TIG电弧堆焊条件下Ni基熔覆层的微观组织及性能研究

Microstructure and Properties of Ni-based Melting Layer by TIG Arc Welding

为了优化Q345低碳钢的表面使用性能,减少基材对Ni基熔覆层的稀释作用,设计了3组不同Fe含量的镍基金属粉芯焊丝,采用TIG沉积方法制备了3种过渡层+Inconel 625熔覆层,利用OM、SEM、EDS和显微硬度测试等方法,研究了熔覆层的微观组织、元素分布、物相组成、界面元素扩散和表面硬度等,为梯度Ni基熔覆层的推广应用提供一定的理论支撑。结果表明,在凝固温度的影响下,熔覆层由界面至顶部形成了不同的晶粒形貌。熔覆层主要由FCC结构的γ-Ni基体、Laves相和MC相组成,其中,由于微观偏析的存在,固溶体内元素分布不均匀,Ni、Cr、Fe元素主要富集在晶内,Mo、Nb在晶间聚集;随着Fe元素含量的增加,过渡熔覆层中元素偏析程度有所减缓,不规则形状的Laves相含量减少;得益于合金元素的固溶强化和第二相粒子强化作用,Inconel 625熔覆层平均硬度达到200 HV0.2以上,过渡层上部由于重复热输入影响,硬度值略低;熔覆层显微硬度均高于Q345基材。

In order to optimize the surface performance of Q345 low carbon steel and reduce the dilution effect of substrate on Ni-based fusion layer, three groups of nickel-based metal powder-cored wires with different Fe content were designed, and three kinds of transition layer+Inconel 625 fusion layer were prepared by TIG deposition method. The microstructure, element distribution, phase composition, interface element diffusion and surface hardness of the fusion layer were studied by OM, SEM, EDS and microhardness test, which provided theoretical support for the popularization and application of gradient Ni-based fusion layer. The results show that under the influence of solidification temperature, the melted coating layer forms different grain morphologies from the interface to the top. The coating is mainly composed of FCC structure γ-Ni matrix, Laves phase and MC phase. Due to the existence of microsegregation, the element distribution in the solid solution is not uniform, Ni, Cr and Fe are mainly enriched in the crystal, and Mo and Nb are gathered between the crystals. With the increase of Fe content, the degree of element segregation in the transition melting layer slows down, and the content of Laves phase with irregular shape decreases. Thanks to the solid solution strengthening and second-phase particle strengthening of alloy elements, the average hardness of Inconel 625 melted coating layer reaches above 200 HV0.2, and the hardness is slightly lower in the upper part of the transition layer due to the influence of repeated heat input. The microhardness of the fusion layer is higher than that of Q345 substrate.