Study On Preparation And Properties Of WC/Co-based Thermal Spray Powder And Coating

Thermal spraying is an emerging and important area of current scientificresearch technology to prepare tungsten carbide/cobalt based metal ceramic coating.The conventionnal spray technologies include:arc spraying, plasma spraying,detonation gun spraying and high velocity oxygen fuel (HVOF) spray. NowdaysHVOF is considered best and most widely used technology for thermal spraytungsten carbide/cobalt based metal ceramic with combination of excellent adhesionand wear resistance.In this paper the WC-10Co4Cr compound powder was prepared by means ofsintered-crushed method with micron WC,Co and Cr3C2powder as raw materials.The addition of Cr3C2, sintering time for the preparation of WC-10Co4Cr compositepowder were investigated, structuer and performance of the sintered powder werecharacterized. Two kinds of WC-12Co and WC-10Co4Cr wear-resistant coating weresprayed using HVOF technology.The powder composition,structure,the use of liquidfuel for coating structure, anti-corrosion and sliding wear resistance of theWC-10Co4Cr coating were studied.The conclusions are listed as following:The WC-10Co4Cr composite powder is prepared with1.5μmWC,1.5μm Co andCr3C2powder by mechanical milling and sintered-crushered method. After sinteredfor1.5h-5h in1250℃hydrogen atmosphere,the powder morphology and phasecomposition change significantly.After sintered for1.5h, the powder consists of themain phase WC and Cr3C2phase, together with small amount of Co3W3C and Cr7C3phase;after2.5h of sintering the Cr3C2phase disappears, indicating that completediffusion of Cr3C2, the WC grain size does not grow significantly; after5h ofsintering, massive decarburized η phase (Co3W3C, and Co6W6C), or even metallic Wphase emerge,together with some oxidation phase of WO3, WO2and Cr2O3phase.Also, the WC grain grows.Two kinds of dense coating were sprayed with JP-5000gun. The WC-10Co4Crcoating has porosity of0.8%and average microhardness of HV0.31322while theWC-12Co coating has porosity of1.1%and average microhardness of HV0.31238.5.The main phase of WC-10Co4Cr and WC-12Co prepared with the same sprayingparameters is WC phase with low decarburization degree. For the WC-10Co4Crcoating there are a small amount of new phase W2C without η phase (Co3W3C, Co6W6C); while for the WC-12Co coating there are a small amount of new phasesW2C and trace phase of Co6W6C.The volume wear ratio of the WC-10Co4Cr coating is1/146that of the stainlesssteel(1Cr18Ni9Ti) meterial. The friction coefficient after1000s stabilizes at about0.8under the conditions of load10N, speed600r/min and wear time120min. Thesliding wear mechanism is fragmentation of WC and three-body abrasive wear. Theneutral salt spray corrosion test and electrochemical polarization were conducted in3.5%NaCl solution at25±0.5°C, with potentiodynamic scanning speed0.001V/s,scanning potential range for Eocp in-300~+200mV. The WC-10Co4Cr coatingshows excellent,the corrosion resistance decreases with the order corrosion-resistantperformance WC-10Co4Cr coating>the hard chrome plating>stainless steel(1Cr18Ni9Ti).