超厚硬质薄膜的内应力调控及动态结合性能研究

There are some progresses on technique of ultra thick coatings with thickness of tens or hundreds micrometers, and further enhanced attentions has paid on the mechanical properties of thin films, especially interface bonding strength and fracture toughness. At present, although researchers have been mostly concentrated on the realization of large thickness of the deposited thick hard coatings,they have begun to realize that thickening and regulation mecahnism are key factors of hindering application of hard coatings. In this project, nano-composite TiAlSiCN coatings and nano-layer TiAlSiCN/Ti composite coatings with ultra thickness are prepared by vacuum vapor deposition methods, and effect of nanometer structure optimization and layered stress release on the great increase of film thickness is studied; The fracture toughness and dynamic adhesion properties on interface of hard coatings with ultra thickness are studied by indentation and contact fatigue methods; Comparing with indentation method and the scratch method, the models of static and dynamic adhesion characterization are built for hard coatings with ultra thickness; Combined with charaterzation of the feature microstructure and internal stress of the coatings, the mechanism of cracking and delamination of hard coatings with ultra thickness prepared by vapor deposition will be revealed. The research will provide a theoretical and practical support for the deposition of thick coatings with high adhesive strength and toughness on surface of metal, and also for the modulation of internal stress in coatings.

厚度数十甚至数百微米的硬质薄膜在技术上已有所突破，进一步增强了人们对薄膜力学性能特别是界面结合强度和薄膜断裂韧性的持续关注热度。尽管超厚硬质薄膜的研究目前仍主要集中在超厚尺度的实现途径上，但人们已开始认识到硬质薄膜的增厚机理及其调控机制已成为制约其进一步发展和应用的关键因素。本项目拟通过气相沉积超厚多元复合TiAlSiCN和多层复合TiAlSiCN/Ti纳米硬质薄膜，研究纳米结构优化和层状应力缓释对膜厚大幅增加的效果；基于压入法和接触疲劳法，探究超厚硬质薄膜的断裂韧性和界面结合性能表征；比照传统的静态压入法和划痕法，建立随膜厚增大薄膜静态和动态结合性能的表征模型；结合薄膜特征结构分析及内应力测试，阐明气相沉积超厚硬质薄膜在特定条件下开裂和剥落的本质属性。为金属材料表面强附着、高韧性、大厚度的气相沉积硬质薄膜的微结构设计及内应力调控提供理论和实验参考。

薄膜内应力是制约气相沉积硬质厚膜开发和应用的关键因素之一。研究厚膜内应力工艺调控参数及机理，并通过层状结构优化薄膜组织和内应力，是获得强结合、高韧性、大厚度气相沉积硬质薄膜的重要途径。本项目以TiN基硬质薄膜为主要研究对象，研究氮化物硬质薄膜厚度与组织的关系，探讨超厚硬质薄膜断裂韧性的评价方法，探究影响薄膜内应力形成的因素及调控手段，建立硬质薄膜动态结合强度的定量表征，进而阐明硬质薄膜在外加载荷和内应力共同作用下薄膜剥落的本质。研究表明，多弧离子镀单层膜柱状晶组织随厚度增大而粗化，多层膜可有效细化晶粒；韧性金属基体上超厚膜的断裂韧性可以通过四棱锥压头小载荷多次压入结合大载荷一次压入的方法获得，具有粗大柱状晶组织的薄膜断裂韧性较低；硬质膜内应力以组织应力为主，通过偏压和气压参数减少沉积粒子的能量输入可降低薄膜残余压应力；提出了引入一定塑性变形的陶瓷球滚接触疲劳和球形压头多次压入等动态结合强度评价方法，可有效促成薄膜沿界面的剥落，并得到薄膜剥落时膜基界面疲劳强度的定量表征，所得结果能够明显反映膜基界面状态差异，而且不受膜厚等非界面因素影响；基片弯曲法测得的薄膜内应力随厚度增大而降低，但采用有限元模拟方法计算得到的残余应力在膜基界面产生的切应力数值仍然为增大的趋势，较高的内应力在膜基界面处引入的切应力使较低的外加载荷下即出现薄膜剥落。本项目的研究揭示了气相沉积硬质膜残余应力随薄膜厚度的演化规律，探明了残余压应力对膜基动态结合强度的作用机制，所提出的膜基动态结合强度评价方法和超厚硬膜断裂韧性评价方法扩展了硬质膜力学性能定量评价范围，对于硬质厚膜的设计、制备和应用具有重要的指导意义和实用价值。