CrAlVN/CrAlYN纳米多层硬质涂层抗高温氧化、高温摩擦磨损行为及机制研究

During high speed dry cutting, the cutting tools fail because of the oxidation wear, which is due to the high speed friction without lubrication under high temperature. The key route to solve this problem is to improve the high temperature oxidation and wear resistance of the hard coatings on the cutting tools. High wear rate of the self lubrication CrAlVN hard coating due to the fast diffusion of V restricts its applications. It is found that high temperature wear and friction resistance of the CrAlVN/CrAlYN nano-multilayer hard coating are better than those of the single layer coatings. However, the mechanisms behind the results are still unknown. Therefore, this project aims to design and prepare the CrAlVN/CrAlYN nano-multilayer hard coatings with different modulation composition and structure. The influences of the modulation composition and structure on the high temperature oxidation kinetics and tribology properties of the coatings are studied. The high temperature diffusion of the V and Y elements, chemical composition, microstructure and stress state of the oxide scales are analyzed as well as the high temperature evolution of the modulation interface. The mechanisms of the oxide scale growth and oxidation resistance of the coatings are researched. The mechanisms of the high temperature wear and friction resistance of the nano-multilayer hard coatings are explored from the synergistic actions of compactness, self lubrication and wear resistance of the oxide scales and the hard yet tough property of the coatings. The project findings will provide guidance on design and fabrication of hard coatings on the high speed drying cutting tools with superior high temperature properties.

针对高速干式切削时高温、高速摩擦、无润滑的苛刻工况导致刀具因氧化、磨损而失效的问题，研究提高刀具表面硬质涂层的抗高温氧化及摩擦磨损性能是解决的关键。V的迅速外扩散导致CrAlVN涂层显示高温自润滑但高磨损特性，制约其应用。相比单层涂层，CrAlVN/CrAlYN纳米多层硬质涂层具有优异的高温耐磨减摩特性，但相关机理尚不明确。本项目拟设计制备具有不同调制层成分及调制结构的CrAlVN/CrAlYN纳米多层涂层，研究涂层调制层成分及调制结构对涂层氧化动力学及高温摩擦学特性的影响，分析涂层V、Y等组元高温扩散行为、氧化层表/界面成分分布、组织结构、应力状态以及调制结构界面的高温演变规律，揭示涂层表面氧化层生长机理及抗高温氧化机制，从氧化层的致密性、自润滑、高耐磨特性以及纳米多层涂层的既硬且韧性能协同作用出发，探索涂层高温耐磨减摩机理，为具有优异高温性能的高速干式切削刀具涂层的设计制备提供指导。

高速干式切削加工技术由于其高速、高效、高精度以及对环境无污染的优点，代表着未来绿色制造的发展方向。但高温、高速摩擦、无润滑的苛刻使役条件导致刀具因氧化磨损而失效，刀具表面硬质涂层是实现高速干式切削加工的关键。近年来，CrAlN硬质涂层因其良好的抗高温氧化及耐磨性能备受关注，但仍然不能满足高速干式切削加工技术的发展和难加工材料的日益增多对涂层高温性能提出的更为苛刻的要求。本项目采用磁控共溅射技术结合基体旋转、挡板设计，制备了不同成分及调制结构的CrAlN基多元/纳米多层，通过对涂层的成分、微观结构、表面力学、抗高温氧化以及摩擦磨损性能的综合表征，系统研究了涂层制备工艺、成分调控及调制结构对涂层组成、结构及性能的影响，研究结果表明：涂层的生长结构演变取决于沉积粒子数量、种类、能量及其表面扩散行为；富Al且结构致密的(AlCr)2O3氧化层，有效降低了氧气的内扩散，使得CrAlN涂层具有优异的高温抗氧化性能，但当温度高于1150℃时，富Cr且粗大多孔的(AlCr)2O3氧化层，导致涂层高温抗氧化性能急剧下降；Y在氧化层/氮化层界面处的偏聚，钉钆了界面处的位错，降低了界面处点缺陷数量，限制了Cr、Al阳离子的外扩散速率，使得CrAlYN涂层（0.6-1.5at.%Y）具有优异高温抗氧化性能。但超过1.5at.%Y的掺入，导致氧化层内粗大的YAG第二相生成，急剧降低了CrAlYN涂层的高温抗氧化性能；CrAlN涂层高温抗氧化性能随V元素的掺入量增加而急剧降低，严重限制其在高温抗氧化及耐磨工况下的应用；通过优化CrAlVN/CrAlYN纳米多层硬质涂层的制备工艺、成分及调制层结构，使得涂层表面氧化层兼具致密性、自润滑以及高耐磨特性，从而有效地提高涂层抗高温氧化及高温摩擦磨损性能；750℃摩擦磨损测试时涂层的摩擦系数为~0.3，磨损率为0.9-1.5×10-6mm3/Nm。本项目取得的主要研究结果丰富了硬质涂层高温氧化和摩擦磨损理论，对指导具有优异使役性能的高速干式切削刀具涂层的设计制备有着重要的实际应用价值。