Effects Of MWCNTs And SiCw On Microstructure And Properties Of WC-9Co Cemented Carbides

Cemented carbide is a composite material made of refractory metal compounds（hard phase）and bonded metal（binding phase）by powder metallurgy,which is widely used in the field of cutting tool materials.In this study,WC-9Co cemented carbides with cubic carbide free layer were taken as the research object.The effects of multi-walled carbon nanotubes（MWCNTs）,silicon carbide whisker（SiCw）and the synergistic effects on their microstructure and properties were explored respectively.The mechanism of MWCNTs and SiCw in WC-9Co cemented carbides was analyzed.Finally,a WC-9Co cemented carbides with the best comprehensive properties was obtained.Firstly,the effects of different MWCNTs contents on the microstructure and properties of WC-9Co cemented carbides were studied.The results showed that the addition of appropriate MWCNTs can reduce the grain size of WC,promote the growth of alloy gradient layer,improve the hardness and bending strength,and reduce the friction coefficient of the alloy.With the addition of MWCNTs,the gradient layer thickness of the alloy continued to increase from 13.3μm to 35.6μm.When the addition amount of MWCNTs was 0.08 wt%,the WC grain size of the alloy reached the minimum of 1.35μm,and the hardness and bending strength reached the peak value of1330 HV20 and 2798 Mpa,respectively.At the same time,the alloy had the best wear resistance.The relative density and fracture toughness of the alloy increased continuously with the addition of MWCNTs.It was found that the main mechanism of MWCNTs in the alloy were bridging,crack deflection,pull-out,and network strengthening effect formed in the cobalt phase.However,the addition of excessive MWCNTs led to aggregation in the alloy,which reduced the bonding strength of the hard phase and the bonding phase,and decreased the hardness and bending strength of the alloy to varying degrees.Secondly,the effect of different SiCw content on microstructure and properties of WC-9Co cemented carbide was studied.The results showed that a proper amount of SiCw addition can refine WC grain,promote the growth of alloy gradient layer,improve the hardness,fracture toughness,bending strength,and reduce the friction coefficient of the alloy.The hardness,fracture toughness and bending strength of the alloy reached the maximum values of 1294 HV20,15.02Mpa·m^1/2 and 2757 Mpa,respectively.When the SiCw content was 0.6 wt%,the alloy possessed the best wear resistance.The mainly mechanism of SiCw in the alloy were pull-out,bridge connection,diffusion strengthening,solid solution strengthening and residual compressive stress strengthening due to the thermal mismatch between SiCw and matrix.Compared with MWCNTs,SiCw was inferior in strengthening and toughening effect on WC-9Co alloy.While an excess addition of SiCw would inhibit the formation of gradient layer,which was not conducive to the densification of the alloy and finally lowered the alloy properties.The increase of sintering temperature contributed to the densification of the alloy,when the sintering temperature was 1450℃and 1470℃,the WC-9Co-SiCw alloy obtained a better mechanical properties.Finally,on the basis of the above experiments,the WC-9Co-MWCNT-SiCw alloy with the best comprehensive properties was obtained by the Minitab and the method of three-factor and three-level orthogonal experiment.