Microstructure And Mechanical Properties Of CoCrFeNiX_0.4(Al,Ta,Nb) High Entropy Alloy With Equal Atomic Radius

High-entropy alloys are composed of at least 5 elements,each of which has a composition between 5%and 35%.At first,because of its easy formation of simple single-phase solid solution and stable properties of the alloy,it attracted extensive research by scientific researchers.Due to the greater degree of freedom in the composition range,with the deepening of research,people have discovered the existence of two-phase or three-phase high-entropy alloys,and the existence of these phases affects the thermal stability and mechanical properties of the alloy.In order to further study the reasons for the formation of SS in HEAs,researchers have made specific analysis on the decisive factors affecting the formation of HEA solid solution phase,such as atomic radius,valence electron concentration,and electronegativity.The factors for the formation of various types of solid solution phases are summarized.However,in previous studies,researchers have neglected to control multiple sets of variables to study the influencing factors of solid solution formation.In this work,we focused on the effects of the formation of solid solution phases in high-entropy alloys when multiple sets of variables are consistent.standard.At the same time,the microstructure and mechanical properties of CoCrFeNiX(Al,Ta,Nb)high-entropy alloys with equal atomic radius were studied,and the fundamental differences in mechanical properties of the alloys were explained from the aspects of solid solution strengthening,precipitation strengthening,and grain boundary strengthening.the reason.Finally,in view of the high cost of preparation of CoCrFeNiTa alloy,the substitution of Ta atoms was discussed,and the C oCrFeNiTa0.2Nb0.3 high-entropy alloy alloy was successfully prepared,which can perfectly replace CoCrFeNiTa0.4 highentropy alloy from microstructure to mechanical properties.Alloy,and save 29%in cost,for the future application of CoCrFeNiTa alloy proposed a good alternative.The main research contents are as follows:1.By adding Al,Ta,Nb of equal atomic size to the CoCrFeNi alloy,under the premise of controlling the added atomic size,the mixing entropy of the system,the same atomic radius difference,and the extremely similar mixing enthalpy,other factors on the formation of solid solution phase are studied Impact.It is found that electronegativity plays a leading role in determining the distribution of precipitated phase components;the melting point has a great relationship with the formation of TCP phase,and the addition of high melting point elements is easy to form TCP phase.2.By comparing the degree of FCC phase lattice distortion in different alloys,the nanoindentation experiment is used to verify the effect of solid solution strengthening and it is found that lattice distortion does not necessarily produce a good solid solution strengthening effect.By comparing the hardness and volume fraction of the precipitated phase,it is obtained that precipitation strengthening is the dominant factor in determining the mechanical properties of the CoCrFeNiX alloy.Through the statistics of grain size,it is found that grain boundary strengthening has similar strengthening effects in CoCrFeNiTa0.4 and CoCrFeNiNb0.4 alloys.In the CoCrFeNiTa0.4 alloy,the fine eutectic structure is often accompanied by the formation of low-angle grain boundaries and deformed grains,which helps to improve the strength of the alloy.3.By substituting Nb atoms for part of the Ta atoms in the CoCrFeNiTa alloy,the CoCrFeNiTa0.2Nb0.3 high-entropy alloy was successfully prepared under the premise of a cost saving of 29%.Compared with CoCrFeNiTa0.4 high-entropy alloy:(a)It has' a similar crystal structure and phase hardness values.(b)In terms of the volume fraction of the precipitated phase,the two are also the same and have the same phase distribution type.(c)In terms of macro-mechanical properties,it shows high compressive yield strength and hardness.