Research On Wear Behavior And Wear Mechanism Of Titanium Alloys

Titanium alloys are widely used because of their excellent performance, but their acknowledged poor sliding wear resistance severely precludes their applications. Meanwhile, the research on the sliding wear of titanium alloys themselves has been limited till now. The research community lacks comprehensive and deep understanding of the sliding wear behavior and wear mechanism for titanium alloys. Therefore, the research on dry sliding wear behavior and wear mechanism of titanium alloys is of important theoretical significance and practical application value. The wear behaviour and wear performance of TC4and TC11alloys were systematically studied under the different conditions and couterface materials in this study. The morphorlogies, compositions and structures of worn surfaces, cross-section subsurfaces, and wear debris were observed and measured thoroughly by using SEM, EDS, XRD, et al, and the wear mechanism of titanium alloys was explored. Tribo-layers and tribo-oxides of titanium alloys, as well as their effect on the wear behavior and their operation mechanism were focused on to be investigated.The results show that two typical titanium alloys shared the commonness of wear behaviour. At25℃-300℃, the wear rate increased with an increase of the load in most cases. At400℃, most of wear rates decreased, and slightly fluctuated as a function of load under50-250N; the wear rate substantially increased at250N in the few cases. At500℃-600℃, the wear rate decreased sharply and achieved very low values except for the titanium alloy/W6Mo5Cr4V2tribo-system at500℃and250N. The wear rate of TC11alloy was lower than that of TC4alloy at high temperature. More importantly, a severe-mild wear transition arised with an increase of the temperature in two typical titanium alloys, which was obviously different from the steel and other metal alloys. The titanium alloys possessed the poor wear performance below the critical conditions, but the excellent wear performance above the critical conditions. It was also found that the counterface material had significant influences on the wear rate of titanium alloys, but the effect on the wear mechanism was relatively small. At400℃-600℃, the wear rates of titanium alloys in the titanium alloy/W6Mo5Cr4V2tribo-system were higher than those in the titanium alloy/GCr15tribo-system.The wear mechanism of titanium alloys varied as a function of sliding conditions. At25℃-300℃, adhesive wear and abrasive wear were main mechanisms in most load conditions. At400℃, in most cases, adhesive wear, abrasive wear and oxidative mild wear co-existed. In few cases, adhesive wear, abrasive wear and plastic extrusion wear prevailed. At500℃-600℃, oxidative mild wear prevailed in most load conditions; adhesive wear, abrasive wear and plastic extrusion wear cooperated in few load conditions.It was noticed that tribo-layers always existed on the dry sliding surfaces of titanium alloys. But their composition and structure of tribo-layers varied with the sliding conditions, thus their functions were different. Whether the tribo-layers were protective or not, depends on their amount, compactness and the content of tribo-oxides. With the increase of temperature, tribo-layers and tribo-oxides increased, and the compact tribo-layers took a wear-reducing effect. For titanium alloys, tribo-layer can be divided into two categories:no-oxide tribo-layer and tribo-oxide layer. At lower temperature, tribo-layers with no oxide or trace oxides had no wear-reducing effect; at higher temperature, tribo-layers containing a small amount of tribo-oxides presented a certain degree of protecive effect; at further higher temperature, tribo-layers with a large amount of tribo-oxides showed full protection effect. The results showed that hard counterface material would result in the unstable existence of tribo-oxide layer. Thus, for titanium alloy/steel tribo-system, GCrl5was more suitable than W6Mo5Cr4V2for counterface material. It was suggested that titanium alloy and GCr15steel was an ideal high temperature tribo-pair.