Influence Of WC-12Co Powder's Structure Characteristic On Its HVOF Coatings' Anti-cavitation Properties

Cavitation erosion is an important topic in hydrodynamics,each component where existed fluid movement possiblely occurred cavitation erosion.Cavitation erosion causes loss edges,loss lumps,holes,cracks in major components of hydraulic machinery.On the basis of summarizing publications on cavitation erosion,nanomaterials and interrelated area,mutimodal structure WC-12Co coatings were deposited by HVOF,and the coatings' properties were studied by some tests.Structure characteristic of WC-12Co powders in infuence of coatings' anti-cavitation erosion capabilities were studied.The mechanism of mutimodal WC-12Co coatings' anti-cavitation erosion properties was confered.The microstructure and phase compositions were studied by SEM and XRD,the results showed that difference of powders' structure causes difference of coatings' microstructures,submicro crystal WC grains melted in surface and be in solid state but most nano crystal WC grains melted absolutely in spraying process,Nano crytal WC grains got more kinetic energy and hotenthalpy in spraying process,changed shape more adequately when knock againsted the substrates.The square measure of nano crystal WC grains touched with flame increased compared with submicro crystal WC grains,and the temperature of nano crystal WC grains was more high compared with submicro crystal WC grains,resulted in nano crystal WC grains oxidized and decarbonized more seriously.Microhardness and anti-wear capabilities of coatings were studied,micrographs after wear were analyzed by SEM,the results showed that microhardness of mutimodal structre WC-12Co coatings reached HV_0.21600,is equal to the microhardness of nanostructre WC-12Co coatings.In wear experiment,the anti-wear capabilities of mutimodal structre WC-12Co coatings was 3 times high than microstructre WC-12Co coatings because size of particles in WC-12Co powders decrease,resulted in size of WC particles in coatings decrease,much tiny crystalline grain boundary existed,resulted in combination intensity between particles in coatings enhanced. Anti cavitation erosion properties were studied by ultrasonic vibration cavitation equipment.Micrographs of the coatings after cavitaion test were analyzed by SEM. The results showed that high toughness and high combination intensity help coatings resist cavitation,size of particles in WC-12Co powders decrease,resulted in coatings were more dense,combination intensity between WC particles,layer in coatings were enhanced,resulted in anti cavitation capabilities of WC-12Co coatings were enhanced,the content of nano size WC particles in WC-12Co powders increased contibuted to anti cavitation capabilities of WC-12Co coatings enhanced.Considering the results of the above tests all-around,difference of powders' structure causes difference of coatings' microstructures,nano crytal WC grains got more kinetic energy and hotenthalpy in spraying process,changed shape more adequately when knock againsted the substrates,resulted in size of WC particles in coatings decrease,Wc-12Co coatings were more dense;Size of WC particles in coatings decrease and much tiny crystalline grain boundary existed resulted in combination intensity between WC particles and layer in coatings.Combination intensity between WC particles and layers in coatings contributed to anti wear and anti cavitation capabilities of WC-12Co coatings.