超细结构WC-η涂层的制备及其耐熔锌腐蚀性能

Fabrication of ultrafine-structured WC-η coating and its corrosion resistance to molten zinc

摘要:

以钨氧化物、钴氧化物和炭黑为原料,采用创新的原位反应技术快速合成超细WC-η复合粉,在优化的工艺条件下制备复合粉中只含有WC和Co₆W₆C相,粉末平均粒径为260nm。复合粉经团聚造粒制备得到具有高致密性和良好流动性的热喷涂粉末,以此粉末作为喂料利用超音速火焰喷涂技术制备得到超细结构的WC基涂层,其平均显微硬度达到(1406±34)HV_0.3,孔隙率仅为0.3%。熔融锌腐蚀结果表明,制备的超细结构WC基涂层具有良好的耐熔锌腐蚀性能,其腐蚀机制主要是锌液沿微裂纹扩散导致涂层自表层向内部出现缓慢的溶解腐蚀,并逐渐形成贯穿性裂纹而引起涂层材料的大块剥落。

Abstract:

Using tungsten oxide, cobalt oxide and carbon black as raw materials, the ultrafine WC-η composite powder was rapidly synthesized by the novel technique of in situ reactions. Under the optimized process conditions, the as-synthesized composite powder has a mean particle size of 260 nm, containing only WC and η phases. Then the composite powder was agglomerated into the thermal spray powder with high density and good flowability. Using this powder as the feedstock, the ultrafine-structured WC-based coating was fabricated by high-velocity oxy-fuel spraying technique. The fabricated coating has an average hardness as high as (1406±34) HV_0.3 and only a porosity of 0.3%. The results indicated that the ultrafine-structured WC-based coating exhibited excellent corrosion resistance to molten zinc. The corrosion mechanism can be explained by the slow dissolving of the coating matrix from the surface layer to the inner area caused by the diffusion of molten zinc along micro-cracks, which was then followed by the formation of penetrative cracks and subsequent massive exfoliation of coating materials.