Abstract In the aviation industry, water droplet erosion (WDE) takes place when an aircraft takes off on as wet runway or flies through rain or clouds. The leading edge of turbofan blades suffers from high-speed (300–400 m/s) impingements of water droplets, resulting in material removal that subsequently changes the leading edge profile and surface roughness. This affects the aerodynamic performance of turbofan blades, which eventually leads to efficiency drop of the aircraft engine and the need to replace and/or recondition the blades. A coating solution is targeted, such that, not only that it resists the high impact pressure but also inhibits stress wave reinforcements at the coating-substrate or interlayers interfaces. Past studies indicate similar damage mechanisms to WDE are generated by cavitation erosion (CE) during the early stages (incubation). Hence, CE is introduced in this study to predict the WDE performance. The coatings studied were nanostructured CVD tungsten/tungsten carbide coatings, either hierarchical or monotonic in design, on Ti6Al4V alloy grade 5 substrates. In-depth understanding on the coating damage mechanisms are established by correlating the coating performance with microstructure, crystallographic texture, interface design, coating deposition conditions and mechanical properties for the first time. A particular crystalline texture was found that gives optimum performance. The effect of the initial coating topography on the CE performance is effectively characterised by the surface parameters Ssk and Sku. The damage was found to initiate at the grain boundaries of the exposed surfaces. The hierarchical coating microstructure demonstrated enhancement in CE performance compared to a monotonic columnar grain structure. Additionally, it is found that the coating performance under dynamic compressive loadings could not be predicted by a simple H/E approaches. However, combining the H/E ratios with the factors of microstructure and crystal orientations might further facilitate the understanding of coating performances along with better understanding of the role of compressive residual stresses and stress waves propagation or reinforcement through coating depth and at the top surface of the coating.

中文翻译：

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CVD W/WC涂层的气蚀性能

摘要 在航空工业中，当飞机在潮湿的跑道上起飞或飞过雨或云时，就会发生水滴侵蚀（WDE）。涡轮风扇叶片的前缘受到水滴的高速 (300-400 m/s) 冲击，导致材料去除，随后改变前缘轮廓和表面粗糙度。这会影响涡轮风扇叶片的空气动力学性能，最终导致飞机发动机的效率下降以及需要更换和/或修复叶片。涂层溶液是有针对性的，这样，它不仅能抵抗高冲击压力，而且还能抑制涂层-基材或夹层界面处的应力波增强。过去的研究表明，早期（孵化）阶段的空蚀 (CE) 会产生与 WDE 类似的损坏机制。因此，本研究中引入了 CE 来预测 WDE 性能。所研究的涂层是 Ti6Al4V 合金 5 级基材上的纳米结构 CVD 钨/碳化钨涂层，在设计上可以是分层的或单调的。首次通过将涂层性能与微观结构、晶体结构、界面设计、涂层沉积条件和机械性能相关联，建立对涂层损伤机制的深入理解。发现了一种特殊的结晶结构，可提供最佳性能。表面参数 Ssk 和 Sku 有效表征了初始涂层形貌对 CE 性能的影响。发现损坏始于暴露表面的晶界。与单调柱状晶粒结构相比，分层涂层微观结构表现出增强的 CE 性能。此外，还发现动态压缩载荷下的涂层性能无法通过简单的 H/E 方法进行预测。然而，将 H/E 比与微观结构和晶体取向的因素相结合可能会进一步促进对涂层性能的理解，同时更好地了解压缩残余应力和应力波通过涂层深度和顶部表面传播或增强的作用。涂层。与单调柱状晶粒结构相比，分层涂层微观结构表现出增强的 CE 性能。此外，还发现动态压缩载荷下的涂层性能无法通过简单的 H/E 方法进行预测。然而，将 H/E 比与微观结构和晶体取向的因素相结合可能会进一步促进对涂层性能的理解，同时更好地了解压缩残余应力和应力波通过涂层深度和顶部表面传播或增强的作用。涂层。与单调柱状晶粒结构相比，分层涂层微观结构表现出增强的 CE 性能。此外，还发现动态压缩载荷下的涂层性能无法通过简单的 H/E 方法进行预测。然而，将 H/E 比与微观结构和晶体取向的因素相结合可能会进一步促进对涂层性能的理解，同时更好地了解压缩残余应力和应力波在涂层深度和顶部表面传播或增强的作用。涂层。