Electroless Nickel Plating On WC-10Ni Powders And Its Effect On Deposition And Phase Structures Of HVOF Coating

In this paper,electroless plating was used to coat the WC-10Ni powder.At the same time,the deposition rate,the degree of WC decarburization and the phase structure of the corresponding HVOF cemented carbide coatings were studied.The purpose of this paper is to improve the oxidation and decarburization of WC-Ni cemented carbide powder in supersonic flame spraying and to improve the wettability between the hard phase and the metal matrix,so as to improve coating properties for application in aerospace,petrochemical,mining and nuclear fields.The influence and mechanism of different pretreatment processes during electroless Ni-deposition on the surface of low I.E.P powders are studied,and a direct simplified electroless plating method is proposed.The influence of mechanical stirring speed and Ni salt type on the thickness uniformity and coating integrity of the Ni-layers were discussed and differential thermal analysis was used to evaluate the thermal stability of Ni-coated WC-10Ni powders at high temperatures.Ni-coated WC-10Ni powders were made into coatings through HVOF.The phase structure of the coatings was analyzed by XRD and EPMA,and the effect of Ni-coating on the structure of HVOF coating during deposition was discussed.It is found that,in addition to the pretreatment of Sn Cl₂-Pd Cl₂ in the traditional electroless plating process,electroless Ni-plating can also be carried out on the low I.E.P powder surface with activation only by Pd Cl₂ and direct deposition of Ni.Continuous and uniform Ni coatings on WC-10Ni cemented carbide powders can be prepared by using nickel chloride as nickel salt compared with that by nickel acetate at the mechanical mixing speed of 1400 r/min.In HVOF process of the coatings,the powder feeding rate and deposition thickness of Ni-coated WC-10Ni powder are lower than that of the raw powders,but the densification behavior of the sprayed coating is improved.At the same time,compared with the sprayed coatings prepared with raw Wc-10Ni powder,the content of decarburized phase and porosity of the coatings prepared with Ni-coated powders are reduced,and the content of decarburized phase is reduced from the highest 2.45%to 0.3%,even to the lowest 0.1%.