钎焊温度对柔性镍基碳化钨金属布真空钎焊涂层组织及性能的影响

Effect of different brazing temperatures on Ni-based tungsten carbide coatings prepared by vacuum brazing using flexible metal cloth as brazing filler metal

摘要:

将由WC粉末、NiCrBSi粉末和粘结剂构成的混合金属粉末制备成柔性镍基碳化钨金属布,借助真空钎焊在Q235钢表面制备镍基碳化钨涂层。这种柔性金属布可以任意裁剪、任意折叠,实现了一些曲面异形结构件表面厚度可控涂层的制备。本文探讨了不同钎焊温度对镍基碳化钨涂层组织、界面结合强度、硬度和耐磨性的影响。结果表明：钎焊温度的升高不改变涂层微观组织构成,镍基碳化钨涂层/钢基体界面处主要由Fe的固溶体、Ni₃Si和Ni₃B构成,钎缝区主要是Ni的固溶体、WC、W₂C、CrB和Cr₇C₃等化合物构成。随着钎焊温度的升高,镍基碳化钨涂层的孔隙率和孔隙平均面积逐渐降低,涂层的致密度逐渐提高,从而涂层的硬度和耐磨性逐渐增加,这主要是因为柔性碳化钨金属布熔化后,随着钎焊温度的增加,熔融NiCrBSi金属对WC颗粒的包裹性和填充WC颗粒之间间隙的能力增强,减少了涂层中孔隙,提高了涂层的致密度,涂层具有较高的硬度和耐磨性。而镍基碳化钨涂层/钢基体结合强度随着钎焊温度的升高先增加后减小,当钎焊温度为1080℃时,涂层抗剪切强度最大,为336.5MPa。这是因为随着钎焊温度升高至1080℃,涂层/基体界面化合物层厚度从4.7μm增加至9.2μm,适合厚度的化合物增加了涂层与基体之间的结合强度。但钎焊温度进一步升高至1140℃,界面化合物层厚度增加至13.9μm,过厚的化合物层导致涂层抗剪切强度降低。

Abstract:

A flexible Ni-based tungsten carbide metal cloth, which prepared by mixing WC powder, NiCrBSi powder and the binder, was coated on the surface of Q235 steel by vacuum brazing. It enables the repair of internal and curved surfaces of components. The effect of different brazing temperatures on the microstructure, shear strength, microhardness and wear resistance of coatings were explored. The results showed that the increasing brazing temperature did not change the microstructure composition of the coating. The interface of Ni-based tungsten carbide coating and steel substrate was mainly composed of Fe solid solution, Ni₃B, Ni₃Si compounds while the brazing seam zone was mainly composed of Ni solid solution, WC, W₂C, CrB and Cr₇C₃ compounds. With the increasing of the brazing temperature, the porosity rate and its average area of the coating gradually decreased, finally the microhardness and wear resistance of the coating enhanced. It was mainly attributed to the fact that after the flexible Ni-based tungsten carbide metal cloth melting, the NiCrBSi molten liquid improved the wetting of WC particles and filled the gap among WC particles with the increase of brazing temperature, and the coating had quite high microhardness and wear resistance. The bonding strength between Ni-based tungsten carbide coating and steel substrate increased first and then decreased with the increase of brazing temperature. When the brazing temperature was 1080 ℃, the bonding strength of the coating was the maximum of 336.5MPa. It was because the thickness of the coating/steel substrate interface compounds layer increased from 4.7 μm to 9.2 μm when the brazing temperature increased 1080℃, and the compound layer with appropriate thickness increased the bonding strength between the coating and the substrate. However, the thickness of the interface compounds layer increased to 13.9 μm when the brazing temperature increased to 1140℃, and the compounds layer with the excessive thickness led to a decrease in the bonding strength of the coating.