固体润滑涂层的损伤裂纹演变及其摩擦学特性研究

发布时间：2018-07-31 13:49

【摘要】：先进表面工程技术作为现代工业发展的关键技术之一,已成为先进制造技术的前沿技术和赶超国际先进水平的重要前沿阵地。表面工程的发展极大的促进了固体润滑涂层的进步,在摩擦副表面生成具有优良减摩和耐磨性能的固体润滑涂层,配对成新的接触副,实现延长摩擦副使用寿命、提高机械效率以及节约材料的目的。目前,固体润滑涂层已在现代工业技术领域,如发动机和机械传动等,获得了广泛的应用并取得了巨大的经济价值和社会效应。受涂层和基体材料结构不匹配以及制备工艺影响而产生的较大薄膜涂层残余应力可能是涂层裂纹和界面分层损伤的催化剂,该问题的理论研究亟待加强,这对固体润滑涂层的制备具有重要的指导意义。而且,表征评定涂层-基体界面分层以及涂层自身裂纹问题已经成为固体润滑涂层耐用性和可靠性设计的障碍,迫切需要开展涂层失效的基础理论研究,并对涂层的失效预测和评价具有显著的意义。此外,研究固体润滑涂层润滑状态下的摩擦学特性,并从理论上通过合理的涂层参数和润滑设计,避免涂层-基体系统失效的产生,有效地提高摩擦副承载能力和使用寿命,对于开拓涂层摩擦学应用具有重要的理论意义和实际应用价值。本文针对上述固体润滑涂层-基体系统的界面分层损伤和涂层裂纹演变及其摩擦学特性的科学问题,以物理气相沉积涂层和钢基体系统为研究对象,系统性的开展了研究工作,其主要工作和成果总结如下:(1)针对涂层在残余应力下可能会出现的界面分层和涂层裂纹的问题,建立了考虑粗糙度的涂层-基体系统残余应力模型,通过扩展有限元技术、J积分法以及内聚力法相结合的手段从理论上研究了涂层在残余应力下界面分层损伤以及涂层裂纹的演变。表明粗糙面对涂层残余应力以及基体塑性行为均有较大影响;相比于界面法向应力,分层失效对界面切应力变化更为敏感;而多裂纹时的两近置的裂纹尖端更容易扩展并最终融合;并且,从力学角度证明沉积一层热膨胀系数适中的中间层可以更好的保护整个系统。(2)围绕涂层-基体界面分层以及涂层自身裂纹的如何评价的问题,通过纳米压痕方法对系统失效情况进行表征,建立了包含内聚力单元的涂层-基体系统压痕的有限元模型,考察了内聚力属性、涂层弹性模量以及厚度对涂层裂纹和界面分层的影响,同时揭示了涂层裂纹和界面分层两者的相互影响规律。表明增加涂层的内聚力/能虽可有效地防止其裂纹的产生,但同时也增大了界面分层失效的可能性;当界面内聚力处于某临界值时,界面耐分层能力最小;然而,涂层裂纹对于界面的内聚力属性变化并不敏感;而弹性模量越小的涂层系统越易免受这些伤害;涂层厚度在影响其裂纹和界面分层临界载荷方面也存在某一临界值。(3)利用复合离子镀膜技术在渗碳钢基体表面沉积类金刚石(DLC)涂层。使用纳米压痕法对其进行了实验研究,实时获得压头的载荷-位移曲线。曲线中存在若干跳跃点,意味着系统内部裂纹或界面分层失效的产生。压痕实验完成后,通过扫描电子显微镜和聚焦离子束系统观察发现,DLC涂层压痕处出现了规则的贯穿厚度的环形裂纹以及界面分层现象,实验结果验证了模拟仿真结果的正确性。最后,通过压痕结果估算了涂层断裂韧度和界面结合能。(4)建立了涂层-基体系统微观弹流润滑模型,基于Full-system有限元法,研究了涂层的弹流摩擦特性,评价了涂层厚度、涂层弹性模量、工况条件、界面微波谷、表面和界面粗糙度以及多层涂层对系统应力响应的影响,预测了重载下系统可能失效的位置。表明涂层厚度、弹性模量和工况变化会对其弹流特性产生重大的影响;同硬涂层相比,软涂层的弹流响应对速度和载荷的变化更为敏感;用力学的方式解释微裂纹一般萌生于界面微波谷处;且油膜压力以及界面剪应力在较软和较厚涂层上受表面粗糙度影响更小;同时粗糙界面的剪应力很大程度取决于涂层和基体的匹配度;而功能梯度多层涂层系统可有效预防界面分层以及亚表面点蚀失效。(5)通过四球实验对比研究了TiN、WC/C和DLC三种固体润滑涂层的摩擦磨损性能,揭示了它们重载润滑状态下的摩擦学机理。发现跑合稳定后的TiN涂层的摩擦系数最大,而DLC的最小;TiN涂层磨损失效方式为氧化剥落、WC/C为氧化点蚀,而DLC会在磨痕附近形成转移膜;则WC/C和DLC涂层表现出较好的减摩耐磨以及跑合特性。
[Abstract]:As one of the key technologies of modern industrial development, advanced surface engineering technology has become an important frontier for advanced manufacturing technology and overtaking international advanced level. The development of surface engineering has greatly promoted the progress of solid lubrication coating, and made solid lubricant with excellent friction reduction and wear resistance on the surface of the friction pair. The slippery coating, paired as a new contact pair, can prolong the service life of the friction pair, improve the mechanical efficiency and save the material. At present, the solid lubrication coating has been widely used in modern industrial technology, such as engine and mechanical transmission, and has achieved great economic value and social effect. The residual stress of large film coating produced by structural mismatch and preparation process may be a catalyst for coating cracks and interfacial delamination damage. The theoretical study of this problem needs to be strengthened. It has important guiding significance for the preparation of solid lubricating coatings. The grain problem has become an obstacle to the durability and reliability design of the solid lubricating coating. It is urgent to carry out the basic theoretical research on the failure of the coating, and have significant significance to the failure prediction and evaluation of the coating. In addition, the tribological characteristics of the solid lubrication coating are studied and the reasonable coating parameters and moistening are used in theory. The slip design avoids the failure of the coating matrix system and effectively improves the bearing capacity and service life of the friction pair. It is of great theoretical and practical value for the development of the coating tribological application. In this paper, the interfacial delamination damage, the evolution of the coating crack and the tribological characteristics of the above solid lubricating coating matrix system are discussed in this paper. The research work of physical vapor deposition coating and steel matrix system is carried out systematically. The main work and results are summarized as follows: (1) the residual stress modes of the coating matrix system considering the roughness of the coating are established to solve the problem that the coating may appear in the interfacial layer and the coating crack under the residual stress. By extending the finite element technique, the J integral method and the cohesive force method, the interfacial stratification damage and the evolution of the coating crack under the residual stress are theoretically studied. It shows that the roughness has a great influence on the residual stress and the matrix plastic behavior of the coating, and the interfacial failure is compared with the interface normal stress. The shear stress change is more sensitive, and the two near crack tip in the multi crack is easier to expand and eventually fuse; and, from the mechanical point of view, the medium layer with moderate thermal expansion coefficient can better protect the whole system. (2) the problem of how to evaluate the coating's self crack and how to evaluate the coating's own crack by the layer of the coating matrix interface. The nano indentation method was used to characterize the failure of the system. The finite element model of the indentation of the coating matrix system containing the cohesive unit was established. The influence of cohesive properties, the elastic modulus and the thickness of the coating on the coating cracks and the interfacial stratification were investigated, and the interaction law of the coating cracks and the interfacial stratification was revealed. The increasing cohesion and energy of the coating can effectively prevent the formation of the crack, but it also increases the possibility of the interfacial delamination failure. When the cohesive force is at a critical value, the interfacial lamination resistance is minimal. However, the coating cracks are not sensitive to the cohesive force properties of the interface, and the less the modulus of the coating, the more the coating system is. It is easy to avoid these injuries; the thickness of the coating also has a certain critical value in influencing the crack and the critical load of the interface layer. (3) the diamond like (DLC) coating is deposited on the surface of the carburized steel substrate by the composite ion plating technology. The experimental study is carried out by the nano indentation method. The load displacement curve of the pressure head is obtained in real time. At several jumping points, it means the failure of the internal crack or interface layer in the system. After the completion of the indentation experiment, it is found through the scanning electron microscope and the focused ion beam system that the circular crack of the regular penetrating thickness and the interfacial stratification appear at the indentation of the DLC coating. The experimental results verify the correctness of the simulation results. Finally, the fracture toughness and interfacial bonding energy of the coating are estimated by the indentation results. (4) the micro elastohydrodynamic lubrication model of the coating matrix system is established. Based on the Full-system finite element method, the Elastohydrodynamic friction characteristics of the coating are studied. The thickness of the coating, the elastic modulus of the coating, the working condition, the interface microwave Valley, the surface and the interfacial roughness are evaluated. The influence of multilayer coating on the stress response of the system is predicted. It is shown that the position of the system may fail under heavy load. It shows that the thickness of the coating, the modulus of elasticity and the change of the working condition have a great influence on its Elastohydrodynamic characteristics. Compared with the hard coating, the Elastohydrodynamic response of the soft coating is more sensitive to the change of velocity and load; the micro crack is explained by mechanical way. The effect of oil film pressure and interfacial shear stress on the surface roughness is smaller than that of the soft and thick coating, and the shear stress of the rough interface depends largely on the matching degree of the coating and the matrix, while the functionally graded multilayer coating system can effectively prevent the interfacial delamination and the subsurface pitting failure. (5) After four ball experiments, the friction and wear properties of three solid lubricating coatings of TiN, WC/C and DLC were compared and studied. The Tribological Mechanism of them under heavy load lubrication was revealed. It was found that the friction coefficient of the TiN coating was the largest and the DLC was the smallest after running in and out. The wear failure mode of TiN coating was oxidation peeling, WC/C as oxidation pitting, and DLC in the grinding mark. The transfer film was formed nearby, and the WC/C and DLC coatings showed good antifriction, wear resistance and running in characteristics.
【学位授予单位】：重庆大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TH117

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