强流脉冲离子束辐照核级硬质合金涂层复相协同冲击应变机制研究

Substituting Ni for radioactive Co as binder phase in WC based cemented carbide thermal sprayed coatings is promising for wear- and corrosion- resistant applications in key components of nuclear coolant pump in nuclear power plants, such as shafts, bearings and mechanical seals. However, Ni cemented carbide coatings possess lower strength and hardness in comparison with the Co counterparts. Effective strengthening of WC-Ni cemented carbide coatings are indispensable for high reliabile and safe long term run of the equipments in nuclear power plants. Laser and elecltron beams technonlogies of remelting principle, currently available for strengthening of thermal spary coatings, are still not sufficient for the cemented carbide coatings applications due to formation of penetrating cracks or brittle phases, as a result of thermal stress and chemical reaction induced by notable thermal effect across the entire coating up to a few hundreds micrometers. In this project, a high-intensity pulsed ion beam approach is proposed to improve the overall properties of nuclear grade WC-Ni coatings, based on unconfined shock strengthening principle instead of deep remelting of the coatings. The shock processing is to be investigated concerning the non-equilbrium coupled thermal-dynamical effects (involving ultra-fast heating, remelting and ablation in the ion-implanted top layer within a few micrometers) and thus produced strong shock stress waves propogating inwards. The coupled formation of a thin top remelted layer and a deep shock deformation layer down to a few hundreds micrometers will be clarified through characterizations of shock deformed microstructures and resultant wear, corrosion and fatigue properties. Synergetic shock deformation behavior of the biphase structure in the coatings, i.e. WC hard phase and Ni binder, will be particularly studied in addition to its effect for improving the coatings' wear, corrosion, and fatigue resistance, to develop a new and reliable apprach to improving the overall properties of WC based cemented carbide coatings, extending their applications in the equipments in nuclear power plants.

以Ni替代产生放射性的Co做粘结相的无钴WC基硬质合金热喷涂涂层，在核主泵泵轴、轴承及密封等关键部件耐磨抗蚀应用，但无钴化涂层强度硬度有所降低，亟待发展有效的涂层强化技术以满足核电装备高可靠、长寿命安全运行要求。目前基于重熔改性的激光和电子束等工艺因深层熔化易形成贯穿热裂纹及大量脆性相，涂层强化效果有限。本项目拟采用自主研发的大面积强流脉冲离子束表面工程技术，辐照无钴WC基硬质合金热喷涂涂层，研究辐照非平衡热-力耦合无约束冲击作用（离子射程区快速加热、熔化与烧蚀，及由此产生向内传播的冲击应力波），通过对辐照涂层的材料学分析、磨损腐蚀及疲劳行为研究，掌握低应力重熔浅表层和深达数百微米冲击应变层的耦合形成规律，探明辐照涂层的WC硬质相/金属粘结相复相结构的协同冲击应变机制及其对性能改善作用，发展出核级硬质合金涂层耐磨抗蚀抗疲劳复合强化新技术，为有效提升涂层性能、拓展其在核电装备中应用创造条件。

与传统的WC-Co系硬质合金相比较，WC-Ni系硬质合金在核主泵泵轴、轴承及密封等关键部件具有明显的抗腐蚀和抗辐照的优势，但耐磨性能偏低。基于激光和电子束熔凝原理的涂层重熔改性工艺，存在贯穿热裂纹及大量脆性相等技术瓶颈，改善效果有限。本项目采用自主研发的大面积强流脉冲碳离子束技术，开展了强流脉冲离子束辐照WC-Ni系硬质合金非平衡热—力耦合无约束冲击作用实验与数值模拟研究，探明了100 ns短脉冲、射程小于1 μm强流碳离子注入，转化为冲击热应力作用，在硬质合金辐照改性表面形成了微米近表层重熔致密化和百微米深层冲击强化的复合改性组织，特别是结合预加热方法对热-力耦合效应的调控表面拉应力形成条件，抑制了改性表面的微裂纹，不仅摩擦系数降低，而且耐磨性能显著提升，从原始硬质合金的磨粒磨损行为，转变为整体微磨削和粘着磨损机制。开发出稳定输出的碳离子束源，保证了核级硬质合金及其涂层表面强化新技术，已在我国自主研制的核主泵试验件制造中取得初步应用。