No abstract

Sliding wear behavior of laser-nitrided and thermal oxidation-treated Ti-5Al-5Mo-5V-1Cr-1Fe (TC18) alloy fabricated by laser melting deposition (LMD) has been investigated to improve on wear resistance of laser melting deposited titanium alloy. The microstructure, wear morphology, hardness and wear rate were examined for the unmodified, laser-nitrided and thermal oxidationtreated LMD Ti-5Al-5Mo-5V-1Cr-1Fe alloy. As compared to a/b basket weave microstructure with fine lamellar a (hcp) observed on the unmodified LMD Ti-5Al-5Mo-5V-1Cr-1Fe alloy, Ti, Ti 2 N and TiN were formed on the LMD specimens after laser nitriding. After thermal oxidation, a surface layer composed of rutile TiO 2 was formed on the LMD specimens along with coarsening of a lath. The increase in hardness and wear resistance of the lasernitrided LMD Ti-5Al-5Mo-5V-1Cr-1Fe alloy is attributed to hard dendritic TiN formed on the specimens. The wear rate of the thermal oxidation-treated LMD specimens was \1 % of that of the unmodified LMD specimens when hardness of the former was twice as much as the latter. The superior sliding wear resistance of the thermal oxidationtreated LMD specimens is attributed to the presence of the lubricious rutile oxide layer and hardened diffusion zone.

Recently, laser melting deposition (LMD) undergoes rapid development since its fabricating advantages make it particularly suitable for the fabrication of titanium aerospace components. The dry sliding wear behavior of forged, uncoated and laser nitrided LMD TC18 titanium alloy sliding against the forged TA15 alloy were investigated. Then, reasons of their wear behavior were further studied. The specimens were tested on the M-200 tester, worn surface morphology and wear debris were carefully analyzed by means of SEM and EDS. The results show that in the case of forged and LMD TC18 titanium alloy sliding against TA15 alloy, wear mechanism are abrasive wear and adhesive wear. Because of the lubricious nature of TiO2 oxides produced during sliding which reduces the wear and consequently wear loss, the wear resistance of forged TC18 titanium alloy is superior to that of LMD TC18 titanium alloy. After using laser nitriding treatment on LMD TC18 alloy, the formation of a protective layer composed of dendritic TiN attributes to significant wear resistance improvement.