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 Youngʹs modulus of 40 GPa. The materialʹs tensile strength of 1270 MPa and fatigue strength of 850 MPa were attained by heat treatment at 673 K for 5 h 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 Youngʹs 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 Youngʹs modulus remained almost unchanged in a distal portion of the stem. When a stem tip in the distal part was heat treated at 423 K, reverse α″→β transformation occurred and the tangent modulus decreased to less than 30 GPa, accompanied by stress-induced β→α″. It was concluded that the method presented herein provided a low Youngʹs modulus of approximately 40 GPa in the distal part and high fatigue strength of approximately 850 MPa in the neck region of a high-performance hip prosthetic stem.