Preparation And Tribological Properties Of Carbide Ceramics（TaTiVMM’）C₅

In recent years,high entropy ceramic materials designed and prepared by means of the concept of"high entropy"in high entropy alloy have better comprehensive properties than each element,which has become a research hotspot in the field of ceramic materials.High entropy transition metal carbide ceramics have high hardness and elastic modulus,excellent oxidation resistance and ablative resistance,and have good application prospects in engine,hypersonic vehicle leading edge,wear-resistant materials and other fields.At present,some progress has been made in the design,preparation and properties of high-entropy carbide components.However,the diversity of the design of high entropy carbide components makes the relationship between the components,preparation technology,phase,microstructure and properties very complicated.The influence of element composition on microstructure and properties of high entropy carbide ceramics is worth studying.Three component（TaTi V）C₃ solid solution and four component（TaTi VM）C₄ and five component（TaTi VMM’）C₅ high entropy carbide ceramics were prepared by spark plasma sintering（SPS）using commercial carbide powders.The effects of different elements on phase composition,microstructure,mechanical and tribological properties of high entropy ceramics were compared.The main conclusions are as follows.The（TaTi V）C₃ solid solution was prepared from TaC,Ti C and VC by non-pressing sintering,hot pressing sintering and SPS.TaC,Ti C and VC carbides have good solid solution ability,and which can form single-phase face-centered cubic structure（TaTi V）C₃ solid solution at 1600 ^oC.With the increase of sintering temperature,the solution reaction of carbide becomes fuller,the distribution of metal elements tends to be uniform,and the grain size increases from 1.9μm to 2.7μm.The hardness of（TaTi V）C₃ solid solution is about 21-22 GPa.It has good friction and wear characteristics,and the average friction coefficient at room temperature and 600 ^oC is 0.4 and 0.3,respectively.The average specific wear rate at room temperature and 600 ^oC is 1.2×10^-7 mm³·N^-1·m^-1 and 4.4×10^-6 mm³·N^-1·m^-1.The single-phase and densification temperatures of（TaTi VM）C₄（M=Mo,Nb,W）high-entropy carbides increased after the introduction of the fourth metal component.The hardness of（TaTi VW）C₄ decreased with the increase of temperature,and the fracture toughness of（TaTi VW）C₄ increased.The fracture toughness of（TaTi VW）C₄ sintered at2100 ^oC was 5.6 MPa?m^1/2.（TaTi VMo）C₄ has a hardness of about 19-20 GPa.（TaTi VNb）C₄has a hardness of 17-20 GPa.The three quaternary high entropy carbides have excellent friction and wear characteristics.The average coefficient of（TaTi VW）C₄ at room temperature and 600 ^oC is about 0.4-0.6,and the average specific wear rate is(10^-7-10^-6)mm³·N^-1·m^-1.（TaTi VMo）the average friction coefficient at room temperature is about 0.4-0.5,and the average specific wear rate is(10^-8-10^-7)mm³·N^-1·m^-1,and the average friction coefficient at 600 ^oC is about 0.4-0.7,and the average specific wear rate is 10^-7mm³·N^-1·m^-1.The average friction coefficient of（TaTi VNb）C₄ sintered in 2050 ^oC is about 0.4 at room temperature and 600 ^oC,and the average specific wear rate is(10^-6-10^-5)mm³·N^-1·m^-1.At the same time,the fourth and fifth components were introduced,and the five-element high entropy carbide ceramics（TaTi VMM’）C₅（M,M’=Mo,Nb,W）were prepared by SPS,and compared with（VNb TaMo W）C₅,（VNb Ti Mo W）C₅ and（Nb TaTi Zr Hf）C₅.The density of the prepared five-element high entropy carbide varies with the component.The introduction of Mo-W combination and Nb-W combination leads to a decrease in the density of five-member high-entropy carbide relative to ternary and four-member ceramics,and the introduction of Nb-Mo combination leads to a decrease in the density of five-member high-entropy carbide relative to ternary carbide.The grain size of five-element high entropy carbide increases with increasing temperature.Sintered at 1800 ^oC to 2000 ^oC,the grain size of（Nb TaTi Zr Hf）C₅ is only 0.8μm to 1.2μm.The hardness of five-component high-entropy carbides is almost invariable with sintering temperature and ranges from 17 GPa to 20 GPa（except（VNb Ti Mo W）C₅）.Similar to the four-membered high-entropy carbide,the five-membered high-entropy carbide has the friction and wear characteristics,the average friction coefficient at room temperature is less than 0.8,and the average friction coefficient of（Nb TaTi Zr Hf）C₅ is as low as 0.29.The high temperature friction coefficient increases slightly.The average specific wear rate of five-element high-entropy carbides is about 10^-8-10^-5 mm³·N^-1·m^-1.