Microstructure and wear behavior of inductive nitriding layer in Ti–25Nb–3Zr–2Sn–3Mo alloys

Abstract In human implant materials, beta (β) titanium alloys have been extensively used because of their excellent biocompatibility and lower elasticity modulus; however, they have poor hardness and wear resistance. Herein, vacuum induction nitriding technology is used to strengthen the surface of a Ti–25Nb–3Zr–2Sn–3Mo (TLM) alloy. The nitriding layer microstructure is characterised using X-ray diffraction (XRD), scanning electron microscopy (SEM)–energy dispersive spectrometry (EDS) and optical microscopy (OM). The mechanical properties of nitriding layer are tested using cross-sectional hardness gradient and nano-indentation. Furthermore, the wear resistance and mechanism of nitriding layer are examined using a self-made reciprocating wear tester, a three-dimensional (3D) profilometer and SEM, respectively. The results demonstrate that an approximately 30-μm thick nitriding layer is formed on the TLM alloy surface after induction nitriding treatment. Interestingly, it forms a gradient structure that can improve the hardness and wear resistance of samples. Moreover, at a maximum test load of 10 N, the abrasion loss of the raw sample is 463 times that of the nitriding sample. Furthermore, the friction coefficient of the raw sample significantly exceeds that of the nitriding sample at three test loads. The wear mechanism between the friction pair Al2O3 ball and the raw sample is primarily a combination of abrasive and adhesive wear, whereas that of the nitriding sample is primarily abrasive wear. The results demonstrate that the nitriding layer significantly improves the wear performance of TLM alloys.