Preparation Of Ni Coated Ultrafine WC Powders And Its Application In Wearable Coatings

Superfine WC powers can hardly be used in spray technology due to their poor liquidity. If nickel is used to coat some of them together, it will improve their liquidity greatly; this nickel coated structure will break down during the spray process because of the melting of nickel on the surface, causing WC particles to separate and at last form a coating with superfine WC dispersed in it.Nickel coated superfine WC powers was prepared by nonhomogenous precipitation using Ni(NO₃)₂·6H₂O, NH₄HCO₃ and superfine WC powers as start materials. Then it was mixed with Ni-based self-melting alloy to form coatings with dispersed distribution of superfine WC, and their performances of abrasive wear were studied.The effects of the dispersant type (PEG400, PEG2000, PEG6000 and sodium hexametahposphate), reagent concentration and mixed type of the precipitator on the coated power were studied. Experiment results indicated that the dispensability of superfine WC particles can be improved by using PEG2000 as dispersant and adding the dispersed WC in batch into lower concentration reagent. Slowly dripping the precipitator into the reagent suspension made it possible for nickel precursor precipitated on the surface of superfine WC particles rather then spontaneous nucleation.The superfme-WC-metal composite coating was prepared by flame spray method with good quality and fine bond strength; hardness and wear resistance of the coating could be increased by adding sub-micron WC; there were great influences on the coating using different disperse mode of superfine WC; coatings with dispersed distribution of superfine WC could be obtained by using PEG400, PEG2000 and absolute alcohol as dispersant and ball milling, and the wear resistance of the coating was improved. Great attention should be imposed on the particle size of WC since it had big influence on the wear resistance of the coating, coatings with the same volume fraction of both micron WC and sub-micron WC were prepared, and wear resistance of the latter is better than the former; better wear resistance could be obtained by mixing them together.A model was established account for abrasive wear in metal based particle...