45钢表面Ni/WC复合熔覆层的形成机制

Formation Mechanism of Ni/WC Composite Coatings on Carbon Steel

采用真空熔覆技术在45钢表面制备Ni+WC复合熔覆层并进行阶段性取样,研究镍基复合涂层的形成机制。结果表明:在45钢表面生成与基体冶金熔合、WC硬质颗粒分布均匀的Ni基复合熔覆层。整个熔覆层由4 mm厚的复合层、1 mm厚的过渡层、20μm厚的扩散熔合区以及250μm厚的扩散影响区组成。复合层区由WC和分解形成的富W复相碳化物包围在Ni颗粒周围组成;复合熔覆层的主要组成相有γ-Ni固溶体、Cr_7C_3、Ni_(2.9)Cr_(0.7)Fe_(0.36)、Cr_(23)C_6、Ni_3Fe、Ni3_Si、Ni_3B、W_2C以及C等;真空熔覆过程包括:镍基合金颗粒达到熔点(900℃)前升温阶段颗粒间微烧结颈的形成、升温达到熔点(1020℃)开始的镍基合金颗粒熔融以及保温阶段(1060℃)的熔合扩散与WC颗粒微区位置的调整。

Ni+WC composite cladding was prepared on the surface of 45#steel by vacuum cladding technology. The formation mechanism of nickel-based composite coating was investigated by intermittently sampling. The results show that a Ni-based composite cladding with metallurgical fusion to the matrix and uniform distribution of WC hard particles is obtained on the surface of 45 steel. The entire cladding consists of a 4 mm thick composite layer, a 1 mm thick transition layer, a 20 μm thick diffusion fused zone, and a 250 μm thick diffusion affected zone. The composite layer composes of WC and W-rich multiphase carbide formed after decomposition, surrounded by Ni particles;The main phase constituents of the composite cladding layer include γ-Ni solid solution, Cr7 C3, Ni2.9 Cr0.7 Fe0.36, Cr23 C6, Ni3 Fe, Ni3 Si, Ni3 B,W2 C and C. The vacuum cladding process mainly includes the formation of a micro-sintered neck between the particles in the heating stage before the Ni-based alloy particles reach its melting point, and the melting of the Ni-based alloy particles at the beginning stage of its melting point and the third stages of fusion diffusion in the heat preservation stage and position adjustment of the WC particle within micro-area.