铝合金表面原位自生(Ti,Cr)N/Al-(Ti,Cr)多层复合结构调控与摩擦学行为研究

As main materials for lightweight manufacturing, aluminum alloys show low hardness and poor wear resistance. Thus, a duplex surface treatment involved with depositing followed by plasma nitriding is proposed based on the idea of thermo diffusion alloying. Nano Ti-Cr films are prepared on the surface of aluminum substrates as diffusion sources by using magnetron sputtering. Then, (Ti,Cr)-N and (Ti,Cr)-Al reaction will be motivated simultaneously by using plasma nitriding to in situ fabricate nano (Ti,Cr)N compound/Al-(Ti, Cr) multilayer coatings. First principles calculations combined with the thermo calculations are employed to study the possible formation phase, the corresponding structure stability and mechanical properties, providing the foundation for the component design of multilayer coatings. Effects of the composition, growth orientation and grain size of Ti-Cr films as well as nitriding parameters on the microstructure evolution of the multilayer coatings are investigated. The growth kinetics of the multilayer coatings will be established. EPMA/EBSD/TEM are employed to analysis the elements distribution, phase structure and growth orientation of the multilayer coatings, thus revealing the interface layer growth mechanism. Combined with the analysis of the friction coefficient, wear rate and the wear surface and debris under different wear stages, the wear mechanism of multilayer coatings will be clarified. The above studies will contribute to the theoretical and technical support for designing and microstructure controlling of the wear-resistant coatings on the surface of aluminum alloys.

铝合金是零部件轻量化制造的主要材料，针对其表面硬度低和耐磨性差的问题，本项目基于扩渗合金化思想，提出镀/渗复合表面改性方法，通过磁控溅射在铝合金表面预置纳米晶Ti-Cr膜作为扩散源，再等离子渗氮，实现(Ti, Cr)-N和(Ti, Cr)-Al扩散反应的同时进行，原位制备出纳米(Ti, Cr)N/Al-(Ti, Cr)多层复合层。采用热力学和第一性原理计算预测反应生成相的形成可能性、结构稳定性及力学性质，为多层结构的组元设计提供依据；研究Ti-Cr膜的成分、生长取向、晶粒尺寸和渗氮工艺对复合层组织结构演变的影响规律，建立复合层的生长动力学方程；利用EPMA/EBSD/TEM分析各层元素分布，物相结构和生长取向，揭示界面反应层的微观形成机制；研究复合层摩擦系数和磨损率的变化规律，结合磨痕和磨屑的形貌和成分分析，阐明复合层的磨损机理，为铝合金表面耐磨层的设计和组织结构调控提供理论和技术支撑。

铝合金是零部件轻量化制造的主要材料，但存在表面硬度低和耐磨性差的问题。本项目采用第一性原理计算预测了三元相Ti-Cr-N和Al-Ti-Cr的形成可能性、结构稳定性和力学性质，获得了Cr含量与三元相性质的对应关系，依据优化的物相结构和铝合金基体的性能匹配，提出硬质氮化物/铝化物的复合层结构设计。本项目将两种传统表面处理技术磁控溅射和等离子渗氮相结合，形成了镀渗复合处理技术，通过磁控溅射在铝合金表面预置纳米晶Ti-Cr膜作为扩散源，再等离子渗氮，同时激发Ti-Cr/N和Ti-Cr/Al之间的反应扩散，实现了氮化物/铝化物复合层的原位制备，与基体形成冶金结合。溅射镀膜研究表明：不同Cr含量的Ti-Cr膜均为β-Ti (BCC)结构，沿(110)面择优生长，表面颗粒呈球形，晶粒尺寸均小于100 nm，随着Cr含量的升高，膜层更加致密，颗粒球形度增加，晶粒尺寸减小，Ti-Cr膜的硬度升高；偏压对Ti-Cr膜的组织形貌和性能影响不明显，高偏压下获得的膜层致密度增加。等离子扩渗研究表明：低偏压(-10V)和低Cr含量(<25 at.%)制备的Ti-Cr膜经渗氮后表面物相主要为(Ti,Cr)N0.3相，高偏压和高Cr含量渗氮后主要为 (Ti,Cr)N相，随着渗氮温度和气氛中含N量升高，表面(Ti,Cr)N相含量增多；复合层为三层结构，最外层为Ti-Cr-N层，中间层和里层为铝化物层，分别为Cr掺杂的Al3Ti层和Al18Ti2Mg3层。经过镀渗复合处理，铝合金表面硬度明显提高，可达1040 HV；摩擦系数减小，可达0.32，磨损率明显下降，提高了耐磨性；揭示了复合层的磨损机制，表面(Ti,Cr)N0.3相含量较高时，为严重的粘着磨损和轻微的磨粒磨损，表面主要为 (Ti,Cr)N相时，表现为明显的磨粒磨损，复合层均从初期的粘着磨损向稳定阶段的磨粒磨损转变，并伴有氧化磨损。本项目的复合层制备技术将为有色金属表面新型防护层的设计和制备提供理论和技术基础。