Preparation Of Pre-Solid Solution Composite Carbides And Its Effect On The Structure Of Cemented Carbides

Due to its high hardness,high wear resistance,high strength and high fracture toughness,cemented carbides has been widely used in cutting tools,drilling tools and wear-resistant parts.The rapid development of modern industry is increasingly demanding on the strength and toughness of cemented carbides.At present,it is an effective way to obtain uniform,fine structure and improve the strength of alloy.In this paper,the pre-solid solution composite carbide has been prepared,and the influences of the pre-solid solution composite carbide on the microstructure of the alloy have been studied by combining the experiment with the thermodynamic calculation.In addition,the influences of raw material composition on the solid solution composite carbide and spinodal decomposition after aging have been studied.The main research contents and innovation points of this work are as follows:(1)Based on carbon reduction at high temperature,(W,Ti,Ta)C composite carbide powder with the average particle size of 1.1?m has been prepared and applied to the preparation of WC-8wt.%Co based cemented carbides.Two groups of cemented carbides with the same chemical composition WC-Co-(W,Ti)C-TaC and WC-Co-(W,Ti,Ta)C,WC-Co-Ti(C,N)-(W,Ti)C-TaC and WC-Co-Ti(C,N)-(W,Ti,Ta)C have been prepared under vacuum sintering at 1450°C.Combined with thermodynamic calculation and experimental characterization of microstructure,the influence of(W,Ti,Ta)C composite carbide on the microstructure of cemented carbides has been studied.It is revealed that the pre-solid of Ta can significantly improve the thermodynamic stability of(W,Ti)C.With the traditional(W,Ti)C and TaC carbides replaced by(W,Ti,Ta)C composite carbide,a “core-shell” structure with “white core” can be detected in the cubic phase.Besides,due to the higher thermodynamic stability of(W,Ti,Ta)C composite carbide,the gradient layer thickness of the gradient cemented carbide can be significantly reduced by doping(W,Ti,Ta)C.(2)Seven groups of(W,Ti,Zr)C composite carbides have been prepared at 2200°C carbiding 3h when the WC content is 0wt.%,5wt.%,15 wt.%,25 wt.%,35 wt.%,45 wt.%,60 wt.%.Results show that the WC priority solid solution to the TiC form(W,Ti)C composite carbide in the process of sintering.(W,Ti)C carbide and ZrC solution into(W,Ti,Zr)C composite carbides,Some of(W,Ti)C carbide fused to ZrC.And with the addition of WC,the trendency of(W,Ti)C composite carbide entry to the ZrC is very small.The addition of WC will slow down the solid solution of composite carbides.(3)Three groups of cemented carbides have been prepared by SPS when the WC content is 0at.%,20 at.%,45 at.% and the influences of WC on the solid solution of(W,Ti,Zr)C composite carbides have been studied.Results show that(Ti,Zr)composite carbide almost completely solid solution without adding WC.the sample of 20 at.% WC was added,WC and TiC priority solid solution(W,Ti)C carbide.However,the sample of 45 at.% WC was added,the WC was not completely solid with TiC.(4)The preparation of the three groups(W,Ti,Zr)C composite carbides have been aged at 1500°C holding 10 h.In addition,the spinodal decomposition of(W,Ti,Zr)C composite carbide has been studied after aging.Results showed that the WC content is 0at.% and 20 at.%,(W,Ti,Zr)C composite carbides are decomposed into rich Ti carbides,when WC content was 45 at.%,the decomposition products are rich Zr carbide,rich Ti carbide and WC,the grain size can reach nanometer size.