海水环境中Co基涂层的设计及腐蚀-气蚀耦合损伤机理研究

The main damage mode of key marine engineering equipment such as propellers and rudders is the coupling effect of corrosion-cavitation erosion, while their service performance can be effectively improved by preparing thermal spraying functional coatings on the surfaces. Aiming at the problem of insufficient understanding of the coupling damage mechanism of corrosion-cavitation erosion of these coatings in seawater, based on the fact found in our previous researches that the films formed by the interaction of cobalt with seawater can reduce the cavitation erosion degree of coatings, combined with the recent progress in the effect of oxidation resistance on cavitation erosion of materials, several special corrosion-cavitation erosion resistant Co-based coating materials used in marine environment are prepared in this application with considering appropriate seawater corrosion and high temperature oxidation resistance as key factors to further investigate the coupling damage mechanism of corrosion-cavitation erosion. After investigation of the corrosion properties of coatings in seawater, the phase composition and microstructures required for moderate corrosion are demonstrated through analyzing the filling effect of reaction films on pores as well as the promoting effect on the interfacial bonding of splats. Additionally, through comparative investigation on the cavitation erosion behaviors of coatings in freshwater and seawater conditions, the cavitation erosion damage mechanism of coatings caused by mechanical impact and instantaneous high temperature is deeply analyzed. Meanwhile, the inhibitory effect of reaction film on cavitation erosion and the influence of cavitation erosion on corrosion are emphatically analyzed, thereby elucidating the coupling damage mechanism and life extension mechanism of coatings. This application hopes to establish the design basis and theoretical foundation for special thermal sprayed corrosion-cavitation erosion resistant coating materials used in marine environment.

腐-气蚀耦合作用是导致海工装备螺旋桨和船舵等关键件失效的主要损伤模式，利用热喷涂技术在其表面制备功能涂层能够有效改善其使役性能。本项目针对目前对此类涂层在海水中腐-气蚀耦合损伤机理认识不足的问题，在前期研究发现钴与海水作用生成的反应膜可减轻涂层气蚀程度的基础上，结合抗氧化性影响材料气蚀性能的国内外最新研究进展，将适度海水腐蚀和耐高温氧化作为关键因素设计制备海洋专用耐腐-气蚀Co基涂层材料，深入研究其在海水中的腐-气蚀耦合损伤机理。通过研究涂层在海水中的腐蚀性能，分析反应膜对孔隙的填充作用和对扁平粒子间界面结合的促进作用，明确涂层发生适度腐蚀所需的物相结构。通过对比研究涂层在淡水和海水中的气蚀性能，剖析机械冲击和瞬间高温造成涂层损坏的气蚀机理；重点分析海水中反应膜对气蚀的抑制作用，及气蚀对腐蚀的影响，阐明涂层的耦合损伤机理和延寿机制。建立海洋专用热喷涂耐腐-气蚀涂层材料的设计依据及理论基础。

腐-气蚀耦合作用是导致海工装备螺旋桨和船舵等过流部件失效的主要损伤模式，利用热喷涂技术在其表面制备功能涂层能够有效改善其使役性能。但由于对材料在气蚀过程中发生的高温氧化、机械冲击和海水腐蚀之间的相互作用的认知并不清晰，导致无法有效指导设计制备抗腐-气蚀性能更好的涂层材料。在前期研究发现Co基涂层在海水中具有比在去离子水中更好的抗气蚀性能的基础上，本项目利用超音速火焰喷涂技术设计制备了不同物相组分和组织结构的Co基涂层，通过详细研究它们的力学、腐蚀和气蚀等性能，发现由于Co基涂层的耐高温氧化性能较好，空泡溃灭产生的瞬间高温仅能把涂层表面的Co和Cr元素氧化成纳米颗粒。而在气蚀条件下，材料的腐蚀机制发生变化，体现为海水腐蚀与瞬间高温一起协同腐蚀Co和Cr元素，促进更多的纳米氧化物颗粒在气蚀表面生成，更好地填充了涂层表面的缺陷并起到增强增韧作用，可有效减轻涂层的机械破坏。即Co基涂层在海水中发生气蚀时具有很好的“自修复”和“自增强”能力，这正是Co基涂层在海水中反而具有更好抗气蚀性能的原因，有效阐明了这类涂层的腐-气蚀耦合损坏机理和延寿机制。继而通过研究并揭示高温时效处理对涂层组织结构的调控规律，不仅在Co基涂层表面形成了致密的氧化膜，而且促进了涂层中扁平粒子间的融合，显著提升了涂层的致密度和内聚强度，同时在Co基合金的晶界处还析出了大量纳米碳化物增强相，进一步改善了其力学性能，最终显著延长了涂层的耐气蚀寿命，约为喷涂态涂层的23.8倍。在此基础上，又发展出真空浸渍聚合物和预热基材两种提升涂层致密度、内聚强度和力学性能的新型方案，丰富了热喷涂耐腐-气蚀涂层材料的设计依据及理论基础，为这类材料在海工装备过流部件表面的应用指明了方向。