外加颗粒在线喷丸对冷喷涂金属沉积体微结构的原位优化及机理

In cold spray, materials are deposited through plastic deformation of spray particles in completely solid state via high velocity impact. Consequently, problems such as oxidation, grain growth and phase transformation inherent to the conventional thermal spray can be minimized or eliminated, which makes cold spray a potential process to deposit high quality metallic materials, especially for metals with unequilibrium microstructure...Mechanical properties of cold sprayed deposits are significantly affected by the deposit porosity and inter-particle bonding. So far, there are mainly two effective approaches to decrease the deposit porosity and improve the inter-particle bonding: improving the particle velocity and raising the particle temperature. However, to substantially improve the impact velocity, the costly Helium gas should be used to accelerate the spray particles. Meanwhile, high particle temperature always results in fouling of the Laval nozzle and microstructure and composition change for heat sensitive materials. On the other hand, although work hardening and grain refining formed during the particle deposition is potential to remarkably improve the material strength. However, the work hardening and grain refining formed during high velocity impact only locates at/near inter-particle boundaries in conventional cold sprayed metallic deposits, which makes those strengthening effects can not contribute much to the mechanical properties of the cold sprayed deposit. Therefore, in this study, big sized stainless steel particles were added into the spray powders as shot peening powders to increase the plastic stain of the deposited particles. It is attempted that the inter-particle bonding will be in-situ improved and the porosity will be in-situ decreased by the shot peening induced enhanced plastic deformation of the deposited particles. Meanwhile, by the shot peening induced enhanced plastic deformation, it is expected that the strengthening effects located only at particle boundaries can be expanded to the entire particle...In this work, the influence of shot peening on the deposition behavior of the spray powders and microstructure of the cold sprayed deposit will be systematically investigated. Effect of shot peening intensity on plastic deformation behavior (stain and temperature fields) of the deposited particles will be studied both experimentally and numerically. Detailed microstructure characterization and mechanical properties measurement will be carried out to clarify the correlation of particle deformation level and its uniformity to the inter-particle bonding and strengthening effects in cold sprayed metallic deposits. It was expected that this work can provide a new approach to prepare metallic deposit of high quality by cold spray with low-cost.

冷喷涂沉积体的致密度及粒子间结合对其性能有显著影响。迄今为止，提高致密度与粒子间结合要通过提高粒子温度或以昂贵的氦气显著提高粒子速度来实现。而提高粒子温度存在粉末堵塞Laval喷管及温度敏感材料成分、微结构变化的问题。另外，粒子沉积中形成的位错增殖和晶粒细化有使材料强度进一步提升的潜力。但粒子内部塑性应变的不均匀性使这些强化效应仅分布在粒子界面附近，难以对整体材料的强度产生显著贡献。目前，除纯Cu可依靠自身碰撞实现大应变塑性变形的均匀化使其强度显著高于冶金块材外，其它材料均未见类似报道。针对以上问题，本研究提出通过外加颗粒的在线喷丸提高已沉积粒子的变形程度及变形均匀性的新思路，原位实现沉积体致密化、粒子结合强化及强化效应在粒子内分布范围的扩大。控制喷丸颗粒速度，避免对沉积体造成污染和严重冲蚀。阐明粒子变形量及均匀性与粒子结合、原位强化这一关键问题，为通过冷喷涂制备高性能金属沉积体提供依据。

冷喷涂是一种通过微米尺度的沉积颗粒在超音速条件下撞击基体表面，通过固态条件下粒子与基体界面处剧烈的塑性变形实现粒子结合的材料沉积技术。较低的沉积温度使冷喷涂能够在大气条件下避免金属材料在沉积过程中发生氧化，因此，冷喷涂是制备高性能金属合金及金属基复合材料涂层及增材制造的潜在有效方法。但是常规条件下冷喷涂材料制备中，沉积粒子有限的塑性变形量会导致沉积体产生致密度较低及性能较差的问题。然而，目前尚无有效的低成本解决途径。. 针对以上问题，本课题提出通过外加颗粒的在线喷丸提高已沉积粒子的变形程度及变形均匀性的新思路，原位实现沉积体的致密化、粒子结合的强化。采用Ti、TC4、 Ni、Cu及Al基合金粉末，通过实验结合数值模拟的方法确立了不引入污染的喷丸条件窗口；研究了外加喷丸颗粒的喷丸效应对沉积体显微结构和性能的影响规律，揭示了喷丸效应对沉积体的原位致密化机理；研究发现了外加喷丸颗粒可使沉积粒子内部大范围内实现晶粒原位细化的现象。在此基础上，基于可控的喷丸效应诱导动态再结晶机制，确立了一种通过原位喷丸辅助冷喷涂制备高致密度、超细晶金属材料涂层及块材的固态冶金方法。以Cu和Ni为例，阐明了喷涂粉末的显微结构与自身喷丸效应的关联性及对粒子沉积特性的关联性，在此基础上，提出了一种采用混合不同结构粉末利用自身喷丸效应沉积高致密度金属的沉积方法。基于发现的纳米结构金属基陶瓷复合材料沉积过程中粒子自身喷丸效应导致金属/陶瓷界面形成纳米尺度高密度晶体缺陷层的现象，提出了一种低温烧结条件下实现金属/陶瓷界面调控的方法。研究成果可为高导热、高导电、高耐腐蚀性金属合金涂层及高致密度超细晶金属材料的增材制造提供理论指导和新的途径。. 该项目发表SCI收录期刊论文4篇，国际会议论文5篇，申请发明专利4项；培养硕士生2名，博士生2名，其中1名硕士和1名博士已获得学位；项目金额25.0000万，支出14.1132万，剩余10.8868万，剩余经费用于该项目后续研究。