离子束原位合成Al2O3-TiB2-TiN增强高熵合金涂层的结构演化及高温磨损机理

Aiming at the key difficult issue of rapid wear loss of some key machinery parts or components such as the braking discs of high-speed trains due to the friction and wear at high temperature, this project devotes to in-situ synthesize the Al2O3-TiB2-TiN/CoCrCuFeNi high entropy alloy coating based on the advanced materials design and plasma arc cladding system. The criterions for the chemical composition and structure design of coating precursors are proposed based on the detailed investigation of the formation and evolution of microscale and nanoscale structures in Al-BN-TiO2/CoCrCuFeNi reaction system at rapid non-equilibrium solidifying conditions. The flow behaviors of molten pool and the effects of atomic diffusion and transportation behaviors on the grain orientation, distribution, refinement and interface configuration mechanisms of coatings are explored accordingly. The multi-scale deformation and damage behaviors at microscale and nanoscale conditions are clarified in order to reveal the physical nature of the energy dissipation and loss of the coatings. The structure-activity relationship and toughening mechanism for the coatings are investigated. The oxidation and structural evolution behaviors at high temperature of the as-prepared coatings are studied. The mechanisms for the structural evolution and damage of high-entropy alloy coatings during friction and wear process at high temperature are discussed. The damage and failure models are constructured by considering the materials and structure of coatings, and coupled actions of heat, applied load and chemical reactions. This project can provide some theoretical insights on the protection and life-prolongation design of key hot end components of advanced equipments.

针对高速列车制动盘等关键零部件因高温摩擦导致快速磨损的技术难题，本项目基于先进的材料设计和等离子束系统原位合成Al2O3-TiB2-TiN/CoCrCuFeNi高熵合金涂层。系统研究Al-BN-TiO2/CoCrCuFeNi反应体系在快速非平衡凝固条件下涂层微纳结构的形成及演化规律，建立涂层前驱体成分和结构优化设计准则；探明熔池流动行为及原子的扩散迁移对涂层晶粒取向、形态分布、组织细化和界面构型的影响规律，澄清涂层结构演化和界面作用机制；探究涂层在微/纳多尺度下的变形和损伤行为，明晰涂层能量耗散和失稳的物理本质，揭示涂层构效演变和复合强韧化机制。研究涂层在高温环境下的氧化及结构演化行为，澄清高温摩擦磨损过程中高熵合金复合涂层的结构演变与损伤机理，建立包含涂层材料、结构及热-力-化学效应且物理意义明确的损伤及失效模型，为我国先进装备关键热端零部件的防护与延寿设计提供理论支持。

针对高端装备关键零部件的高温磨损防护及延寿需求，本项目致力于多元陶瓷原位析出增强高熵合金复合涂层成分设计、成形机理、组织调控及高温磨损机理研究。基于多元陶瓷相原位析出及高熵合金固溶体形成热力学/动力学原理，优化设计了CoCrFeMnNi(Ti, V, Nb)、CoCrFeMnNi/(Ti，BN)x、CoCrFeMnNi/(Al，TiO2，BN)x和FeCoNiCuAl/(Al，TiO2，BN)x高熵合金粉末材料。利用等离子熔覆技术制备了Ti、V、Nb合金化高熵合金涂层和TiN-Cr2B、Al2O3-TiN-Cr2B、Al2O3-TiN-TiB2多元陶瓷增强高熵合金复合涂层，揭示了高熵合金复合涂层形成机理。结果表明，Ti、V、Nb合金化可促进涂层由FCC结构向BCC结构转变，诱发形成Sigma相或Laves相，细化晶粒并提高涂层的硬度和耐磨性。复合涂层跨尺度多元陶瓷相呈较均匀的弥散分布，TiN和Al2O3呈微纳尺度颗粒形貌，部分TiN优先包覆于Al2O3生长；Cr、Ti与B之间结合具有竞争效应且Cr优先于Ti；TiB2、Cr2B陶瓷相沿晶界或FCC和BCC相界面析出；多元陶瓷相间存在部分共格界面，能够抑制涂层枝晶结构形成并细化晶粒，其强韧化机制主要为弥散强化、细晶强化和固溶强化。系统研究了涂层了高温磨损行为，结果表明多元陶瓷增强高熵合金复合涂层摩擦系数稳定性和耐磨性能均优于纯高熵合金涂层，高温耐磨性提高1.34~9.98倍，复合涂层的耐磨性随着陶瓷含量的增多而提高，其磨损机理主要为磨粒磨损、氧化磨损、粘着磨损和疲劳损伤。原位析出多元陶瓷相能有效抑制涂层磨痕亚表层微裂纹的萌与扩展，提升涂层在应力-热耦合作用下的塑性变形抗力及抗氧化特性，基于此构建了涂层在载荷-环境耦合作用下的磨损损伤模型。本项目研究结果能够为先进装备关键热端零部件的高温磨损防护提供理论和技术支持。