Abstract
This study experimentally investigated the effect of surface textures on the tribological mechanism of nitrided titanium alloy (Ti–6Al–4V). The titanium alloy samples were nitrided at various temperatures ranging from 750 to 950 °C for 10 h in a plasma nitriding furnace. Then, surface textures were fabricated on the polished titanium alloy and plasma nitrided samples by laser process system. The surface roughness, microhardness, and constitution of samples treated by single nitriding and samples treated by composite technology were characterized. The tribological properties of the samples were investigated on a CSM ball-on-disc tribometer. The results show that plasma nitriding effectively enhances the wear resistance of the substrate. The wear rate decreases first and then increases with the increase of nitriding temperature, and the wear rate reaches the minimum at 900 °C. However, the increase in roughness caused by nitriding treatment leads to an increase in the friction coefficient. It is found that surface textures can obviously reduce the friction coefficient of the nitrided titanium alloy. In addition, it can also reduce the wear rate of titanium alloys after nitriding at 900 and 950 °C. It can be concluded that the nitriding and surface texturing combined treatment can obviously reduce the friction coefficient and wear rate at the nitriding temperatures of 900 and 950 °C. This is attributed to the combined effect of high hardness of nitride layers and the function of micro-trap for wear debris of surface textures.
Highlights
Titanium and titanium alloys possess good comprehensive properties, such as low density, high specific strength, high temperature resistance, corrosion resistance, magnetic resistance, impact resistance, and good biocompatibility, having extensive application prospects in the aviation field [1,2].the low hardness and poor tribological performance limit the applications of titanium alloys, such as the application of titanium alloy fasteners in aerospace [3,4]
Plasma nitriding (PN) technology, which has the advantages of controllable thickness and structure of the nitride layer, good process repeatability, and wide range of nitriding temperatures, is very suitable for the modification of titanium alloy [20]
The previous work shows that the nitrided titanium alloy has a higher hardness, which is of great benefit to improve the service life [33], but the brittleness of nitriding layers results in the abrasive wear
Summary
Titanium and titanium alloys possess good comprehensive properties, such as low density, high specific strength, high temperature resistance, corrosion resistance, magnetic resistance, impact resistance, and good biocompatibility, having extensive application prospects in the aviation field [1,2]. Materials 2019, 12, 301 nitriding and laser surface texturing are widely applied to improve the tribological performance of titanium [18,19]. Yamakiri et al [32] performed dimple patterns on the Si3 N4 by using a Q-switch YAG laser They found that the dimple textures have an important function of trapping wear debris and reducing abrasive damages on the sliding surface. The previous work shows that the nitrided titanium alloy has a higher hardness, which is of great benefit to improve the service life [33], but the brittleness of nitriding layers results in the abrasive wear. Borghi et al [34] studied tribological effects of surface texturing on nitriding steel for high-performance engine applications, and the results show that in “dry contact” configuration, for a normal load of 1N, friction coefficient is reduced to about 10% from untextured to textured surface. The present work aims to study the combined effect of surface textures and nitriding on the tribological performance of titanium alloy
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