Study on the Evaluation of Coating Adhesion and Strength of Metal Coated with Ceramic Thin Film

用于各种机械部件的陶瓷涂层提高了耐磨性、耐热性、切削能力或耐腐蚀性。金属涂层技术将被广泛应用于各种功能性能要求高的机械零件和结构。本研究的目的是阐明涂层的附着力，薄膜的强度和涂层对金属疲劳性能的影响。采用物理气相沉积（PVD）和化学气相沉积（CVD）方法在0.37%碳钢表面镀TiN涂层，进行了划痕试验、静态拉伸试验、X射线法测量膜层残余应力、载荷控制高周疲劳试验和应变控制低周疲劳试验。本研究的主要结论如下：1. PVD镀TiN膜的划痕附着力高于CVD镀TiN膜。划痕试验中涂层失效模式各不相同; PVD ...更多信息 薄膜的弯曲导致薄膜的碎裂而失效，而CVD薄膜的弯曲导致薄膜的剥落.从静态拉伸试验中发现，PVD和CVD涂层膜上的裂纹分别在0.40%和0.87%的总拉伸应变下发生，并且它们随着应变而增加。结果表明，拉伸应变下涂层的划痕附着力和断裂没有任何共同特征.涂层试样的疲劳寿命受外加应力比和应变幅水平的影响。这是由于涂层膜的破裂引起的基材中的裂纹萌生行为。如果涂层在疲劳过程中由于涂层本身的疲劳破坏或基体金属塑性变形的累积而失效，涂层试样的疲劳寿命比未涂层试样的疲劳寿命降低。涂层膜中的缺陷在基材处引起许多裂纹。涂层试样的疲劳强度在低应变幅区和应力比为-1时有所提高，这是因为试样表面的硬质涂层起到了阻挡位错逸出的作用，延缓了裂纹的萌生.采用预裂纹涂层试样在空气和3.0%NaCl溶液中进行了旋转弯曲疲劳试验。与未涂层试件相比，预缺陷涂层试件的疲劳寿命显著降低。通过断口观察和疲劳小裂纹扩展规律的疲劳寿命估算，解释了在疲劳过程的早期，沿膜层缺陷沿着出现的多条裂纹相互连接并扩展成一条大裂纹。少

The ceramic coating for various kinds of machine components improves the wear resistance, heat resistance, cutting ability or corrosion resistance. Coating technology on metals will be utilized more widely for various kinds of machine components and structures which require high functional properties. The aim of this investigation is to clarify the coating adhesion, strength of thin film and the effect of hard thin film coated on the fatigue behavior of metals. Scratch test, static tensile test, residual stresses measurement in film by the X-ray method, and load-controlled high-cycle and strain controlled low-cycle fatigue tests were conducted, using specimen of 0.37% carbon steel coated with TiN by physical vapor diposition (PVD) and chemical vapor diposition (CVD) methods. Main conclusions obtained in this study are as follows:1. The scratch adhesion of TiN film coated by PVD is higher than that coated by CVD. Coating failure modes in the scratch test are different in each other; PVD … More film is failed by chipping as a result of the bending of film and CVD film is spalled by buckling.2. From the static tensile tests, it was found that flaws on PVD and CVD coating films occurred at the total tensile strains of 0.40% and 0.87%, respectively, and that they increased with the strain. It has been shown that scratch adhesion and fracture of coating film under tensile strain does not share any features.3. The fatigue life of specimens coated is affected by the applied stress ratio and the strain amplitude level. This is due to the crack initiation behavior in the substrate induced by the rupture of the coating film. The fatigue life of coated specimen decreased as compared with that of an uncoated one, if coating film fails during fatigue process as the results of fatigue damage of film itself or accumulation of plastic deformation of substrate metal. Many cracks were induced at the substrate by flaws in the coating film. The increase in fatigue strength of the coated specimen was observed under the region of low total strain amplitude and under the stress ratio of -1, because crack initiation was delayed by the hard coating film on the specimen surface which acted as a barrier to the egress of dislocations.4. The rotating bending fatigue tests were conducted in air and in 3.0% NaCl solution using the pre-flawed coating specimens. The fatigue life of pre-flawed coating specimen remarkably decreased as compared with that of an uncoated specimen. It was explained by the observation of fracture surface and the estimation of fatigue life based on the small fatigue crack propagation law that many cracks occured along the flaw of film are coalesced in each other and grow to large one crack at the early stage of fatigue process. Less