Fabrication of a high-performance hip prosthetic stem using β Ti-33.6Nb-4Sn

This study used severe cold rolling followed by cold swaging of β Ti-33.6% Nb-4% Sn rods to form a characteristic fiber structure composed of stress-induced α″ martensite with <010> texture and a β phase with <101> texture, resulting in a material with a low Young's modulus of 40GPa. The material's tensile strength of 1270MPa and fatigue strength of 850MPa were attained by heat treatment at 673K for 5h through fine α precipitation in the fiber structure. A new method of fabricating a high-performance hip prosthetic stem was investigated based on the low Young's modulus and high strength obtained. After fabricating the stem by cold rolling, cold swaging, cold die-forging and machining, its neck region was given higher strength through local heat treatment, while the low Young's modulus remained almost unchanged in a distal portion of the stem. When a stem tip in the distal part was heat treated at 423K, reverse α″→β transformation occurred and the tangent modulus decreased to less than 30GPa, accompanied by stress-induced β→α″. It was concluded that the method presented herein provided a low Young's modulus of approximately 40GPa in the distal part and high fatigue strength of approximately 850MPa in the neck region of a high-performance hip prosthetic stem.