Deshpande P, Minfray C, Dassenoy F, Le Mogne T, Jose D, Cobian M, Thiebaut B
University Lyon, Ecole Centrale de Lyon, Laboratory of Tribology and System Dynamics, ENISE, ENTPE, CNRS UMR 69134 Ecully France.
TOTAL Marketing Services, Centre de Recherche de Solaize BP22-69360 Cedex France.
RSC Adv. 2018 Apr 20;8(27):15056-15068. doi: 10.1039/c8ra00234g. eCollection 2018 Apr 18.
Recent engine design and emission trends have led to the commercial use of Atmospheric Plasma Spray (APS) coatings for cylinder liner applications like the TiO 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 (AlO and ZrO). 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 TiO APS coating compared to reference steel. To explain the low friction behavior, tribofilm compositions were investigated and it was observed that MoS is always formed in the case of TiO APS with no oxysulphide species. For the reference steel, MoO S species are mainly detected in the tribofilms. XPS analyses performed on TiO APS flats when the counterpart material was changed from steel balls to ceramic balls suggested the formation of MoS (Mo in +iv oxidation state) and Mo-C (Mo in +iv or +ii oxidation state) species with a negligible amount of MoO (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.
近期的发动机设计和排放趋势已促使大气等离子喷涂（APS）涂层在气缸套应用中得到商业应用，如TiO APS涂层。我们之前的工作表明，与用二烷基二硫代磷酸钼（MoDTC）润滑的钢相比，这种类型的涂层显示出更好的摩擦性能。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、赫兹接触压力以及配对材料从钢球变为陶瓷球（Al₂O₃和ZrO₂）的影响。在一台用含MoDTC的基础油润滑的往复式（球-平面）摩擦磨损试验机上进行了球-平面摩擦磨损试验。结果表明，在包括MoDTC浓度、测试温度和接触压力在内的所有测试条件下，与参考钢相比，TiO APS涂层的摩擦和磨损更低。为了解释低摩擦行为，对摩擦膜成分进行了研究，观察到在TiO APS的情况下总是形成MoS，没有氧硫化物物种。对于参考钢，在摩擦膜中主要检测到MoO₂S物种。当配对材料从钢球变为陶瓷球时，对TiO APS平面进行的X射线光电子能谱（XPS）分析表明形成了MoS（Mo处于+iv氧化态）和Mo-C（Mo处于+iv或+ii氧化态）物种，而MoO₃（Mo处于+vi氧化态）的量可以忽略不计。还表明，摩擦膜内大量源自MoDTC（Mo处于+v氧化态）的钼原子在摩擦接触中被还原。基于我们之前工作中假设的摩擦催化行为，提出并讨论了MoDTC的分解机制。
