摘要
汽轮机末级叶片在服役期间进汽边极易受汽蚀破坏,造成尺寸缺失,影响机组整体运行状况。为修复汽轮机叶片尺寸、提高其使用寿命,利用激光熔覆技术在17-4PH钢制备同材料熔覆层,并采用后热处理改善其组织,提高抗汽蚀性能。利用高温箱式炉对17-4PH熔覆层进行530、580以及630℃温度下的直接时效处理,使用OM、XRD、SEM以及配套的EBSD对组织进行表征分析,并通过超声波系统测试试样耐汽蚀性能。结果表明,经直接时效处理后熔覆层内部残余应力得到释放,组织内部奥氏体含量上升,且析出大量沉淀相。熔覆层汽蚀累积质量损失随时效温度上升呈现先上升后下降:经530℃处理后,试样汽蚀累积质量损失最低,仅为60.6 mg,相较于沉积态145.4 mg,质量损失减少了约58%。此外,汽蚀表面粗糙度在经时效处理后得到较好改善,其中在580℃试样中表现最佳,为180μm,表现出较好的抗汽蚀性能。通过对17-4PH熔覆层采用合适温度的直接时效处理,能够有效促进组织的均匀化,提高抗汽蚀性能,为汽轮机末级叶片的汽蚀损伤修复提供重要的工程指导。
inlet, which significantly affects the long-term performance of these turbines. Cavitation leads to the dimensional loss of the blades,resulting in reduced efficiency and, in extreme cases, mechanical failure of the unit. Cavitation is a phenomenon in which vapor bubbles form in low-pressure regions and collapse when moving into higher-pressure areas, causing localized shock waves that erode material surfaces. The inlet region of turbine blades is particularly vulnerable due to constant exposure to fluctuating pressures and high-velocity steam flow. To combat this issue and ensure the continued operation of steam turbines, repairing damaged turbine blades is an essential maintenance task. One promising approach to address cavitation damage involves restoring blade dimensions by means of laser cladding technology, which enables the deposition of a cladding layer onto the worn areas of the blades. In this study, a cladding layer composed of 17-4PH steel, the same material used in the original turbine blades, is fabricated on damaged blade surfaces using laser cladding. 17-4PH stainless steel, a martensitic precipitation-hardening material, is chosen because of its high strength, corrosion resistance, and ability to be age-hardened, making it suitable for turbine blade repair. The deposited cladding layer is then subjected to post-heat treatment, specifically direct aging treatments, to enhance the microstructure and improve its resistance to cavitation, which is critical to ensure the longevity of the repaired blades. The direct aging treatments are conducted at three temperatures: 530, 580, and 630 C, in a high-temperature box furnace. These temperatures are selected to investigate their effects on the mechanical properties and microstructure of the cladding layer. For a thorough analysis of the microstructural changes induced by the aging treatments, several advanced characterization techniques are employed, including optical microscopy, X-ray diffraction,scanning electron microscopy, and electron backscatter diffraction. Each technique provides complementary insights into the grain structure, phase composition, and distribution of precipitates in the aged cladding layer. In addition, the cavitation resistance of the treated specimens is evaluated using an ultrasonic testing system, which simulates the erosive effects of cavitation on the material surface by subjecting it to high-frequency vibrations in a liquid medium. The results of this study reveal that direct aging treatment plays a critical role in relieving internal residual stresses in the cladding layer, which are introduced during the laser cladding process.Moreover, it enhances the microstructural stability by increasing the content of retained austenite and promoting the precipitation of strengthening phases. These changes improve the material's ability to withstand the aggressive erosive action of cavitation.Interestingly, mass loss due to cavitation in the cladding layer exhibits a non-linear trend in terms of aging temperature. Specifically,the cumulative mass loss initially increases as the aging temperature increases but decreases after reaching a certain point. The lowest mass loss, measured at 60.6 mg, is observed in the specimen aged at 530 C, representing a substantial reduction of approximately 58% as compared with the as-deposited state, where mass loss was recorded at 145.4 mg. By contrast, the specimen aged at 630experiences relatively higher mass loss, suggesting that excessively high aging temperatures may not be beneficial for cavitation resistance. Surface roughness, another crucial indicator of cavitation resistance, is also significantly improved after aging. The optimal surface roughness of 180 µm is observed in the specimen treated at 580 C, indicating superior resistance to cavitation damage. These findings suggest that selecting a suitable aging temperature is critical for achieving a balance between improving the mechanical properties and cavitation resistance of the cladding layer. Therefore, applying suitable direct aging temperatures to the 17-4PH cladding layer promotes homogenization of the microstructure and enhances the material's resistance to cavitation. This provides a potent strategy for extending the life and maintaining the integrity of turbine blades, offering important engineering guidance for the repair and restoration of cavitation-damaged turbine blades.
作者
董刚
胡健东
王永强
李国明
姜晓峰
张群莉
姚建华
DONG Gang;HU Jiandong;WANG Yongqiang;LI Guoming;JIANG Xiaofeng;ZHANG Qunli;YAO Jianhua(Institute of Laser Advanced Manufacturing,Zhejiang University of Technology,Hangzhou 310023,China;Key laboratory of Special Purpose Equipment and Advanced Processing Technology of Ministry of Education/Zhejiang Provincial,Zhejiang University of Technology,Hangzhou 310023,China;School of Mechanical Engineering,Zhejiang University of Technology,Hangzhou 310023,China;Maintenance Department,State Power Zhejiang Beilun 1st Generating Co.,Ltd.,Ningbo 315800,China)
出处
《中国表面工程》
北大核心
2025年第6期124-134,共11页
China Surface Engineering
基金
国家重点研发计划项目(2023YFB4603400)
国家自然科学基金重点项目(52035014)
浙江省“尖兵”攻关计划项目(2022C03021)。
