Ni基合金激光熔覆层组织特征及凝固过程的研究

Microstructure and Solidification Process of the Laser Clad Ni Alloy

采用自动送粉方法 ,在 45钢表面激光熔覆 Ni基合金粉末 ,较为系统地研究了扫描速度对激光熔覆层显微组织特征的影响。实验结果表明 :Ni基合金粉末激光熔覆层显微组织由枝晶及块状 (或针状 )共晶组织构成 ,共晶碳化物的形态由化学成分确定 ;结合界面不存在白亮带 ,为细小亚共晶组织 ;离结合界面距离的增加 ,熔覆层组织逐渐变细 ,显微组织表现出明显不均匀性 ;提高激光扫描速度 ,明显细化了组织 ,提高了组织显微硬度 ,改善了熔覆层局部组织不均匀性。结合激光熔覆解析模型 ,计算出激光熔池局部特征凝固参数 。

Laser cladding was done on the 45 # steel substrate using an auto feeding powder method. Effect of scanning speed on the microstructure and solidification process of the laser cladd Ni alloy have been systematically studied. Experimental results show that the clad microstructure is composed of primary dendrite and block(or needle) eutectic. The mophology of eutectic carbide is resulted from its chemical composition. Bright ribbon does not exist, and there is finer hypoeutectic microstructure at the interface between overlapping and clad layers. The clad microstructure becomes finer and inhomgeneous with increasing the distance from the interface. The increase of scanning speed results in finer structure, higher micro hardness, and better homogeneity. The solidification process is discussed based on the analyzed model. Some solidification parameters of laser melting bath are also calculated.