Diamond coatings are known to improve the wear resistance properties of substrate materials. This paper aims at analyzing damage behavior of brittle diamond coating deposited on two different ductile substrates, namely pure-Ti and Ti-6Al-4V alloy, subjected to uniaxial tensile loading. In-situ tensile tests were conducted on diamond/Ti and diamond/Ti-6Al-4V coated samples to identify the stress-strain response and the damage behavior of the coating. Surface imaging was performed using scanning electron microscope (SEM). The cross sections were made with the focused ion beam (FIB) gun installed in SEM to observe the coating failure modes. Energy dispersive x-ray and x-ray diffraction analyses were carried out to determine composition. The SEM analysis revealed micro-crystalline morphology of the coating and FIB cross-sections showed diamond coating top-layer, TiC interlayer and substrate at the bottom. The XRD and EDX findings confirmed the regions observed in FIB cross-section via chemical analysis. The in situ tensile tests revealed that the coating had undergone failure through crack initiation, fragmentation and delamination. The bucking of the coating under transverse compressive strain of the substrate was also observed. The Ti-6Al-4V alloy caused early cracking and delamination of the coating owing to its higher yield strength and higher rate of stress transfer to the coating. Two-dimensional finite element models were developed to simulate various damage modes, such as cracking, buckling and delamination. Extended finite element method and cohesive damage modeling were exploited to observe cracking and buckling, respectively. Numerical results revealed that the coating was more prone to failure when Ti-6Al-4V, a high yielding less ductile, substrate was used instead of a low yielding highly ductile Ti substrate. Moreover, buckling was found to be the major reason of delamination than bulk cracking. The coating is, therefore, likely to delaminate more severely under the compressive (buckling) than the tensile (bulk cracking) mode of deformation.

已知金刚石涂层可改善基材材料的耐磨性。本文旨在分析沉积在两种不同韧性基体（纯钛和 Ti-6Al-4V 合金）上的脆性金刚石涂层在单轴拉伸载荷下的损伤行为。原位对金刚石/Ti 和金刚石/Ti-6Al-4V 涂层样品进行拉伸试验，以确定涂层的应力-应变响应和损伤行为。使用扫描电子显微镜（SEM）进行表面成像。横截面是使用安装在 SEM 中的聚焦离子束 (FIB) 枪制作的，以观察涂层失效模式。进行能量色散X射线和X射线衍射分析以确定组成。SEM 分析显示涂层的微晶形态和 FIB 横截面显示金刚石涂层顶层、TiC 夹层和底部的基材。XRD 和 EDX 的发现证实了通过化学分析在 FIB 横截面中观察到的区域。在原位拉伸试验表明，涂层已通过裂纹萌生、破碎和分层而失效。还观察到涂层在基材的横向压缩应变下的屈曲。Ti-6Al-4V 合金由于其较高的屈服强度和较高的应力传递到涂层的速率而导致涂层的早期开裂和分层。开发了二维有限元模型来模拟各种损坏模式，例如开裂、屈曲和分层。利用扩展有限元方法和内聚损伤模型分别观察开裂和屈曲。数值结果表明，当使用 Ti-6Al-4V（一种高屈服强度较低的延展性基材）代替低屈服强度高延展性 Ti 基材时，涂层更容易失效。而且，发现屈曲是分层而不是块体开裂的主要原因。因此，与拉伸（整体开裂）变形模式相比，涂层在压缩（屈曲）模式下可能更严重地分层。