Preparation,Microstructure And Properties Of Multicomponent Carbide Powders

Carbide ceramics have high strength and hardness,which were invented during the World War II.Although carbide ceramics have made great progress today,they are increasingly unable to meet the increasingly stringent service conditions.Therefore,inspired by high entropy alloys,people began to explore the preparation and microstructure of high entropy carbides.They are a single-phase solid solution formed by five or more metal components and carbon atoms with excellent properties such as high melting point and high hardness.At present,the research of high entropy carbides can be divided into bulk and powder,and some high entropy carbides have excellent mechanical properties and high temperature resistance.The research of high entropy carbides lays a foundation for the application of high entropy carbides.In this paper,ternary quasi-high entropy carbide(Ti,Ta,Nb)C powders and quaternary quasi-high entropy carbide(Ti,Ta,Nb,V)C powders were prepared by molten-salt-assisted method using metal powder,metal hydride powder and nano carbon powder as raw materials.However,when(Ti,Ta,Nb,M)C and(Ti,Ta,Nb,V,M)C(M=W,Mo,Zr)powders were prepared by the same process,they were not successfully prepared.When preparing ternary carbide(Ti,Ta,Nb)C powders,it is found that the preparation products of Na Cl as molten salt are Na Ta O₃,(Ti_0.33Ta_0.67)O₂and(Ti,Nb)C;The preparation product of KCl as molten salt is(Ti,Ta,Nb)C;The preparation products of Na Cl and KCl mixed salts as molten salts are Ta O₂and(Ti,Ta,Nb)C.At the same time,it is found that excessive nano-carbon powder can promote the formation of ternary carbide powders and reduce the preparation cost.And it is found that the oxidation resistance of(Ti,Ta,Nb)C with 3:1:1 molar ratio of Ti,Ta and Nb is better than that of(Ti,Ta,Nb)C with equal molar ratio of Ti,Ta and Nb.When preparing quaternary carbide powders,it is found that quaternary carbide(Ti,Ta,Nb,V)C powders without miscellaneous phases can be prepared by using Ti,Ta,Nb,V as metal components;The preparation products of Ti,Ta,Nb,Zr as metal components are Zr O₂and(Ti,Ta,Nb)C;The preparation products of Ti,Ta,Nb,Mo as metal components are Mo₂C and(Ti,Ta,Nb,Mo)C;The preparation products of Ti,Ta,Nb,W as metal components are WC,W₂C and(Ti,Ta,Nb,W)C.At the same time,it is found that the oxidation resistance of quaternary quasi-high entropy carbide(Ti,Ta,Nb,V)C powders with short holding time is better,which indicates that the more uniform the composition of them is,the worse the the oxidation resistance of them is.When preparing penta carbide powders,it is found that the preparation products of Ti,Ta,Nb,V,W as metal components are WC,W₂C,WC_1-Xand(Ti,Ta,Nb,V,W)C;The preparation products of Ti,Ta,Nb,V,Mo as metal components are Mo₂C and(Ti,Ta,Nb,V,Mo)C;The preparation products of Ti,Ta,Nb,V,Zr as metal components are Zr O₂and(Ti,Ta,Nb,V)C.Overall,from four to five metal components,although entropy increases a lot,W and Mo carbide appeared in the product.The Zr produced by Zr H₂decomposition reacts with O during heating and the product Zr O₂remains.Moreover,the oxidation resistance of quaternary quasi-high entropy carbide(Ti,Ta,Nb,V)C powders prepared by molten-salt-assisted method is better than that of ternary quasi-high entropy carbide(Ti,Ta,Nb)C powders.