Krella Alicja Krystyna
Institute of Fluid Flow Machinery PAS, Fiszera 14, 80-231 Gdańsk, Poland.
Materials (Basel). 2023 Mar 2;16(5):2058. doi: 10.3390/ma16052058.
The phenomena of cavitation and cavitation erosion affect hydraulic machines, increasing their maintenance costs. Both these phenomena and also the methods of preventing the destruction of materials are presented. The compressive stress in the surface layer created from the implosion of cavitation bubbles depends on the aggressiveness of the cavitation, which in turn depends on the test device and test conditions, and also affects the erosion rate. Comparing the erosion rates of different materials tested using different tests devices, the correlation with material hardness was confirmed. However, no one simple correlation was obtained but rather several were achieved. This indicates that in addition to hardness, cavitation erosion resistance is also affected by other properties, such as ductility, fatigue strength and fracture toughness. Various methods such as plasma nitriding, shot peening, deep rolling and coating deposition used to increase resistance to cavitation erosion by increasing the hardness of the material surface are presented. It is shown that the improvement depends on the substrate, coating material and test conditions, but even using the same materials and test conditions large differences in the improvement can be sometimes gained. Moreover, sometimes a slight change in the manufacturing conditions of the protective layer or coating component can even contribute to a deterioration in resistance compared with the untreated material. Plasma nitriding can improve resistance by even 20 times, but in most cases, the improvement was about two-fold. Shot peening or friction stir processing can improve erosion resistance up to five times. However, such treatment introduces compressive stresses into the surface layer, which reduces corrosion resistance. Testing in a 3.5% NaCl solution showed a deterioration of resistance. Other effective treatments were laser treatment (an improvement from 1.15 times to about 7 times), the deposition of PVD coatings (an improvement of up to 40 times) and HVOF coatings or HVAF coatings (an improvement of up to 6.5 times). It is shown that the ratio of the coating hardness to the hardness of the substrate is also very important, and for a value greater than the threshold value, the improvement in resistance decreases. A thick, hard and brittle coating or alloyed layer may impair the resistance compared to the untreated substrate material.
空化及空蚀现象会影响水力机械，增加其维护成本。文中介绍了这两种现象以及防止材料破坏的方法。空化气泡内爆在表面层产生的压应力取决于空化的侵蚀性，而空化侵蚀性又取决于测试装置和测试条件，同时也会影响侵蚀速率。比较使用不同测试装置对不同材料进行测试得到的侵蚀速率，证实了其与材料硬度的相关性。然而，并未得到单一的简单相关性，而是得到了多个相关性。这表明除硬度外，抗空蚀性还受其他性能影响，如延展性、疲劳强度和断裂韧性。文中介绍了各种通过提高材料表面硬度来增强抗空蚀性的方法，如等离子渗氮、喷丸处理、深层滚压和涂层沉积。结果表明，改进效果取决于基体、涂层材料和测试条件，但即使使用相同材料和测试条件，有时改进效果也会有很大差异。此外，有时保护层或涂层部件制造条件的微小变化甚至会导致与未处理材料相比抗蚀性下降。等离子渗氮可使抗蚀性提高20倍，但在大多数情况下，提高幅度约为两倍。喷丸处理或搅拌摩擦加工可使抗蚀性提高至五倍。然而，这种处理会在表面层引入压应力，从而降低耐腐蚀性。在3.5%氯化钠溶液中的测试表明抗蚀性下降。其他有效处理方法包括激光处理（提高1.15倍至约7倍）、物理气相沉积（PVD）涂层沉积（提高达40倍）以及高速氧燃料（HVOF）涂层或高速空气燃料（HVAF）涂层（提高达6.5倍）。结果表明，涂层硬度与基体硬度之比也非常重要，当该比值大于阈值时，抗蚀性的提高会降低。与未处理的基体材料相比，厚的、硬的且脆的涂层或合金层可能会削弱抗蚀性。
