Preparation Of Rare Earth Modified Cobalt Composite Powder And Its Hard Alloy By Spray Conversion

Because of its high hardness and high wear resistance,WC-Co cemented carbide is widely used in cutting tools,drilling tools,wear and corrosion resistance parts and other fields.The grain size of WC grain will directly affect the comprehensive performance of hard alloy.Inhibitors can inhibit the grain growth of WC grains in the sintering process of WC-Co cemented carbide,but the traditional method of adding inhibitors into WC-Co composite powder by high-energy ball milling has some shortcomings,such as uneven mixing and easy accumulation of surface defects.The modification of Co phase can promote the densification of hard alloy,strengthen the toughness of hard alloy and improve the comprehensive properties of the alloy.In this study,cobalt acetate,yttrium nitrate and WC powder were used as raw materials,and WC-Co-Y₂O₃composite powder with pure phase and uniform size was prepared by spraying,calcination,reduction and ball milling.WC-Co-Y₂O₃carbide was prepared by discharge plasma sintering（SPS）.The effects of composition design and sintering process parameters on the microstructure and properties of samples were also investigated.The experimental results are as follows:（1）Spray conversion makes the solution containing Co and Y elements form spheroidal amorphous precursor powder.Calcination makes the precursor powder decompose into Co₃O₄-Y₂O₃,and the particle size of powder particles is greatly reduced and aggregated into clusters.Through H2 reduction,the oxide powder is reduced into ultrafine Co-Y₂O₃powder and ball ground with WC powder to prepare WC-6Co-Y₂O₃composite powder.（2）The WC-6Co cemented carbide was prepared by SPS sintering,and its microstructure and mechanical properties were analyzed.The best performance of cemented carbide was determined when the sintering temperature was 1300℃and the holding time was 5 min.The density,hardness and fracture toughness of WC-6Co cemented carbide sintered by this process are 98.78%,1926 HV₃₀,8.83 MPa·m^1/2,respectively.（3）The effects of addition of Y₂O₃on the microstructure,mechanical properties,friction and wear properties and corrosion resistance of WC-6Co-xY₂O₃cemented carbide were studied.With the addition of Y₂O₃,the grain size of WC carbide decreases,and its density,hardness,toughness,wear resistance and corrosion resistance all show a trend of increasing first and then decreasing.The results show that WC-6Co-1.5Y₂O₃carbide has the best performance.Its density,hardness and fracture toughness are99.51%,2061 HV₃₀,8.83 MPa·m^1/2,respectively.（4）The modification of Co bonding phase by Y₂O₃plays an obvious role in the corrosion resistance of cemented carbide.The addition of Y₂O₃greatly improves the acid corrosion resistance of cemented carbide,and has little effect on the corrosion performance under alkaline conditions.Under alkaline conditions,the corrosion of WC grains is mainly,Co will react with alkaline solution to form Co（OH）₂and adhere to the alloy surface,thus preventing further corrosion.Under acidic conditions,it is mainly Co bonding phase corrosion,and Y₂O₃dissolved into Co phase will play a role in strengthening the bonding phase.