W/B4C纳米多层涂层的界面结构和强韧化机理研究

Developing the strength-toughening hard coatings has become one of the hot research topics. And it is a research trend for future coatings to improve the performance through controlling the microstructure on the atomic scale. W/B4C multilayer coatings, due to the combination of B4C with excellent high temperature hardness and wear resistance and W with good chemical stability in the W-B-C ternary system, is of great potential as protective coatings of cutting tools. Therefore, a systematic study on the effect of interface performance on the mechanical properties and wear resistance will be carried out by both experimental and simulation methods in this project to reveal the strength and toughening mechanism of W/B4C multilayer coatings. The coatings will be prepared by target-substrate bi-pulse dc magnetron sputtering system, and then the complex nanocrystalline-amorphous interface behavior, such as composition, roughness, continuity, distributions of elements and atomic arrangement in the interfacial zone, will be investigated. First-principles method will be used to determine the most stable interface model and the formation mechanism of interface between W and B4C layers. The influence of interface on the mechanical properties and wear resistance of the coatings will also be studied. Furthermore, the strength and toughening mechanism of W/B4C multilayer coatings from the angle of interface performance will be explored in depth. This work, enriched the strength and toughening theory of multilayer coatings, will lay a theoretical foundation and technical support for the optimal interface and property design of nanocrystalline-amorphous multilayer coatings.

强韧化的硬质涂层已成为涂层领域的研究热点之一，在原子尺度上调控涂层微结构以改善涂层性能是未来涂层研究的发展趋势。W/B4C纳米多层涂层结合了硬质相B4C优异的高温硬度、耐磨性和韧性相W良好的化学稳定性，是一种极具潜力的涂层体系。因此，本项目提出采用实验为主模拟为辅的研究手段，系统研究W/B4C纳米多层涂层的界面结构对其力学性能和耐磨性能的影响机制，揭示并掌握该涂层的强韧化机理。首先采用靶材-基底双脉冲直流磁控溅射方法制备W/B4C涂层，分析测试该涂层中纳米晶-非晶界面的厚度、粗糙度和连续性，以及界面处元素分布、原子排列等特征，并通过第一性原理模拟方法确定最优界面结合方式和界面形成机理，深入分析界面微观结构与涂层宏观力学性能的内在联系，从界面结构角度揭示W/B4C纳米多层涂层的增强增韧机理，从而丰富纳米多层涂层的强韧化理论，为纳米晶-非晶多层涂层的界面优化和性能优化提供理论基础和技术支持。

为突破硬质涂层脆性大的瓶颈，得到高强度高韧性的W/B4C纳米多层涂层，本项目采用脉冲磁控溅射方法制备了不同调制周期和调制比的W/B4C纳米多层涂层，通过分析测试涂层纳米晶-非晶界面的微观结构，揭示界面特征和优界面结合方式，同时测试涂层的硬度、弹性模量和韧性，对涂层进行分子动力学的变形行为研究，研究界面结构对涂层力学性能的影响规律，分析涂层的强韧化机理。.研究结果表明： W/B11C(CBCp)界面具有最大粘附功，其中W(200)/B11C(CBCp)界面为W/B4C纳米多层涂层最稳定界面，界面厚度约为1.6~1.8Å，界面处W原子易失电子，B原子和C原子易得电子，C原子相较于B原子，更易于扩散至界面层。降低调制周期、提高W: B4C调制比，可以有效降低界面粗糙度。二致密度高、粗糙度小、具有良好的层状结构界面有助于涂层的硬度和韧性之间形成良好的平衡关系，获得强度和韧性均较高的涂层。涂层受拉伸时，当W: B4C调制比较大时，剪切转变区域（STZs）很难有效扩展而仅能在非晶相中形成较薄的剪切带，此时模型的塑性变形以晶体层中的相变产生和孪晶形成为主，界面对扩展有明显阻碍作用；W: B4C调制比较小时，STZs存在增殖空间并逐渐形成与拉伸方向呈45°的剪切带胚胎，在拉伸作用下不断增殖并最终扩展为均匀的剪切带，同时伴有晶体相中相变和孪晶的形成。压痕压入涂层，W: B4C调制比较小时，多层涂层中晶体层承受更多的载荷，W: B4C调制比较大时，多层涂层中非晶体层承受更多的载荷，多层涂层中晶体承受严重变形的区域越来越大。并且随着压入深度增加，多层涂层中非晶承受严重变形的区域越来越大。界面协调塑性变形的能力明显。为涂层在原子尺度上的界面优化设计奠定基础，具有重要的理论意义和工程应用价值。