| The multi-principal alloy design concept is a new alloy design method.This design mode breaks the traditional alloy design concept.The obtained high-entropy alloy has unique effects and excellent performance.However,the new alloy design concept has not been used for intermetallics so far.This paper takes the lead in applying the multi-principal alloy design concept to intermetallics,establishes a high-entropy intermetallics model,theoretically analyzes its practical availability,proposes a composition design method,and studies its microstructure and properties.High-entropy intermetallics are an intermetallic compound with a long-range ordered crystal structure,at least one sublattice is randomly occupied by three or more atoms in an(equa)equimolar ratio,and the intermetallic compound phase volume fraction is at least 75% or more.Thermodynamic analysis shows that the entropy of high-entropy intermetallics is higher than that of traditional intermetallic compounds,lower than that of high entropy alloys,and has lower Gibbs free energy.The kinetic analysis shows that atoms in high-entropy intermetallic compounds do not diffuse efficiently,and the nucleation and growth processes of alloys are easily inhibited.Based on the analysis of the occupancy rule of the third component and the formation conditions of the pseudobinary system,the basic rules for the elemental selection of high-entropy intermetallics are proposed in this paper:(1)Most of the elements in the principal elements occupying the same kind of sublattice are similar in nature;(2)The nature of most of the elements between the principal elements occupying the heterogeneous sublattice differ greatly,or can form compounds with similar stoichiometric ratio;(3)The principal elements simultaneously occupying many kinds of sub-lattice are used as adjustable factors to coordinate the imbalance of stoichiometric ratios.A design method for high-entropy intermetallics is proposed and three model alloys HEI1,HEI2,and HEI3 are designed.The calculation methods for ?Sconf,VEC,?Hmix,and ? parameters in high-entropy intermetallics have been proposed.Studies on the HEI1 type intermetallics show that the main phase of the(X1,X2,...,Xn)3Al alloy systems is B2 structures,forming B2 type high entropy intermetallic compounds,which have higher hardness and strength,lower Plasticity.By adjusting the type and content of alloying elements,the alloy phase composition can be changed from B2+FCC?B2+FCC+BCC?B2+BCC.Studies on the HEI2 type intermetallic compounds show that Ni3(X1,X2,...,Xn)alloy systems have a solidified structure of L12+FCC.When only Al,Si,and Ti are present,L12 type single-phase high-entropy intermetallics are formed,and Mn,Fe,V,and Cr are added to obtain L12 type high-entropy intermetallics containing FCC phases,which have good plasticity,and better overall performance under suitable elemental composition.Co3(X1,X2,...,Xn)alloy systems are mainly L12+B2 phase and forms L12 type high-entropy intermetallics containing B2 phase,which have higher strength and lower plasticity.Studies on the HEI3 type intermetallic compounds show that(Co,Ni)3(X1,X2,...,Xn)alloy systems mainly form(FCC + L12)tissue,forming L12 type high-entropy intermetallics containing an FCC phase.In the(Fe,Co,Ni)3(X1,X2,...,Xn)alloy system,a structure in which an ordered intermetallic compound phase and an disordered solid solution phase coexist is formed.By adjusting the content of Fe,the solidification and mechanical properties of the alloy can be controlled to some extent.Based on the study of the three types of intermetallic compounds HEI1,HEI2 and HEI3,the microstructure and properties of L12/B2 high-entropy intermetallics are obtained: In Fe-Co-Ni-Al-Si-V-Ti-Cr system,Al and Ti are conducive to the formation of B2 phase;V and Cr are conducive to the formation of disordered FCC phases;when the contents of Fe and Cr are similar,BCC phases are easily formed;Si and Ti are easily aggregated at grain boundaries;L12+FCC tissue is formed when the L12 type high-entropy intermetallics containing FCC phases is formed,and the plasticity is better;when the L12 type high-entropy intermetallics containing B2 phase and the B2 type high-entropy intermetallics are formed,the compounds have a solidified structure such as B2+L12,FCC+B2,and have a high strength.In this paper,it is confirmed that the model of high-entropy intermetallics can obtain simple crystal structure and phase composition,and it also basically ascertains the influence of each element and its content on the crystal structure,which lays the foundation for the application of multi-principal alloy design concept in intermetallics.A new type of intermetallic structural materials has been developed with certain scientific research and engineering application prospects. |
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