以FCo-5自熔性钴基合金粉末为堆焊材料，在0Cr18Ni12Mo3Ti核阀试样表面制备厚度为2.04 mm、横截面单圆弧拟合半径为2.69 mm的密封面激光熔覆层。利用SEM和XRD分析熔覆层的微观结构和物相，测试熔覆层的显微硬度及最小厚度处的高温硬度。结果表明：熔覆层从界面到表层的结晶形态依次由平面晶向胞状树枝晶、多方向生长树枝晶、细小树枝晶过渡；中、上部组织主要由γ-Co 奥氏体枝晶、枝晶间层片状共晶组织以及弥散分布的Cr23C6硬质颗粒组成；在距界面1.52~1.60 mm的区域，密封带宽度为2.95～3.18 mm，常温硬度阈值为44.3～45 HRC；在650℃以下时，熔覆层最小厚度处具有优异的抗蠕变性能和高温硬度特性，经720℃以上回火处理后有较强的二次硬化效应。%A sealing surface laser cladding layer with thickness of 2.04 mm and cross section of circular arc having a fitting radius of 2.69 mm was prepared on a 0Cr18Ni12Mo3Ti nuclear valve sample surface using FCo-5 fluxed cobalt-base alloy powder as overlaying welding material. The microstructure and phase composition of the cladding layer were analyzed using SEM and XRD. The microhardness of the cladding layer and high temperature hardness at the position with minimum thickness were measured. The results show that the crystal morphology of coating altered in turn as plane crystal cellular dendrites, multi-directional growth dendrites and fine dendrites from the interface to surface. The mid and upper microstructure mainly consists of γ-Co austenite dendrite, interdendritic layer lamellar eutectic organization and dispersed Cr23C6 hard particle phase. The seal belt width varies from 2.95 mm to 3.18 mm, hardness threshold under normal temperature is 44.3~45 HRC in the region away from the interface 1.52~1.60 mm. The minimum thickness localized cladding layer has the characteristic of good creep resistance and high temperature hardness below 650℃, as well as can generate strong secondary hardening effect after tempering above 720℃.
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