Composition Design And Property Research On Intermetallic Compound-based High-entropy Alloy

Superalloy is an indispensable key material for the development of the national economy and the construction of modern defense industry.Traditional solid solution matrix based superalloys represented by Ni-based superalloys have good high-temperature strength and plastic toughness.However,due to the limitation of the solid solution matrix and the melting point of the alloy,the properties has approached the limit.Intermetallic compound superalloys are based on ordered structures and usually have excellent high temperature stability,high temperature creep resistance and high strength.However,due to the poor plastic toughness and low high-temperature-strength,its application is greatly restricted.As a new type of alloy system,high-entropy alloys(HEAs)ususally have excellent comprehensive properties.However,its high-temperature properties that have been developed so far do not have obvious advantages compared with traditional high-temperature alloys.Therefore,in order to solve the above problems,this research focuses on combining the design ideas of HEAs and intermetallic compounds,meainwhile lying on the alloying law of traditional superalloys,to develop a new type of HEA material based on ordered matrix,which will have the plasticity of HEA and stability of intermetallic compound.According to the above idea,Fe_xCo_xNi_xCu_xTiZrHf,Co_xNi_xCu_xTiZrHf and Co_xCu_xTiZrHf series of HEAs were designed and prepared by vacuum arc melting.The crystal structure,microstructure and mechanical properties of these alloys after different heat treatment were systematically studied,and the electronegativity-related phase formation rule was proposed.The results showed that the as-cast Fe_0.75Co_0.75Ni_0.75Cu_0.75TiZrHf,CoNi Cu TiZrHf,and Co_1.5Cu_1.5TiZrHf alloys exhibit B2 ordered structure and excellent thermal stability.Among them,Fe_0.75Co_0.75Ni_0.75Cu_0.75TiZrHf alloy has the best comprehensive properties,and the crystal structure of the matrix is similar to CoZrand CoHf intermetallic compounds.This alloy not only has extremely high room temperature compressive strength(2.5GPa),high temperature yield strength(at 600°C,the yield strength can reach 1.5GPa;at 800°C and900°C,it can still reach 905MPa and 705MPa,respectively)and phase stability(the original crystal structure can be maintained at 1000°C without other phase),but also has a certain degree of plasticity.Comparing with the existing superalloys,it has better comprehensive properties.The successful preparation of this alloy provides the possibility and“stepping stone”for the development of new superalloysIn order to systematically explain the phase formation characteristics of HEAs based on intermetallic compounds,this study summarized the atomic radius difference and electronegativity difference related phase formation rule(?-?rule).Comparing with the former electronegativity related rules,this more reasonably rule is based on the direct electronegativity difference between the central atom and the neighbor atoms,and fully considered the interaction between atoms.It is found that the intermetallics or amorphous alloys tend to form when 0.2???0.4 and??5.5;the solid solution-based alloy will form when?<0.2 or?>0.4 and?<5.5;the eutectic alloy emerge in the vicinity of the two separating boundries due to its special solid solution+intermetallic compound structure.