基于水射流强化的钛镍涂层空化下马氏体再取向及其耐空蚀机制

Strengthened titanium-nickel coating cladding on ship fluid power components will be weaken during cavitation due to the formation of stable martensite and residual tensile stress. The project proposes that the titanium-nickel coating will be strengthened by peening using water jet. And this method is benefical to promote to generate orientation martensite and improve the cavitation erosion resistance. Dislocation movement and micro plastic deformation are studied during peening titanium-nickel coating by water jet. In addition, the mechanism of prefabricating residual compressive stress and inducing organization refinement will be revealed. Moreover, the phase transition behavior will be studied during cavitation. Dynamic evolution of the martensite will be analyzed and the condition of reversible phase transition will be proposed. Besides, the coupling relations between strengthened of mother phase, reorientation of martensitic variants, and orientation martensite, and the mechanism of fine crystal and residual compressive stress field will be clarified under cavitation. The cavitation erosion and failure behavior will be studied during cavitation. The relationships between water jet impact, fine grain and residual compressive stress field, martensite and residual stress, and cavitation and failure behavior will be established. The mechanism of extending the cavitation incubation period, containing cavitation crack initiation and propagation by strengthening the strain recovery under cavitation will be revealed. The expected results will enrich and develop the phase transition theory of titanium-nickel coatings during cavitation, and lay a theoretical foundation for the engineering application of titanium-nickel coating ship fluid power components.

针对舰船流体动力部件表面熔覆钛镍涂层空化下易形成稳定马氏体和产生残余拉应力降低抗空蚀效果的问题，项目提出采用水射流冲击方法强化钛镍涂层母相，诱发空化下形成取向马氏体以提高抗空蚀能力。研究水射流冲击钛镍涂层过程中位错运动和微观塑性变形特性，揭示诱导表层组织细化和预制残余压应力作用机制；研究空化工况下的相变行为，分析马氏体动态演变过程和提出相变可逆性条件，建立“母相强化-马氏体变体再取向-取向马氏体”之间的相互耦合关系，探讨细晶和残余压应力场在空化诱发相变中的作用机理；研究空化工况下的空蚀、失效行为，构建“水射流冲击-细晶和残余压应力场-马氏体和残余应力-空蚀和失效行为”之间关系模型，探明水射流冲击钛镍涂层加强空化下应变恢复以延长空蚀孕育期、遏制空蚀裂纹萌生和扩展作用机制。预期成果将丰富和发展钛镍涂层在空化工况下的相变理论，为实现钛镍涂层舰船流体动力部件的工程应用奠定理论基础。

采用符合ASTMG134国际标准的水射流设备，对钛镍合金的空蚀行为和抗空蚀机理进行了研究。研究水射流冲击钛镍合金过程中位错运动和微观塑性变形特性，揭示诱导表层组织细化和预制残余压应力作用机制；射流冲击下钛镍合金的累积质量损失率在180min内变化缓慢，240min后急剧上升并明显下降。当冲击时间从30min延长到60min时，试样表面的宏观变形并没有明显增加。这主要是由于钛镍合金的超弹性，导致钛镍合金在水射流作用下的空化潜伏期延长。冲击时间为180min时，试样在塑性变形的同时发生了加工硬化，表面出现了空蚀坑。当冲击时间从240min延长到300min时，空蚀坑和材料剥落均没有明显增加。这主要是由于在水射流冲击的表面及远离表面的晶界处，通过位错的堆积和重排形成了新的晶粒。新晶粒的形成消耗了高密度位错和畸变能量，可以减少水射流冲击对钛镍合金造成的空蚀损伤。随着水射流冲击时间的增加，钛镍合金表面经历了塑性变形→加工硬化→位错密度增大→晶粒细化→细晶粒增殖的过程。不同冲击时间的钛镍合金的残余应力均较高，能够抑制空化裂纹的萌生和扩展。构建了“水射流冲击-细晶和残余压应力场-相组成和残余应力-空蚀和失效行为”之间关系模型，探明水射流冲击钛镍加强空化下组织细化以延长空蚀孕育期、遏制空蚀裂纹萌生和扩展作用机制。丰富和发展钛镍在空化工况下的组织演变及变形理论，为实现钛镍舰船流体动力部件的工程应用奠定理论基础。