A new concept of hip joint stem and its fabrication using metastable TiNbSn alloy

Cold worked (Ti-35%Nb)-4%Sn alloy rods were locally heated to investigate the gradation of mechanical properties and develop an advanced Ti alloy stem for application as an artificial hip joint. Cold groove rolling was found to decrease Young's modulus, but subsequent cold swaging increased Young's modulus and tensile strength. Heating one edge of the cold worked rods resulted in the tensile strength and Young's modulus increasing significantly in the heated zone; the increase varied depending on the distance from the heated zone. The increase in tensile strength was attributed to the ω precipitation and the additional microstructure refinement by reverse transformation of α″ to β. We could successfully fabricate an advanced hip joint stem with a tensile strength of 1.3 GPa in the proximal portion and Young's modulus of 43 GPa in the distal portion.