Carbonization Mechanism Of Super Coarse W Powder And Preparation Of Super Coarse Grained WC-Co Cemented Carbide

Ultra-coarse-grained WC-Co cemented carbides have large grain size,high fracture toughness,impact resistance and thermal conductivity,and are widely used in high temperature resistant materials,corrosion resistant materials,wear resistant materials and other aspects.In this paper,four kinds of super-coarse W powders with different particle sizes were selected as raw materials to prepare super-coarse WC powders and super-coarse WC-Co cemented carbides by high temperature carbonization and sintering,respectively.The carbonation mechanism of ultra-coarse W powders was investigated by comparing the phase composition and micro structure of the carbonized products of different granularity W powders.The morphology and properties of WC grains in ultra-coarse WC powders with different contents of fine WC powders and WC-Co cemented carbide with different contents of Co were compared,the effect of fine WC powder and Co content on the preparation of ultracoarse-grained WC-Co cemented carbide was investigated.The results showed that:(1)The surface layer of carbonization products of W powder with different particle size is WC,and there is W2C phase in the carbonization products of W powder at 75?109?m.However,no W2C phase was detected at the temperature below 75?m,which indicated that the carbonization of W powder was a process of the diffusion of carbon atoms to the interior of W particles.The larger the W particle is,the longer the path of C atom diffusion to the core of W particle will be.In the same carbonization time,the more difficult the coarse W particle is to be completely carbonized.(2)The morphology and properties of WC-10Co cemented carbide prepared by WC powder with different granularity were compared.It is found that the average grain size,fracture toughness and mean free path of cobalt phase all decrease with the increase of the grain size of W powder,and the hardness values all increase with the increase of the grain size of W powder.(3)The morphology and properties of fine WC powder alloy in WC-Co cemented carbide were compared when 1wt%,3wt%and 5wt%fine WC powder were added into the WC powder size of 45?75?m,respectively,it was found that the average grain size,fracture toughness,density and mean free path of cobalt phase were firstly increased and then decreased with the increase of fine WC powder content,while the hardness was firstly decreased and then increased.it results show that the super-coarse grained cemented carbide with an average grain size of 11.34?m and fracture toughness of 22.70 MPa·m1/2 can be prepared by adding 3wt%.(4)Comparing the morphology and properties of WC-Co cemented carbides prepared by adding 3wt%fine W powder with three different particle size WC powders,it is found that the average grain size of the alloy increases more obviously with the addition of fine WC powder with smaller particle size.The dispersion and uniformity of WC cemented carbide with particle size of 25?45?m are good,and the surface of the cemented carbide is relatively smooth,the hardness of cemented carbide is 80.52HRA and 1190.4HV.The addition of fine WC powder can increase the densification of the alloy,and the densification of the WC powder with larger original particle size will increase more obviously after the addition of fine WC powder.(5)The average grain size of ultra-coarse WC-Co cemented carbides with low Co is larger than that of WC-10Co cemented carbides with more pores,and the alloy compactness is poor.The average grain size of low Co alloy decreases with the increase of Co content.