TiN涂层中表面裂纹产生的机理研究
Study on Mechanism of Surface Cracks in TiN Coating

为了揭示滑动摩擦接触条件下的TiN涂层表面裂纹的形成机理，对TiN涂层进行了划痕试验和有限元模拟。划痕试验结果表明在划痕表面产生了平均间距约为5.12 μm的弧型裂纹。采用三维有限元方法对划痕过程进行了模拟，模拟结果表明了涂层结构中的应力分布的特点。采用二维扩展有限元方法（XFEM）对划痕过程中的涂层的裂纹产生进行了模拟，模拟结果表明涂层中表面及界面裂纹主要是由最大拉应力引起的第一型裂纹；涂层亚表面裂纹是一种由拉应力和剪应力引起的复合型裂纹。表面裂纹的形成有三种方式：第一种方式是首先在涂层界面产生微裂纹，随着裂纹沿着厚度方向扩展到表面形成表面裂纹；第二种方式是在涂层表面直接形成表面裂纹；第三种方式是微裂纹首先在涂层亚表面形成，然后沿着厚度方向扩展到表面形成表面裂纹。模拟中发现在表面和界面首先产生微裂纹的数量比亚表面产生微裂纹的数量更多。随着裂纹的扩展和融合将导致涂层的剥落。
Both scratch test on TiN coating and finite element simulation are carried out in order to reveal the mechanism of surface crack of coating under frictionally sliding contact. The results of the scratch test show that arc-shaped cracks that have an average spacing of 5.12 μm come into being on the scratching surface. The three-dimensional finite element method is adopted to simulate the scratch process and the result indicates stress distributions in coating. Meanwhile the extended finite element method (XFEM) is applied to simulating cracks formation in the scratching process and the results show that surface cracks and interface cracks in coating results from the maximum tensile stress and those are mainly modelⅠcracks. Sub-surface cracks in coating are complex ones induced by both tensile stress and shear stress. Surface cracks are formed in following three ways. The first one is that microcracks at first emerge from the coating interface, and then surface cracks are formed with their propagating along coating thickness' direction to the surface. The second is that surface cracks are directly formed in the coating surface. The last is that microcracks at first are formed in the sub-surface of the coating,and then surface cracks come into being as their propagating along coating thickness' direction to the surface. In the process of simulation, it is found that the surface and the interface generate much more microcracks than the sub-surface does. With the propagation and fusion of cracks, the coating will spall