc.), both of which were obtained as a result of dynamic recrystallization during hot rolling. It was found experimentally that this approach permits the alloy strength and ductility to be increased simultaneously. The static recrystallization occurring during cooling after deformation also modifies the mechanical properties of the alloys. Carbon doping (＜0.1 wt%) increases the amount of precipitates and further improves both the strength and elongation-to-failure of the hot-rolled alloys. Thus, the newly developed alloys have advantageous characteristics in terms of both fabrication and mechanical properties. In addition, the outstanding tensile ductility of the developed alloys could make them suitable for vascular stents.