【摘要】 目的提升激光熔覆Ni基涂层表面组织及耐蚀性能。方法采用激光熔覆技术制备成形好、无裂纹的Ni基涂层,随后进行超声冲击处理。采用扫描电子显微镜(SEM)、电子探针(EPMA)及电化学设备等,研究熔覆层和冲击硬化层的组织及耐蚀性能,分析Ni基熔覆层的冲击强化机制。结果激光熔覆Ni基涂层主要由γ-(Fe,Ni)固溶体和晶界碳化物组成,组织形貌由底及表为胞状树枝晶和细小的树枝晶。熔覆层内晶界的Cr元素含量高于晶内,且上部枝晶内的Cr元素含量高于底部和中部。超声冲击处理未改变熔覆层内的物相组成,但在表面形成厚度约5μm的细晶层,冲击硬化层内晶界的碳化物被破碎成细小的碳化物并弥散分布于晶内,起到细晶强化和弥散强化的作用。超声冲击后,表面粗糙度由0.52μm降至0.29μm,硬度提升50%以上。电化学测试表明,冲击硬化层的平均自腐蚀电位上升37.21mV,平均自腐蚀电流密度下降57.9%,腐蚀表面均匀平整,大量细小的碳化物弥散分布。结论超声冲击处理细化了Ni基熔覆层的表层组织,且表面的耐蚀性能明显提高。更多还原

【Abstract】 To improve the microstructures and corrosion resistance of Ni-based cladding coatings, the crack free Ni-based coatings were prepared by laser cladding technology, and then were treated by ultrasonic impact. The microstructure and corrosion resistance of cladding coating and impact hardening layer were studied by scanning electron microscope(SEM),electron probe microanalysis(EPMA) and electrochemical equipment, and the hardening mechanism of Ni-based cladding coating by ultrasonic impact treatment was analyzed. The results show that the laser cladding Ni-based coating was mainly composed of γ-(Fe,Ni) solid solution and carbides along grain boundary. The microstructure of laser cladding Ni-based coating was composed of cellular dendrite and fine dendrite from the bottom to top region. In addition, the Cr content at the grain boundaries in cladding coating was higher than that at grain boundaries while the Cr content intragranular at upper region was higher than at the bottom and middle regions. Ultrasonic impact treatment does not change the phase composition of Ni-based cladding coating, but on the surface of which a fine grain layer with a thickness of 5 μm was formed. The carbides distributed along the grain boundaries in the impact hardening layer were broken into fine carbides and dispersed inside the grains, which played the role of fine grain strengthening and dispersion strengthening. After ultrasonic impact treatment, the surface roughness decreased from 0.52 μm to 0.29 μm, and the surface hardness increased by more than 50%. The general self-corrosion potential of impact hardened layer increased by 37.21 mV, and the general self-corrosion current density decreased by 57.9%, while the corrosion surface was even and smooth with many fine carbides dispersed. Therefore, ultrasonic impact treatment could refine the microstructures of laser cladding Ni-based coating, and the corrosion resistance of which was improved obviously.更多还原