铝合金挤压模防护涂层表面黏着及材料转移微观机理研究

Severe adhesion, material transfer and wear are the key reasons for the short life of aluminum extrusion dies and the poor surface properties of the aluminum extrude. 9 kinds of dense smooth coating of typical materials, which are chosen according to the the bonding energy of Al/coating interface obtained by first-principles study, are fabricated by plasma enhanced magnetron sputtering (PEMS), and then the wetting and adhesion behaviors of aluminum on coating surface will be studied. On the basis of the above study, 5 kinds of the coating systems with an excellent anti-adhesion and corrosion resistance in aluminum liquid will be systematically studied; the coatings with a loose columnar grain, dense columnar grain and dense equiaxial crystal will be fabricated through adjusting PEMS process. And then the growth of aluminum material transfer films on the coatings and thetribological performance of different coatings under various friction conditions will be studied by advanced analysis methods. With a main line of the composition and structure of coatings—the bonding energy of Al/coating interface—the wetting and adhesion behaviors of aluminum on coating surface—the growth of aluminum materias transfer films—tribological behaviors, the influence of the composition and structure of the protective coatings for aluminum extrusion dies on the tribological performance of the extrusion dies and its mechanism will be studied in the project, and then the rules for the R&D and choosing of the protective coatings for the aluminum extrusion dies will be proposed.

严重的黏着、材料转移及磨损是铝挤压模寿命低、铝挤压件表面质量差的主要原因。本项目以解决铝挤压模黏着、材料转移和磨损，延长其使用寿命为目标，首先根据第一性原理计算的Al/涂层界面结合能筛选9种典型涂层材料体系，利用等离子体增强磁控溅射（PEMS）制备出致密、光滑的涂层，并研究铝在典型涂层表面的润湿及黏着行为；在此基础上优选5种抗铝黏着和化学腐蚀性能好的涂层进行系统研究，通过改变PEMS工艺使涂层分别获得疏松柱状晶、致密柱状晶及致密等轴晶结构；在多种摩擦条件下采用先进分析测试技术研究不同成分及结构的涂层与铝合金对摩时涂层表面的铝转移膜生长规律和摩擦磨损性能。本项目以涂层的成分及结构—Al/涂层界面结合能—铝在涂层表面的润湿及黏着行为—涂层表面铝转移膜生长—摩擦磨损行为为研究主线，研究铝挤压模防护涂层成分及结构对挤压模摩擦磨损性能的影响规律及机理，并提出铝挤压模防护涂层研制及选用原则。

铝挤压模是铝型材挤压成形工艺所需的核心工具。苛刻的服役条件导致铝挤压模在使用时容易发生严重的铝黏着和磨损，这是导致铝挤压模寿命低、铝型材表面质量差的主要原因。本项目以改善铝挤压模抗铝黏着和耐磨性、延长其使用寿命为目标，利用第一性原理计算了Al/涂层的界面结合能，探讨了涂层材料体系和表面晶体取向对Al/涂层界面结合的影响；通过调控基体偏流和反应气体流量等参数利用等离子体增强磁控溅射工艺制备出具有疏松柱状晶、致密柱状晶及致密等轴晶结构的TiN、CrN、TiC、TiAlN、TiSiN、CrAlN、CrSiN、TiVN等硬质耐磨涂层，系统考察了涂层沉积工艺-成分-微观结构-力学性能之间的内在联系；考察了不同成分及结构的涂层试样与铝球对磨时的摩擦磨损性能及铝黏着行为，并对涂层试样及铝对磨球的磨斑微观形貌和成分进行了分析，揭示了涂层微观结构和力学性能对与铝球对磨时涂层试样的摩擦磨损和抗铝黏着性能的影响规律及微观机理。结果发现：表面为（100）取向的TiN和TiC涂层的抗铝黏着性能优于（111）取向的TiN和TiC涂层，且（100）取向的TiC涂层抗铝黏着性能更好。随着基体偏流的增加，TiN和CrN涂层的微观结构均由疏松柱状晶转变为致密柱状晶并进而转变为致密等轴晶，硬度H、弹性模量E*、H/E*、H3/E*2等均呈现出先快速升高而后变化不大的趋势；基体偏流对TiN涂层和CrN涂层的成分、相结构及摩擦磨损性能的影响规律存在显著差异。反应气体流量对TiN和TiC涂层结构及性能的影响规律基本相同，但与反应气体流量对CrN涂层结构及性能的影响规律存在显著差异。随着Si含量增加，CrSiN基涂层的微观结构由柱状晶转变为玻璃态；随着V含量增加，TiVN涂层由致密柱状晶转变为致密等轴晶。表面微观织构对与铝球对磨时的涂层表面的铝黏着行为和耐磨性影响很大，具有微凹坑状织构的CrN涂层和微孔结构的TiN涂层比光滑致密的涂层具有更好的抗铝黏着性能和耐磨性。研究成果对铝成形模具和切削刀具的失效机制及延寿技术研发具有重要的借鉴价值。