纳米组织WC-η复相涂层的耐熔锌磨蚀机理研究

Thermal sprayed WC-Co cemented carbide coatings have played an irreplaceable role in protecting the large mechanical equipments from surface wear and corrosion. However, the Co phase easily corroded in environment of molten zinc, leading to early failures of coatings. This project proposes to develop a new nanostructured WC-based coating with excellent wear-corrosion resistance to molten zinc through the synthesis of nanoscale WC and corrosion-resistant Co-W-C compounds i. e. η phase as an alternative to Co by in situ reactions of metal oxides and carbon, and the simultaneous grain refinement of coating to improve its strength and toughness and thus the resistance to cracks initiation and propagation. On this basis, the mechanisms of the in situ synthesis and the phase stability control during the high-temperature thermal spraying of nanoscale WC-η composite will be clarified. Moreover, we try to obtain the mechanisms of the atomic migration at the interface between nanocrystalline coating and molten zinc, the effect of molten zinc on the initiation and propagation of cracks of the coating and the influence of the phase constitutions and microstructures of coatings on their wear-corrosion resistance to molten zinc. Accordingly, the key mechanisms for the wear-corrosion resistance of the nanostructured WC-η coating against molten zinc will be proposed. The proposed new techniqul mechanisms are expected to enrich the corrosion-resistant theories of nanomaterials and break the peak performance of the current WC-based coatings as well as provide scientific basis for the research and development of cermet coatings applicated in other severe conditions.

热喷涂WC-Co硬质合金涂层在大型机械装备表面耐磨、耐蚀防护上具有不可替代的重要作用，然而在熔融锌等环境中Co相极易遭受腐蚀而导致涂层过早失效。本项目提出利用金属氧化物与碳的原位反应合成纳米WC和耐锌液腐蚀的Co-W-C化合物即η相以替代单质Co，同时通过纳米晶粒组织的强韧化效应提高制备涂层中裂纹的形核扩展抗力，研制在熔锌中具有优良耐磨蚀性能的新型纳米WC基涂层。在此基础上，揭示纳米WC-η复相的原位生成及高温热喷涂时的稳定性控制机理；研究纳米组织涂层/熔锌界面处原子的迁移规律、熔锌对涂层内裂纹形核和扩展的作用机制以及涂层相组成和微结构与其耐熔锌磨蚀性能的关系规律，由此提出纳米组织WC-η复相涂层在熔锌环境中的耐磨蚀机理。本项目提出的新技术机理可丰富纳米晶材料的耐蚀性理论，并有望显著提高现有WC基涂层在熔锌环境中的服役寿命，为其他面向苛刻环境应用的金属陶瓷涂层的研发提供重要的科学依据。

热喷涂WC-Co硬质合金涂层在大型机械装备表面耐磨、耐蚀防护上具有不可替代的重要作用，然而在熔融锌等环境中Co相极易遭受腐蚀而导致涂层过早失效。本项目提出利用金属氧化物与碳的原位反应合成纳米WC和耐锌液腐蚀的Co-W-C化合物即η相以替代单质Co，建立了物相、成分和粒径可控的纳米WC-η复合粉末的制备技术，平均晶粒尺寸可降低至50nm。揭示了η相和Co在不同反应阶段促进W低温碳化生成WC的作用机理。阐明了喷涂颗粒致密性对纳米WC在高温喷涂焰流中脱碳的影响规律，据此发明了基于高熔点陶瓷颗粒的分隔辅助烧结制备全致密WC基球形粉末的创新技术，完全避免了WC在超音速火焰喷涂过程中的脱碳，同时在制备涂层中获得了一定量的纳米晶Co组织，阐明了喂料粉末全致密化对涂层耐磨性能的强化机理。基于优化工艺制备的低碳纳米结构WC-η喂料粉末和涂层，研究获得了Zn在WC-η复相涂层中的扩散规律及涂层失效原因。提出基于WC的微合金化及以三元WCoB化合物替代Co粘结相的改进策略，实现了制备的硬质合金涂层耐磨耐蚀性能的协同提高。基于本项目研究成果，发表了SCI收录论文10篇，EI收录论文1篇，其中影响因子大于5.0的论文3篇，影响因子3.0-5.0的论文5篇；获授权国家发明专利3项。