Study On Synergistic Deformation And Solid Solution Strengthening Mechanisms Of Ni-Co-Cr Multi Component Alloy

In recent years,multi-principal elemental alloys have received widespread attention as new structural metal materials.Common examples include medium-entropy alloys with three elements,and high-entropy alloys with four or five elements.Unlike traditional alloy design based on a single element as the matrix,MPEAs are designed based on the concept of "multielemental equality." The mixing entropy of MPEAs makes it easy to form single-phase solid solutions with multiple principal elements.Currently,in the face-centered cubic Ni-Co-Cr system,it has been found that the equiatomic Ni Co Cr MEA exhibits excellent comprehensive mechanical properties at extreme temperatures,including abnormally high fracture toughness at 77 K,and a combination of high strength and high plasticity.However,research on the Ni-Co-Cr MPEA system is still mainly focused on the equiatomic Ni Co Cr alloy,and there is still a lack of systematic research on the precise mapping between MPEA composition and deformation mechanism,as well as the synergistic effects of grain structure changes on multiple deformation mechanisms.Additionally,research on the strengthening effect of elemental solid solution on mechanical properties is also relatively lacking.This study prepared 16 Ni-Co-Cr multi-principal elemental alloys based on the Ni-Co-Cr phase diagram,and investigated the influence of composition on synergistic deformation mechanisms.Based on this,alloy compositions with excellent mechanical properties were selected to explore the effect of grain size on the synergistic effects of multiple deformation mechanisms.Finally,elements were added to the selected alloy composition to investigate the effect of composition on solid solution strengthening.The results of this study are as follows:(1)By testing the mechanical properties of the solid solution alloy with four parting lines designed in the single-phase area of the Ni Co Cr phase diagram,the deformed samples were characterized by synchrotron radiation XRD,scanning electron backscatter diffraction and transmission electron microscope,and the dominant areas of dislocation,twinning and transformation in the single-phase area of the Ni Co Cr phase diagram were distinguished,and the multi mechanism collaborative deformation area with high strength and toughness was determined.In the collaborative deformation zone,Ni30Co45Cr25 alloy has a high elongation due to the dynamic Hall Petch effect.(2)Through recrystallization heat treatment at 1000 ℃,850 ℃ and 700 ℃ for the alloy in the cooperative deformation zone and tensile property test,it is found that the elongation of the samples at 1000 ℃ and 850 ℃ is greatly improved co MPared with the samples at 700 ℃.After the work hardening curve is calculated,combined with the EBSD characteristic analysis under different strain levels,it is found that the multi mechanism cooperative deformation exists when the average grain size is greater than the specific threshold,Otherwise,the synergistic effect of multiple deformation mechanisms disappears,leading to a significant decrease in plasticity.(3)By adding different strengthening elements and conducting mechanical tests on the alloy in the collaborative deformation zone,combined with the analysis of atomic volume mismatch,atomic size mismatch,and modulus mismatch during solution strengthening,it was found that the predicted atomic volume mismatch was consistent with the actual yield strength,while the predicted atomic size and modulus mismatch during solution strengthening was inconsistent with the actual yield strength.Considering that modulus mismatch leads to excessively high predicted yield strength,the solid solution strengthening effect is mainly caused by atomic volume mismatch,so the predicted value is consistent with the actual value.