MoO3-ZnO/镍基复合涂层制备及其摩擦学性能研究

利用等离子喷涂工艺制备了含氧化物(MoO₃-ZnO)的镍基复合涂层，通过UMT-3球盘式高温摩擦试验机评价了复合涂层在室温、400和800 ℃下的摩擦学性能，并采用扫描电镜(SEM)、能谱分析仪(EDS)、X射线衍射仪(XRD)以及拉曼光谱仪(Raman)等分析手段研究了涂层微观组织、物相组成以及磨损机理. 结果表明:在室温和400 ℃，复合涂层的摩擦系数和磨损率均高于Ni-5%Al金属基底，且随着氧化物含量的增加，润滑和耐磨性能均被削弱，主要表现为磨粒磨损和黏着磨损. 在800 ℃，MoO₃和ZnO的添加可以有效改善复合涂层的摩擦性能，随着其含量的增加，摩擦系数变化不明显，而磨损率逐渐增加. 特别是添加5%MoO₃和5%ZnO的复合涂层在800 ℃摩擦系数低至0.28，磨损率低至4.22×10?5 mm3/(N·m)，其良好的高温润滑耐磨性能得益于摩擦表面二元氧化物(NiO、MoO₃和ZnO)和三元氧化物(ZnMoO₄和NiMoO₄)的协同作用. 

Tribological Properties of Nickel-based Composite Coatings with the Addition of MoO3-ZnO

Nickel-based composite coatings with the addition of oxides (MoO₃-ZnO) were prepared by atmospheric plasma spraying. The wear tests were carried out on an UMT-3 ball-on-disc high temperature tribometer at room temperature, 400, and 800 ℃, respectively. And the microstructures, phase compositions, and wear mechanisms were analyzed by SEM, EDS, XRD, and Raman. The tribological mechanisms on the view of oxidation and tribo-chemistry were determined by the microstructure and phase composition analysis of the worn surface of both composite coatings and corresponding counterpart balls. The XRD patterns of composite coatings showed the presence of α-ZnMoO₄ within composite coatings, indicating the solid reaction between MoO₃ and ZnO during the plasma spraying process. The XRD peaks of α-ZnMoO₄ in composite coatings were more intensive with the increasing content of MoO₃ and ZnO powders in feedstock powders. And the structure of MoO₃ and ZnO powders remained stable during the spraying process. The cross-sectional microstructure of composite coatings exhibited a lamellar structure with several pores and un-melted particles. The content of Mo and Zn element in the composite coatings increased with the increasing content of MoO₃ and ZnO powders in feedstock powders. The friction coefficients and wear rates of the composite coating were higher than that of the Ni–5%Al(mass fraction) metal matrix at room temperature and 400 ℃. Moreover, the lubrication and wear resistance of the composite coatings deteriorated with the increase of oxides content, the wear mechanism was mainly manifested as abrasive wear and adhesive wear. The high coefficient of friction at room temperature was related to the lack of effective lubricants in the coatings, whereas the added oxides were lubricious at high temperatures. The high wear rates of composite coatings at 400 ℃ was mainly due to the softening effect of materials and the wear before the formation of a stable oxide layer. At 800 ℃, the tribological properties can be effectively improved by the addition of MoO₃ and ZnO. In particular, the composite coating with the addition of 5% MoO₃ and 5% ZnO exhibited the lowest friction coefficient (0.28) and the wear rate 4.22×10?5 mm3/(N·m)]. And the wear rates of composite coatings increased with the increasing content of MoO₃ and ZnO powders in feedstock powders, which was related to the increasing peeling areas on the worn surface of the composite coatings. A protective tribo-layer was observed on both coatings and counterpart Al₂O₃ balls at 800 ℃. Furthermore, the elements of composite coatings (Mo and Zn) transferred to the worn surface of corresponding counterpart balls and were compacted to a relatively smooth film, which prevented the direct contact between the coatings and the Al₂O₃ ball, thus providing a low shearing interface and reduce the friction. The excellent high temperature tribological performance can be attributed to the synergistic effect of binary oxides (NiO, MoO₃, ZnO) and ternary oxides (ZnMoO₄ and NiMoO₄) on the worn surfaces of both composite coatings and counterpart Al₂O₃ balls.