冷喷涂颗粒增强铝基复合涂层硬质相临界沉积模型及两相共沉积机制研究

Cold spraying has great potential use of its low-temperature deposition to adjust particle-reinforced metal matrix composite coating for applications of repair and re-production of damaged advanced parts in aerospace and railway areas. To solve the difference in the reinforcement content between in the composite coating and in the feedstock powders due to the great deposition difference of metal and reinforcement particles, exploring the main factors which control the homogeneous distribution and content of the reinforcement particles in the coating could be the principal issue to realize the control of coating property. And the critical deposition mechanism of the hard particles could be the key point to the question. Therefore, this project intends to study the acceleration behavior of the hard particles during the deposition process and the effect of metal and hard particle deposition behavior on reinforcement content and distribution in cold sprayed particle reinforced Al based composite coatings, basing on fixing the process parameters of the critical deposition condition of the metal particles, in addition of powder design and numerical simulation methods, aiming at clarifying critical deposition condition of the reinforcement particles and co-deposition mechanism of the metallic and reinforcement phase in the composite coating. The implementation of the project could be of important significance in improving the theory of cold sprayed composite coating, the preparation of high performance metal matrix composite coating and its extended application in aerospace and rail transit.

冷喷涂技术的低温固相沉积特点使其制备的颗粒增强金属基复合涂层直接用于航空、轨道交通零部件维修有巨大应用潜力。为解决冷喷复合涂层时因金属颗粒与硬质相颗粒的沉积效率差异较大，导致硬质相颗粒在涂层中含量与在喷涂粉末中的含量存在差异，从而偏离设计成分，影响冷喷涂复合材料性能有效调控的不足，需研究影响复合涂层硬质相含量及分布的主导因素，探讨硬质相临界沉积机理。因此，本项目以冷喷涂颗粒增强铝基复合涂层为研究对象，通过选定以达到金属颗粒良好沉积的工艺参数，简化喷涂工艺的复杂影响，并通过硬质相粉末设计并结合数值模拟方法，重点研究冷喷涂过程中硬质相飞行加速行为以及金属与硬质相粉末的沉积行为对涂层中硬质相含量及分布的影响，揭示硬质相的临界沉积条件以及复合涂层中金属相粒子和增强相粒子的共沉积机制。该项目的实施将对完善冷喷涂复合涂层理论、制备高性能金属基复合涂层及其在航天航空、轨道交通的推广应用都具有重要的意义。

冷喷涂技术已在航空零件尺寸修复中得到了重要的应用。采用冷喷涂技术在制备复合涂层时，可通过改变喷涂粉末中硬质相来实现复合涂层性能的调控，但因金属颗粒与硬质相颗粒的材料特性差异较大，其各自的沉积效率不同，最终导致硬质相颗粒在涂层中含量与在喷涂粉末中的含量存在差异，偏离设计成分。这必将制约冷喷涂复合材料性能的有效调控的优势。因此如何调控涂层中硬质相的含量和分布是实现冷喷涂复合材料性能调控的首要问题。.研究证实对于硬质相在飞行过程中的损失和硬质相颗粒撞击到已沉积在金属相中的硬质相颗粒时不发生沉积甚至致使已沉积颗粒的脱落/破碎是导致硬质相颗粒在涂层中含量一般低于喷涂粉末中的含量的主要原因。此外，硬质颗粒的临界沉积条件并非“临界速度”，试验发现，硬质相颗粒的“临界动能”为硬质相进入涂层沉积的条件。.对于硬质相在涂层中均匀性研究表明，硬质相在涂层中的均匀分布于同质硬质相尺寸存在反关系；对于同质不同含量硬质相涂层，一般认为硬质相体积比为25vol.%时，涂层中陶瓷颗粒分布最均匀；对于不同质硬质相增强复合涂层，当颗粒直径相当，硬质相密度相当时，其均匀性也相当，高密度硬质相引入较差的均匀性。.对于金属与增强相共沉积机制，粉末中的硬质相颗粒会增加硬质相颗粒之间的碰撞，从而以碎屑的形式消散其他动能，从而对变形的金属颗粒进行喷丸处理颗粒随后被削弱。硬质相的强度降低和裂纹的出现在一定程度上可以降低涂层的残余应力，从而导致金属相颗粒残余应力降低。当超过金属相颗粒破碎阈值时，破碎的颗粒被保留在涂层中，并以分散的方式强化了金属颗粒，从而导致残余应力的增加。另一方面， 金属颗粒的较高残余压应力又有利于涂层中硬质相的沉积。