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普遍使用的AISI 316L,奥氏体不锈钢由于具有优良的耐腐蚀性和生物兼容性广泛用于制药和食品工业。但是,对于接触表面相对滑移运动(经常具有自相配接触)的应用,比如泵、阀和轴承,AISI 316L的摩擦性能由于耐粘着磨损性低(会咬住)而不能满足要求。经常使用润滑油和涂层来减少磨损,但是润滑油在食品和制药加工设备上因卫生要求不能使用,所以需要表面改性来达到满意的摩擦性能。虽然奥氏体不锈钢冷加工后能很好硬化,但是不能通过热处理或传统的化学热处理,如渗碳来硬化,因为碳化铬沉积在晶界上会损害耐腐蚀性。不过低温渗碳(LTC)是一种有效的化学热处理,在大部分环境下能不降低奥氏体不锈钢耐腐蚀性提高耐磨性。事实上,LTC会在被处理钢表面生成20~30 mm厚的过饱和碳的扩散层,大大增加硬度(达到约1100 HV)而又没有碳化铬沉积。但是LTC处理不能减少钢对钢接触的摩擦系数,在许多LTC处理件的摩擦应用中出现这种情况。所以本项研究中,在LTC处理过的AISI 316L的外表面用PA-CVD在含氢碳气氛(a-C:H)中沉积薄涂层,从而达到既能降低磨损,又能降低自相配接触的摩擦系数。类金刚石碳(DL)或更特殊的a-C:H涂层(根据由VD12840)指南提出的分类)低摩擦和高耐磨性组合:也就是说,类金刚石碳受控于sp2到sp3碳的比例(特别是类金刚石的性质,如硬度和刚性是sp3位置强结合的结果),以及存在额外元素,如氢、硅或其他金属杂质。当用于如AISI 316L软基体,DLC涂层的摩擦性能提高可起到改善基体硬度的作用。这看作是典型的薄硬涂层,这利益于表面处理或过渡层增加基体的承载能力。在本项研究中,由LTC得到的扩散层用作支撑DLC顶层的负荷。但是L TC也增加基体的粗糙度,因为在奥氏体晶粒内形成滑移带,因此奥氏体膨胀。但是在DTC沉积前要求基体有低的表面粗糙度。所以要注意认别提高摩擦性能的最好处理程序,也就是a-C:H沉积前的抛光(在L TC后要求降低粗糙度)的影响。此外,评估L TC层对双重系统载荷能力的影响,可用比较a-C:H沉积在L TC处理过的钢上和直接在未处理的AISI 316L钢上的摩擦性能。最后,用未处理的和L TC处理的AISI 316L作为配对表面,在相反的材料上也研究了L TC处理的摩擦性能的影响。
The widely used AISI 316L, austenitic stainless steel is widely used in the pharmaceutical and food industries due to its excellent corrosion resistance and biocompatibility. However, AISI 316L, for applications such as pumps, valves and bearings, that have relatively slippery contact surfaces (often with self-mating contact), can not meet the requirements due to their low adhesion (biting) resistance to galling. Lubricants and coatings are often used to reduce wear, but lubricants can not be used on food and pharmaceutical processing equipment because of hygienic requirements and therefore require surface modification to achieve satisfactory friction performance. Although austenitic stainless steels are well hardened after cold working, they can not be hardened by heat treatment or conventional chemical heat treatment, such as carburization, since chromium carbide deposits on the grain boundaries impair corrosion resistance. However, low-temperature carburization (LTC) is an effective chemical heat treatment, in most cases can not reduce the corrosion resistance of austenitic stainless steel to improve wear resistance. In fact, LTC creates a 20-30 mm thick supersaturated carbon diffusion layer on the treated steel surface, significantly increasing hardness (up to about 1100 HV) without chromium carbide deposition. However, the LTC treatment does not reduce the coefficient of friction of steel on steel contact, as is the case with many LTC-treated friction applications. In this study, therefore, a thin coating was deposited on the outer surface of LTC-treated AISI 316L by PA-CVD in a hydrogen-containing carbon atmosphere (aC: H) to achieve both reduced wear and reduced self-mating contact Friction coefficient. Low-friction and high-wear combination: diamond-like carbon (DL) or more specific aC: H coating (according to VD12840) guidelines: That is, diamond-like carbon is controlled by the sp2 to sp3 carbon ratio (Especially diamond-like properties such as hardness and stiffness as a result of strong bonding at the sp3 position) as well as the presence of additional elements such as hydrogen, silicon or other metal impurities. The increased frictional performance of DLC coatings when used in soft substrates such as AISI 316L can serve to improve the substrate hardness. This is seen as a typical thin hard coating, which benefits from the surface treatment or transition layer to increase the load carrying capacity of the substrate. In this study, a diffusion layer from LTC was used as a load supporting the top of the DLC. However, L TC also increases the roughness of the matrix, because the slip band is formed in the austenite grains, so austenite expands. However, the substrate is required to have low surface roughness before DTC deposition. Therefore, attention should be paid to identify the best treatment procedure to improve the friction performance, that is, the impact of a-C: H pre-polishing (requiring roughness reduction after L TC). In addition, to assess the effect of L TC layer on the loading capacity of the dual system, we can compare the tribological properties of a-C: H deposited on LTC-treated steel and directly on untreated AISI 316L steel. Finally, the effect of the frictional properties of the L TC treatment was also investigated on the opposite material with untreated and L TC-treated AISI 316L as the mating surface.