等离子喷涂金属涂层粒子间冶金结合增强与机制的研究

It is well known that there exists only a limited bonding between splats in both thermal spray metal and oxide coatings, which dominates their coating properties and performance. The possible oxide film evolved on metal splat surface during deposition makes it more difficult to improve metal coating cohesion and even investigate lamellar interface bonding nature than ceramic coating. Thus, there is no any effective approach to enhance the bonding between lamellae in the as-sprayed metal coatings yet. Based on the lasted advances on the relationship between the splat critical bonding temperature and ceramic material properties and taking account of obtainable wide temperature range of molten metal droplets in plasma spraying, in the present project it is proposed to investigate the effect of deposition temperature on the inter-lamellae bonding to the oxide-free metal surface and oxide-covered surface but at different thicknesses using vacuum plasma spraying system. The splats will be deposited with the molten droplets at different temperatures on the substrate with the identical compositions to splat at different deposition temperature to simulate the intersplat bonding formation. The bonding nature will be examined by HR-TEM through FIB-sampled dedicate interface samples. The investigations are aimed at clarifying the effect of deposition temperature on the splat bonding formation to both oxide-free and oxidized substrate, effect of oxide film on the bonding formation, interface bonding nature and mechanisms involved. The study also focuses on the molten conditions to cause the substrate surface layer melting and disperse the oxide film on substrate surface on impact to form metallurgical bonding. Thereafter, the bond formation mechanisms will be clarified. The formation mechanism of a metallurgical bonding between impacting droplet and identical substrate will be ascertained to propose a new approach to significantly increase the lamellae bonding ratio in thermal spray metal coatings. Moreover, the relationships between lamellar bonding ratio and typical coating properties will be established to provide a guideline for increasing lamellar interface bonding ratio, the performance of plasma-sprayed metal coating and consequently provide an effective solution to the bonding enhancing problem for extending application fields of thermal spray metal coatings.

热喷涂金属涂层与陶瓷涂层同样具有层状结构特征，其层间有限的结合控制着涂层性能。与氧化物陶瓷涂层不同之处在于，大气氛中喷涂金属涂层时金属粒子表面可能出现氧化膜，使得界面形成金属冶金结合过程更加复杂。本项目基于等离子喷涂陶瓷粒子形成结合存在临界温度的最新研究进展与金属熔融粒子温度可大幅度调控的特点，提出了通过真空等离子喷涂实现在有氧化膜、氧化膜厚度可控的条件下沉积扁平粒子，采用FIB制样与HR-TEM研究金属粒子界面结构与结合形成规律的思路。研究阐明无氧化膜下沉积温度对金属粒子界面结合形成规律与机制、氧化膜厚度对粒子界面结合形成规律与结合性质的影响规律、高温熔滴碰撞引起同质材料表面微区熔化与分散基体表面氧化膜的规律与机制，揭示金属熔滴碰撞形成冶金结合机制。为理解至今尚未解决的大幅度提高等离子喷涂金属涂层粒子界面结合的难题、通过调控粒子界面冶金结合比率显著提高涂层性能提供新的方法。

本项目的目标为以等离子喷涂金属涂层粒子界面结合调控规律及其机制为研究对象，在研究阐明无氧化条件下沉积温度对金属粒子界面结合形成规律与机制的基础上，研究氧化膜厚度对粒子界面结合形成规律与结合性质的影响、高温熔滴碰撞引起同质材料表面微区熔化与分散基体表面氧化膜的规律与机制，揭示金属熔滴碰撞形成冶金结合的条件与机制，为调控涂层粒子界面冶金结合比率提供依据。. 为此，采用NiCr合金粒子在氩气保护的低压等离子喷涂环境中沉积扁平粒子，阐明了基体温度对粒子界面结合形成、界面结构与性质的影响规律，发现即使沉积温度增加至550oC，粒子与基体结合率仍约为40%，即提高沉积温度并不能显著增加界面结合的特征。通过对基体预氧化控制，阐明了基体表面氧化膜厚度对界面结合的影响规律与影响机制，发现当表面氧化膜增厚而引起粗糙度显著增加时，将显著降低界面结合率，而高温液滴破碎氧化膜是形成冶金结合的条件。阐明了元素蒸发是控制传统Ni基合金颗粒在等离子焰流中加热温度的关键因素，而熔滴温度难以提升又是制约界面冶金结合难以增加的关键控制因素；首次提出了采用Mo包覆Ni基合金粒子核壳结构粉末设计大幅度提高熔滴温度的方法，系统研究基于粉末设计可粒子温度提升至接近其沸点的高温，获得了熔滴碰撞自冶金连接效应，从而使界面结合从传统的约40%提升至80%以上，由此，提出了基于高温熔滴创制自冶金连接效应显著提升粒子界面冶金结合、从而通过等离子喷涂制备以冲蚀行为为代表的力学行为与块体材料相当的涂层制备方法，进一步发展了结合冷喷涂喷丸致密化方法实现完全消除NiCrMo涂层贯通孔隙，从而获得完全耐腐蚀性能的涂层制备方法。. 研究结果不仅为理解界面冶金结合的形成规律与机制提供依据，也为解决至今未解决的大幅度提高金属涂层粒子界面结合的难题、从而显著提高涂层性能提供了新方法。基于研究成果，已发表论文14篇，其中期刊论文7篇，国际会议论文7篇；申报发明专利3件，其中获授权2件。