Spinodal Zr–Nb alloys with ultrahigh elastic admissible strain and low magnetic susceptibility for orthopedic applications

Metallic biomaterials, such as stainless steels, cobalt–chromium–molybdenum (Co–Cr–Mo) alloys, and titanium (Ti) alloys, have long been used as load-bearing implant materials due to their metallic mechanical strength, corrosion resistance, and biocompatibility. However, their magnetic susceptibility and elastic modulus of more than 100 GPa significantly restrict their therapeutic applicability. In this study, spinodal Zr60Nb40, Zr50Nb50, and Zr40Nb60 (at.%) alloys were selected from the miscibility gap based on the Zr–Nb binary phase diagram and prepared by casting, cold rolling, and aging. Their microstructure, mechanical properties, corrosion resistance, magnetic susceptibility, and biocompatibility were systematically evaluated. Spinodal decomposition to alternating nanoscale Zr-rich β1 and Nb-rich β2 phases occurred in the cold-rolled Zr–Nb alloys during aging treatment at 650°C. In addition, a minor amount of α phase was precipitated in Zr60Nb40 due to the thermodynamic instability of the Zr-rich β1 phase. Spinodal decomposition significantly improved the mechanical strength of the alloys due to nanosized dual-cubic reinforcement. The Zr–Nb alloys showed an electrochemical corrosion rate of 94-262 nm per year in Hanks' solution because of formation of dense passive films composed of ZrO2 and Nb2O5 during the polarization process. The magnetic susceptibilities of the Zr–Nb alloys were significantly lower than those of commercial Co–Cr–Mo and Ti alloys. The cell viability of the Zr–Nb alloys was more than 98% toward MC3T3-E1 cells. Overall, the spinodal Zr–Nb alloys have enormous potential as bone-implant materials due to their outstanding overall mechanical properties, extraordinary corrosion resistance, low magnetic susceptibility, and sufficient bicompatibility. This work reports on spinodal Zr–Nb alloys with heterostructure. Spinodal decomposition significantly improved their mechanical strength due to the nanosized dual-cubic reinforcement. The Zr–Nb alloys showed large corrosion resistance in Hanks' solution because of formation of dense passivation films composed of ZrO2 and Nb2O5 during the polarization process. The magnetic susceptibilities of the Zr–Nb alloys were significantly lower than those of commercial Co–Cr–Mo and Ti alloys. The cell viability of the Zr–Nb alloys was more than 98% toward MC3T3-E1 cells. The results demonstrate that spinodal Zr–Nb alloys have enormous potential as bone-implant materials due to their outstanding overall mechanical properties, high corrosion resistance, low magnetic susceptibility, and sufficient biocompatibility.