Cavitation erosion is a sever wear mechanism that takes place in hydrodynamic systems. Examples are turbine vanes of hydropower plants or components of valves and pumps in hydraulic systems. Nickel-titanium shape memory alloys (NiTi) are attractive materials for cavitation-resistant coatings because of their pronounced intrinsic damping mitigating cavitation-induced erosion. In this work, NiTi coatings were produced by cold gas spraying. The phase transformation behaviors of the powder feedstock and the as-sprayed coatings were investigated. Regarding the obtained transformation temperatures, the measured substrate temperatures during spraying rule out that either the shape memory effect or the pseudoelasticity of NiTi could affect the deposition efficiency under the applied conditions of cold gas spraying. Another potential effect is stress-induced amorphization which could occur at the particle–substrate interfaces and impair particle bonding by stress relaxation. Moreover, also oxide formation can be significant. Thus, the presence of amorphous phases and oxides in the near-surface zone of particles bounced off after impact was investigated. Oxidation could be confirmed, but no indication of amorphous phase was found. Besides, also the evolution of local microstrains implies that the substrate temperatures affect the deposition efficiency. These temperatures were significantly influenced by the spray gun travel speed.

中文翻译：

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镍钛涂层的冷气喷涂可防止气蚀


空蚀是发生在流体动力系统中的一种严重磨损机制。例如水力发电厂的涡轮叶片或液压系统中的阀门和泵组件。镍钛形状记忆合金（NiTi）是抗空化涂层的有吸引力的材料，因为它们具有明显的固有阻尼，可以减轻空化引起的侵蚀。在这项工作中，镍钛涂层是通过冷气体喷涂生产的。研究了粉末原料和喷涂涂层的相变行为。关于获得的转变温度，喷涂过程中测量的基体温度排除了镍钛的形状记忆效应或伪弹性可能影响冷气喷涂条件下的沉积效率。另一个潜在的影响是应力引起的非晶化，它可能发生在颗粒-基底界面处，并通过应力松弛损害颗粒结合。此外，氧化物的形成也可能很严重。因此，研究了冲击后反弹的颗粒近表面区域中非晶相和氧化物的存在。可以确认氧化，但没有发现非晶相的迹象。此外，局部微应变的演变也意味着基底温度会影响沉积效率。这些温度受喷枪行进速度的显着影响。