Abstract
Frictional wear resistance is one of the important properties of metallic biomaterials. Surface hardening treatments such as oxidizing, nitriding and ion implantation tend to be applied for improving the wear resistance of titanium and its alloys. The gas nitriding process is expected to further improve the wear resistance of newly developed β-type Ti-29Nb-13Ta-4.6Zr alloy (TNTZ). However, it is also possible to degrade the mechanical performance such as tensile and fatigue strength of TNTZ thorough their processes. Therefore, the gas nitriding process was carried out in this study to improve the wear resistance of TNTZ and an α+β type Ti-6Al-4V ELI alloy (Ti64), which is one of the titanium alloys applied for medical applications, in simulated body fluid (Ringer's solution). The change in their tensile and fatigue properties were also investigated in order to confirm the reliability as biomedical materials. The Vickers harnesses near the specimen surface of nitrided TNTZ and Ti64, where TiN and Ti_2N forms, increases significantly as compared to that of their matrices. The wear resistances of TNTZ and Ti64 are improved significantly in Ringer's solution by nitriding process as compared to those of as-solutionized TNTZ (TNTZ_<ST>) and Ti64. The tensile strength of nitrided TNTZ increases by around 90 MPa as compared to that of TNTZ_<ST>. The tensile strength of nitrided Ti64 does not change significantly at all nitriding temperatures. On the other hand, their elongation decrease with increasing the nitriding temperature. The runout (plain fatigue limit) of TNTZ subjected to a nitriding process at 1223 K was around 300 MPa, and was 75 MPa higher than that of Ti64 subjected to a nitriding process at 1223 K although the tensile strength of the nitrided TNTZ was 200 MPa smaller than that of the nitrided Ti64. The run out is a little smaller than that of TNTZ_<ST>.
