Preparation of high-strength Co−Cr−Mo alloy rods via hot-caliber rolling

Co−Cr−Mo alloys have various remarkable properties, and their use has been extended in biomedical applications in recent times. In this study, small-diameter Co−Cr−Mo alloy rods, which can be used in spinal instrumentation surgery, were prepared using a developed manufacturing system that enables hot-caliber rolling immediately after the induction heating of a rod workpiece. The effects of rolling temperature (850−1150 °C) and the amount of deformation (up to 0.45 in equivalent strain) on the microstructure, mechanical properties, and cytocompatibility of the rods were examined to determine the processing−microstructure−property relationship and to optimize the processing parameters. The microstructural evolution, which was found to be associated with grain refinement due to the simultaneous dynamic recrystallization (DRX) and accumulation of lattice defects during hot-caliber rolling, significantly strengthened the alloy and maintained the ductility. Bi-directional deformation during hot-caliber rolling at higher rolling temperatures enhanced the DRX, thus realizing uniformly distributed fine grains without preferential orientations, which resulted in the homogeneous mechanical properties of the obtained rods. Consequently, an enhanced strength−ductility combination, which was superior to those obtained in the existing literature, was achieved. Moreover, the cytocompatibility experiments using human MG-63 osteoblast-like cells at various intervals (3, 6, and 10 days) revealed a limited detrimental influence on the cell proliferation and cell migration on the sample hot-rolled at 1150 °C. The developed manufacturing system can be employed for the fabrication of high-strength Co−Cr−Mo alloy rods with high durability, and it can be implemented in low-profile systems for spinal instrumentation surgery.