搅拌摩擦加工镍铝青铜合金耐腐蚀疲劳组织优化及机理研究

Friction stir processing (FSP) is one of the most effective ways to solve the problem of serious corrosion fatigue damage of nickel aluminum bronze (NAB) alloy. Obtaining optimum microstructures with the best corrosion fatigue resistance and revealing its corrosion fatigue mechanisms are the key issues in this field needing to be resolved at present. Therefore, in this project, four typical microstructures of FSPed NAB alloy and their corrosion fatigue behaviors are the main study object. EBSD characterization of corrosion fatigue growth path is performed to understand the crystallographic features of crack growth. Based on quantitative microstructure analysis and fracture observation of corrosion fatigue crack growth path, the response relation between microstructural state and corrosion fatigue properties is revealed, and then superior order of various microstructures of corrosion fatigue resistance is ensured. For understanding crack tip oxidation and material transmission law, phase structures and chemical composition of material around corrosion fatigue crack tip are determined by TEM assisted by FIB, and quantitative analysis of chemical composition on crack propagation path is performed. Mechanical mechanism of plastic deformation in crack tip is revealed via finite element modelling and experimental characterization of crack tip plastic area. Finally, based on above analysis, corrosion fatigue mechanisms of FSPed NAB alloy are revealed. The achievements obtained in this project can provide theoretical support for microstructure modification of NAB alloy.

搅拌摩擦加工是解决镍铝青铜合金严重腐蚀疲劳破坏问题的最有效途径之一，获得搅拌摩擦加工镍铝青铜合金耐腐蚀疲劳性能的理想组织，并阐明其腐蚀疲劳机理是该领域亟待要解决的关键问题。因此，本项目围绕搅拌摩擦加工镍铝青铜合金四种典型组织的腐蚀疲劳行为开展研究工作，采用EBSD技术对腐蚀疲劳裂纹扩展路径进行表征，掌握腐蚀疲劳裂纹扩展的晶体学特性，基于裂纹扩展路径的显微组织定量分析和断口观察，阐明组织状态与耐腐蚀疲劳性能的响应关系，确定各组织的耐腐蚀疲劳优劣顺序，通过FIB辅助TEM探究裂纹尖端周围物质的组织结构和化学成分，并结合裂纹路径上物质化学成分的定量分析，明确裂纹尖端氧化和腐蚀产物传送规律，利用裂纹尖端塑性区的有限元模拟和实验表征，阐明裂纹尖端塑性变形的力学机理，最终揭示加工合金的腐蚀疲劳机理，为镍铝青铜合金的组织调控提供理论指导。

镍铝青铜合金是目前海洋装备螺旋桨的最主要材料，在海洋中服役过程中很容易发生腐蚀疲劳破坏，而搅拌摩擦加工可以同时提高合金机械和耐腐蚀性能，在提高合金腐蚀疲劳性能上具有很好的应用前进，本项目针对搅拌摩擦加工镍铝青铜合金典型的微观组织，开展腐蚀疲劳组织优化和腐蚀疲劳机理的研究工作。研究发现均匀细小的等轴组织具有最好的抗腐蚀疲劳性能，而魏氏体组织具有最差的腐蚀疲劳性能。通过腐蚀疲劳裂纹尖端的材料学、材料-化学反应和力学三个方面，系统研究了搅拌摩擦加工抗腐蚀疲劳机理，研究表明，在腐蚀疲劳的过程中，搅拌摩擦加工合金主裂纹周围的βˊ相因发生脱铝反应而发生严重的破坏，这主要是因为在腐蚀疲劳的过程中，裂纹里面溶液的酸化和应力场的耦合作用使裂纹尖端各相形成的保护膜不稳定、破坏或者溶解，βˊ相作为阳极被腐蚀掉。腐蚀疲劳裂纹尖端在低ΔK和高ΔK展现不同的腐蚀疲劳行为，降低搅拌摩擦加工的热输入，形成均匀细小且少βˊ相的组织可以提高搅拌摩擦加工合金的耐腐蚀疲劳性能。本项目阐明了搅拌摩擦加工镍铝青铜合金组织和耐腐蚀疲劳性能响应关系，优化加工合金的组织结构，并揭示其腐蚀疲劳机理。在该基金的支持下，发表高水平论文10篇（SCI9篇，EI1篇），申请发明专利2项（授权1项），对于提高海洋装备服役寿命具有重要现实价值和理论意义。