Synthesis of DLC Film on Titanium Alloy and Its Tribological Property Sliding against Different Mating Materials

Diamond-like carbon (DLC) film with high hardness and excellent tribological properties, could improve the tribological performance of titanium alloy. At present, the tribological behavior of DLC film deposited on titanium alloy surface by the plasma enhanced chemical vapor deposition (PECVD) method, sliding against a variety of different ceramic and metal materials in air is worth studying. The graded DLC film was deposited on surface of a TC4 titanium alloy by PECVD method. The microstructure, mechanical properties and the effect on the tribological properties for the as-prepared DLC films sliding against different mating ceramic balls and metal balls were investigated. The chemical composition and microstructure of the as-prepared DLC film were analyzed by Raman spectrum, scanning electron microscopy, energy dispersive spectrometer. The hardness and elastic modulus of the film were tested by nanoindentation. The bonding strength between the film and the substrate was measured by a scratch tester. The dry tribological performances of DLC film sliding against different ceramic and metal balls under air conditions were evaluated using a ball-on-disc wear tester. The results showed that the surface morphology of the graded DLC film was relatively smooth and uniform, and the film was well adhered to the substrate. The mechanical properties of deposited DLC film were excellent in this work. Eight tribo-pairs exhibited different friction and wear behaviors, and the ceramic/DLC pairs showed lower coefficient of friction and slighter wear of mating balls than the metal/DLC pairs, which were related to the properties of mating materials and action mechanism between the mating material and the DLC films. The possible friction and wear mechanisms of each tribo-pairs were further discussed. It suggested that for the ceramics/DLC tribo-pairs, it was easy to form stable carbonaceous transfer film on the ceramic balls due to high hardness and good wear resistance of the ceramic balls. SiC/DLC, Si₃N₄/DLC and ZrO₂/DLC exhibited mainly mild abrasive and adhesive wear while Al₂O₃/DLC revealed being damaged and peeled off but the friction coefficient was still at lower level because of the higher carbon content on the surface of the Al₂O₃ ball. And comparing the metals/DLC tribo-pairs with the ceramics/DLC tribo-pairs, it was difficult to maintain stable carbonaceous transfer film on the metal balls due to lower hardness of the metal balls, resulting in higher friction coefficient. Al/DLC exhibited mainly severe abrasive wear while brass/DLC, 304SS/DLC and GCr15/DLC revealed mild abrasive or adhesive wear. It also suggested that SiC/DLC, ZrO₂/DLC, 304SS /DLC and GCr15/DLC can be reasonable tribo-pairs because of relatively lower friction coefficients and wear rates of the DLC films and the small wear scars. Hertzian contact analysis showed that the variation trend of average friction coefficient and calculated contact radius was consistent in the ceramic/DLC tribo-pairs except ZrO₂/DLC, but this phenomenon was not found in metals /DLC tribo-pairs.