中文摘要：

研究了送粉激光熔覆铁基合金添加Nb粉的可能性，并对熔覆试样进行了显微组织分析和硬度、磨损性能测试。扫描电镜、光学显微镜、能谱分析和X射线衍射分析结果表明，Nb在熔覆层中均匀分布，Nb的加入使枝晶组织明显细化，界面上方等轴晶数量增多，共晶组织更加致密。硬度测试和磨损试验表明，Nb元素的加入提高了熔覆层的显微硬度、耐磨性。分析认为，组织与性能的提高是由于Nb的加入生成大量弥散均匀分布的NbC颗粒增强相，同时生成的NbC成为异质核，提高了凝固结晶过程中的形核率，并且Nb原子优先占据晶界，强化了晶界，阻碍了晶体的长大。

英文摘要：

The possibility of adding Nb to the powder feeding laser structure, hardness and wear resistance of the laser clad layer were tronmicroscopy （ SEM）, energy-dispersive spectrometer（EDS） and cladding Fe-based alloy was investigated. The microexamined. Optical microscopy （OM） , scanning elec- X-ray diffraction （XRD） results show that Nb atoms distribute homogenously in clad layer . With the addition of Nb, the dendrite crystals in the coating are obviously refined. The equiaxed grains on the interface increase and the eutecticum became denser. The addition of Nb in the cladding powder also resultes in increased hardness and improved wear resistance of the composite coating. It is considered that the improvement of the microstructure and properties is due to the formation of substantive NbC particles distributing homogenously in the coatings, and the particles of NbC act as inhomogenous crystalline nuclei that increased the nuclear rate during solidification. Nb atoms located preferentially in the crystal boundary enhance intercrystalline cohesion and suppresse the growth of the crystals.