Tribological Performance of New Bearing Friction Pair of Babbitt Alloy and TC4 Titanium Alloy under Oil Lubrication and Dry Friction Conditions

To improve the output efficiency and reliability of steam turbines, a lightweight design of the steam turbine rotor was carried out. TC4 titanium alloy was selected as the lightweight material and compared with common rotor materials to explore its friction and wear characteristics. For the friction and wear characteristics of the new sliding bearing composed of titanium alloy rotor and babbitt metal bush, SnSb11Cu6 tin-based babbitt metal test blocks were used to form ring-block friction pairs with TC4 titanium alloy rings and 45 steel rings respectively. Performance tests under variable load and speed conditions were conducted on a ring-block friction and wear tester to explore the tribological performance of the two types of friction pairs under dry friction and oil lubrication conditions, and their friction and wear mechanisms were analyzed in combination with surface morphology and wear amount. The results showed that under oil lubrication conditions, the friction coefficient of the 45 steel friction pair increased with the increase of linear speed, showing a "bathtub curve", but the TC4 titanium alloy friction pair showed a "cone line", and the latter’s friction coefficient decreased more steeply. At a load of 50 N, the friction coefficient of the 45 steel friction pair was less than that of the TC4 titanium alloy friction pair; when the load was ≥100N, the friction coefficient of the TC4 titanium alloy friction pair was smaller. Under dry friction conditions, the friction coefficient of the 45 steel friction pair changed more drastically with the increase of load and linear speed, while the TC4 titanium alloy friction pair was more stable. When the load was ≤100 N, the friction coefficient of the TC4 titanium alloy friction pair was less than that of the 45 steel friction pair; when the load was ≥150 N, the friction coefficient of the 45 steel friction pair was smaller. Overall, under the same working conditions, the wear amount of the TC4 titanium alloy friction pair was larger than that of the 45 steel friction pair. Under oil lubrication, the volumetric wear rate of 45 steel was 72.57 mm³/(N·m), and that of TC4 titanium alloy was 994.90 mm³/(N·m), with the former being 13.7 times that of the latter. Under dry friction, the volumetric wear rate of 45 steel was 753.62 mm³/(N·m), and that of TC4 titanium alloy was 2 884.26 mm³/(N·m), with the former being 3.8 times that of the latter. Under oil lubrication conditions, the surface morphology of both 45 steel and TC4 titanium alloy friction pairs was good, with a relatively smooth surface, slight scratches and pits, and slight adhesive wear and abrasive wear. Under dry friction conditions, both 45 steel and TC4 titanium alloy friction pairs had obvious plough-like scratches and large flake spalling, with severe adhesive wear and abrasive wear, and the latter had more obvious surface damage. Therefore, it could be seen that when working under oil lubrication environment, the TC4 titanium alloy-babbitt metal new bearing could basically replace the 45 steel-babbitt metal bearing; when working under dry friction or low-speed heavy-load extreme conditions, surface treatment of TC4 titanium alloy was needed to improve the friction and wear performance of the friction pair.