Recent engine design and emission trends have led to the commercial use of Atmospheric Plasma Spray (APS) coatings for cylinder liner applications like the TiO₂ APS coating. It was shown in our previous work that this type of coating showed better friction results compared to steel lubricated with MoDTC. To further investigate this feature, a parametric study was carried out involving the effect of MoDTC concentration, test temperature, Hertzian contact pressure and the change of counterpart materials from steel balls to ceramic balls (Al₂O₃ and ZrO₂). Ball-on-flat tribotests were carried out on a reciprocating (ball-on-flat) tribometer lubricated with base oil containing MoDTC. Results show that for all the test conditions used including the concentration of MoDTC, test temperature and the contact pressure, lower friction and wear is observed for the TiO₂ APS coating compared to reference steel. To explain the low friction behavior, tribofilm compositions were investigated and it was observed that MoS₂ is always formed in the case of TiO₂ APS with no oxysulphide species. For the reference steel, MoO_xS_y species are mainly detected in the tribofilms. XPS analyses performed on TiO₂ APS flats when the counterpart material was changed from steel balls to ceramic balls suggested the formation of MoS₂ (Mo in +IV oxidation state) and Mo–C (Mo in +IV or +II oxidation state) species with a negligible amount of MoO₃ (Mo in +VI oxidation state). It was also shown that a significant amount of molybdenum atoms inside the tribofilm, originating from MoDTC (Mo in +V oxidation state) were reduced in the tribological contact. A mechanism for the decomposition of MoDTC on the basis of tribocatalytic behaviour hypothesized in our previous work was proposed and discussed.

中文翻译：

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摩擦改性剂 MoDTC 存在下 TiO2 大气等离子喷涂 (APS) 涂层的摩擦催化行为：参数研究

最近的发动机设计和排放趋势已导致将大气等离子喷涂 (APS) 涂层用于气缸套应用，例如 TiO ₂ APS 涂层。在我们之前的工作中表明，与使用 MoDTC 润滑的钢相比，这种类型的涂层表现出更好的摩擦结果。为了进一步研究这一特性，进行了一项参数研究，涉及 MoDTC 浓度、测试温度、赫兹接触压力以及从钢球到陶瓷球的对应材料（Al ₂ O ₃和 ZrO ₂）。在用含有 MoDTC 的基础油润滑的往复式（球对平）摩擦计上进行球对平面摩擦试验。结果表明，对于所有使用的测试条件，包括 MoDTC 的浓度、测试温度和接触压力，与参考钢相比， TiO _{2 APS 涂层的摩擦和磨损均较低。}为了解释低摩擦行为，研究了摩擦膜成分，观察到在没有氧硫化物物质的 TiO ₂ APS的情况下总是形成MoS _{2 。}对于参考钢，主要在摩擦膜中检测到MoO _x S _y物种。对 TiO _{2进行的 XPS 分析}当对应材料从钢球变为陶瓷球时，APS 平坦表明形成了 MoS ₂（Mo + IV氧化态）和 Mo-C（Mo + IV或 + II氧化态）物种，而 MoO 的量可忽略不计₃ (Mo in + VI氧化态)。还表明，摩擦膜内的大量钼原子源自 MoDTC（Mo+ V氧化态）在摩擦接触中被还原。提出并讨论了基于我们之前工作中假设的摩擦催化行为的 MoDTC 分解机制。