Study On Preparation And Properties Of High Entropy Composite Cemented Carbide

Due to its excellent comprehensive mechanical properties,WC-based hard alloys are extensively used in precision machining tools and precision components,serving high-precision machining fields such as aviation,medical,and military industries.Currently,China heavily relies on imported high-precision machining tools,mainly due to differences in material properties and preparation processes of tool raw materials.Although the addition of Co in traditional WC-Co cemented carbide promotes the sintering densification of the WC matrix,it also causes a significant decrease in the wear resistance of the hard alloy,ultimately affecting the service life of finished tools or components.Compared with traditional bonding metals,high-entropy alloys exhibit even more outstanding comprehensive mechanical properties.Among the CoCrFeNi Alx series of high-entropy alloy elements,Co,Fe,Ni,and Al possess excellent wetting properties with WC,making them hold enormous potential to become the bonding phase in WC-based hard alloys.This study focuses on the preparation and use of CoCrFeNi and CoCrFeNi Al_0.25high-entropy alloy ultrafine powders as the binder phase in WC-based cemented carbide.The high-entropy composite carbides were prepared using the spark plasma sintering method and compared to traditional WC-Co cemented carbide under the same processing parameters.The effects of ball milling time on the phase composition of the high-entropy alloy powders were studied,and their particle size and powder uniformity were analyzed through morphology characterization.The mechanical properties of the high-entropy composite carbide and traditional WC-Co cemented carbide were analyzed through various mechanical property tests,and the toughening mechanisms were investigated.Frictional properties of the high-entropy composite carbide and traditional WC-Co cemented carbide were compared through friction tests,and their wear mechanisms were analyzed through morphology characterization.Additionally,the effects of grain growth inhibitors on the mechanical and frictional properties of the cemented carbides were studied.The main conclusions are as follows:（1）By means of variable-speed high-energy ball milling for 40 hours,the two powders were sufficiently alloyed.CoCrFeNi appeared as a single FCC phase,whereas CoCrFeNi Al_0.25exhibited a weak BCC phase in addition to the FCC phase.The CoCrFeNi powder displayed an irregular spherical shape,with many small particles settling at the bottom,and aggregation phenomena of the powder were not obvious.Conversely,the aggregation of the CoCrFeNi Al_0.25powder was more conspicuous,and the particle size distribution was broader,with the fine powder being flocculent or flake-like,and the aggregated powder forming a quasi-spherical,large particle shape.The powder particle size was significantly reduced after ball milling,with the CoCrFeNi powder particle size being concentrated between 0.5～1.5μm,and the CoCrFeNi Al_0.25powder particle size being concentrated between 1.5～3μm.（2）There was no obvious decarburization or carburization phenomenon observed in all the samples after sintering.The grain size of the high-entropy composite hard alloy was smaller than that of the WC-Co hard alloy,and the growth inhibitor of the VC grain had less influence on the grain size of the high-entropy composite hard alloy.The hardness and flexural strength of the high-entropy composite hard alloy were both greater than those of the WC-Co hard alloy.Among them,the WC-H1VC had the best comprehensive performance,with a hardness,fracture toughness and flexural strength of 2031.2 HV,12.55 MPa·m^1/2,and1254.45 N/mm²,respectively.The strengthening mechanism of the high-entropy composite hard alloy was attributed to grain refinement,crack deviation,trans-granular fracture,and grain pull-out.（3）Under the same friction test conditions,the average friction coefficient of high entropy composite hard alloys is lower than that of traditional WC-Co,and the friction curve is more stable with smaller fluctuations.Under the same test conditions,the wear resistance of WC-H1 high entropy composite hard alloy is higher than that of traditional WC-Co hard alloy,especially under high loads and no lubrication,the wear amount is reduced by more than 90%.The wear mechanism of traditional WC-Co hard alloy is mainly abrasive wear,fatigue wear,and adhesive wear,while the wear mechanism of WC-H1 high entropy composite hard alloy is mainly abrasive wear and fatigue wear,with more obvious adhesive wear under high loads and no lubrication.The wear resistance of traditional WC-Co hard alloy and high entropy composite hard alloy is positively correlated with their mechanical properties,with hardness playing a dominant role.