Control Of Lamellar Microstructure Of WC Preform And Its Influence On The Properties Of WC/Cu Composites

WC/Cu composites have excellent comprehensive properties combined with high strength,high hardness of WC and high thermal conductivity of Cu.It has wide application in electrical contact materials such as witches,relays,contactors.Copper-based composites are prepared by powder metallurgy,casting,internal oxidation and melt impregnation.Among them,in the composites prepared by melt infiltration combined with freezing casting method.The reinforcement and the matrix of the composites are alternately arranged in a lamellar structure,which can exert the characteristics of the reinforcement and the matrix to a greater extent.This method is widely used in the field of aluminum-based composites,which improves the strength and toughness of the composites.If the copper-based composites is prepared by this method,the excellent properties of the reinforcement and copper can be combined.However,the microstructure and performance of composites prepared by this method is affected by the structure of preforms,and there are many factors that affect the structure of preforms.Therefore,it is necessary to control the structure.In this paper,WC preforms were prepared by directional freeze-casting method,and laminated gradient WC/Cu composites were prepared by pressureless infiltration.The formation mechanism and control of the lamellar structure of WC preforms and its influence on the microstructure and properties of the composites are studied.The results are as follows:(1)The WC preforms prepared by the directional freeze-casting method present lamellar gradient structure parallel to the freezing direction,which presents porous,transition and lamellar regions from the cold end.With the increase of solid content of WC,the thickness of WC preforms increases,but the spacing between lamellar and lamellar film and the porosity of WC preforms decreases.(2)The structure of WC preforms is controlled by changing freezing temperature,slurry temperature,body diameter and body height.The results show that freezing temperature and slurry temperature have significant effects on the structure of WC preforms.The optimum technological parameters for the preparation of WC_I,WC_II,WC_IIIand WC_IVstructural preforms are determined.The lamellar thickness and interlamellar space of WC_?preform are uniform,and the average value was about35?m.(3)The Cu melt was completely infiltrated into the pores of the WC preforms at1250?for 60 minutes.The lamellar gradient structure of the WC preforms is completely preserved in the WC/Cu composites.When the content of WC increased from 15vol.%to 25vol.%,The average thickness of the metal lamellar of the composites was decreased by 20?m,and the yield strength and hardness are increase to 814MPa and 322HV respectively.(4)WC_I/Cu,WC_?/Cu,WC_?/Cu and WC_?/Cu composites are obtained by the infiltration Cu melt in 20vol.%WC preforms with different structures.The microstructure of WC_?/Cu composite is uniform,which Vickers hardness is 344HV,and that is nearly five times higher than pure copper.The thermal diffusivity of WC_?/Cu composite at room temperature is close to the pure copper and has excellent comprehensive properties.