Effect of Element Diffusion on Structure and Tribological Properties of Cr2O3 Ceramic Films Prepared by Multi-arc Ion Plating

The Cr2O3 ceramic films prepared by multi-arc ion plating possess a low friction coefficient, good wear resistant and oxidation resistance. Meanwhile, high temperature annealing could improve the mechanical properties of Cr2O3 films significantly. In previous work, we found that the metal elements in the substrate would diffuse to the film surface and oxidize to form a ternary metal oxide with lubricating property. Thus, in order to research the diffusion behaviours of the metal elements in the substrate, the effects of microstructure evolution of the substrates on the metal elements diffusion in high temperature, and the evolutions of morphologies, microstructure and tribological properties of the Cr2O3 films were also researched in detail. Cr2O3 ceramic films were deposited on the surfaces of different substrate (Inconel 718 alloy, IC10 alloy, 45 steel and 316 stainless steel, polished to a roughness (Ra) of 20 to 40 nm) by multi-arc ion plating technology. Pure Ar (99.99%) and O2 (99.99%) were utilized as working gases. After cleaning with acetone for three times and drying with nitrogen, the substrates were pre-heated to 150 °C by placed into the vacuum chamber. Substrates were cleaned with Ar+ (bias voltage ‒800 V, pressure 2.1 Pa, 25 min) to remove oxides layer on the surface of the substrates. Firstly, Cr transition layer was deposited to improve adhesion strength between substrate and Cr2O3 film in pure Ar atmosphere, and then O2 was slowly introduced within 5 minutes, finally Cr2O3 film was deposited for 30 minutes. The working current, voltage, duty cycle, substrate temperature, working pressure and ratio of O2: Ar were 80 A, ‒100 V, 40%, 150 °C, 0.63 Pa, 110: 200 (mL/min), respectively. The films deposited on the surface of Inconel 718 alloy, IC10 alloy and 316 stainless steel were annealed at 1 000 °C, and the film deposited on the surface of 45 steel was annealed at 850 °C. Meanwhile, the corresponding different substrates were also annealed accordingly. Scanning electron microscope (SEM) and cold field emission scanning electron microscope (FESEM) are used to analyze the surface morphologies of the substrate and film before and after annealing and the changes of element content on the surface of the substrate and the film are analyzed by EDS. The phase of Cr2O3 films are analyzed by X-ray diffraction (XRD). The tribological properties of the substrate and film before and after annealing are analyzed by reciprocating friction and wear tester, a three-dimensional profiler and SEM. After annealing, the elements in the substrate diffuse to its surface, and the friction coefficient of Inconel 718 alloy, IC10 alloy and 45 steel are reduce. The metal elements in the substrate of Inconel 718 alloy and 316 stainless steel diffuse along the grain boundary of the Cr2O3 film to the surface in the process of annealing, and then form the ternary oxides in atmosphere. After annealing at 1 000 °C, the Ti element in Inconel 718 alloy diffuse to the surface of the Cr2O3 film and form a mesh-like heave structure which comprised of CrTiO3 and Cr2O3. The Mn element in 316 stainless steel diffuse to the surface of the Cr2O3 film and form spinel structure of MnCr2O4 phase. After annealing at 850 °C, the Cr2O3 film deposited on surface of 45 steel forms large particles dominated by Fe elemen. The phase of the film surface is a mixed phase of Fe2O3 and Cr2O3. Metal elements in the substrate are not found on the surface of the Cr2O3 film deposited on the IC10 alloy, and the main phase is Cr2O3. The friction coefficient of the Cr2O3 film reduces to about 0.45 after annealing. Metal elements in Inconel 718 alloy, 45 steel and 316 stainless steel diffuse to the surface of the film, which has a great influence on the phase composition, surface morphologies and tribological properties of the Cr2O3 film. The Cr2O3 film deposited on the surface of the IC10 alloy has a poor anti-wear performance after annealing. The Cr2O3 film deposited on the surface of Inconel 718 alloy exhibits excellent tribological properties. © 2022, Chongqing Wujiu Periodicals Press. All rights reserved.