Mechanical Performance of Artificial Hip Stems Manufactured by Hot Forging and Selective Laser Melting Using Biocompatible Ti-15Zr-4Nb Alloy

Yoshimitsu Okazaki; Jun Mori

doi:10.3390/ma14040732

Mechanical Performance of Artificial Hip Stems Manufactured by Hot Forging and Selective Laser Melting Using Biocompatible Ti-15Zr-4Nb Alloy

Materials (Basel). 2021 Feb 4;14(4):732. doi: 10.3390/ma14040732.

Authors

Yoshimitsu Okazaki¹, Jun Mori²

Affiliations

¹ Department of Life Science and Biotechnology, National Institute of Advanced Industrial Science and Technology, 1-1 Higashi 1-Chome, Tsukuba, Ibaraki 305-8566, Japan.
² Instron Japan Company Limited, 1-8-9 Miyamaedaira, Miyamae-ku, Kawasaki-shi, Kanagawa 216-0006, Japan.

Abstract

We investigated the microstructures, tensile properties, fatigue strengths, and durability limits of hot-forged Ti-15Zr-4Nb (Ti-15-4) alloy artificial hip stems. These properties were compared with those of Ti-15Zr-4Nb-4Ta (Ti-15-4-4) and Ti-6Al-4V (Ti-6-4) alloy stems annealed after selective laser melting. The tensile and fatigue properties of test specimens cut from Ti-15-4 stems annealed after hot forging were excellent compared with those of the Alloclassic Zweymüller Stepless (SL) stem, which is used globally. The 0.2% proof stress (σ₀._2%PS), ultimate tensile strength (σ_UTS), total elongation (TE) at breaking, and fatigue strength (σ_FS) after 10⁷ cycles were 919 ± 10, 983 ± 9 MPa, 21 ± 1%, and 855 ± 14 MPa, respectively. The durability limit (P_D) after 5 × 10⁶ cycles of Ti-15-4 stems was excellent compared with that of the SL stem. The σ_UTS values of 90°- and 0°-direction-built Ti-15-4-4 rods were 1032 ± 1 and 1022 ± 2 MPa, and their TE values were 14 ± 1% and 16 ± 1%, respectively. The σ_FS values of annealed 90°-direction-built Ti-15-4-4 and Ti-6-4 rods were 640 ± 11 and 680 ± 37 MPa, respectively, which were close to that of the wrought Ti-15-4 rod (785 ± 17 MPa). These findings indicate that the hot forging and selective laser melting (SLM) techniques can also be applied to the manufacture of artificial hip prostheses. In particular, it was clarified that selective laser melting using Ti-15-4-4 and Ti-6-4 powders is useful for the low-cost manufacturing of custom-made artificial joint prostheses and other prosthetic implants.

Keywords: artificial hip joints; biocompatible titanium alloy; custom-made implant; durability; fatigue property; hot forging; microstructure; selective laser melting; tensile property.