Mechanical Property And Deformation Mechanism Of FeMnCrCo System Dual-phase High Entropy Alloys

As newly discovered solid solution alloys in recent years,high-entropy alloys(HEAs)usually consist of five or more main elements with near equimole proportions.HEAs tend to form a simple solid solution with body center cube,face center cube and hexagonal or their mixed crystal microstructures.HEAs with unique structure show high strength,toughness,hardness,wear resistance,fatigue resistance and wear resistance,leading to a great application potential.To data,many researches focus on the preparation of new alloy systems,microstructure analysis and quasi-static mechanical properties.However,potential properties such as high-temperature creep,dynamic response under high strain rate and transformation-induced plasticity-assisted alloys need to be further studied.In this paper,the tensile properties under quasistatic and dynamic loading conditions,high temperature deformation behavior,and corresponding deformation mechanisms of AlxFeMnCrCoNi(Alx,x=0.4,0.5 and 0.6 in molar ratio)and Fe45Mn25Cr15Co15 high-entropy alloys with two-phase structure were systematically studied.The research results were summarized as follows:(1)The Alx alloys showed microstructures evolved from the cast dendrite to equiaxed grains after thermomechanical processing.The volume fraction of body-centered-cubic(bcc)phase increased due to the increase of A1 content.Yield strength and ultimate tensile strength significantly increased due to strengthening effects of solid solution,grain boundary and bcc phase.Specifically,serrated flow behaviors occurred at the medium temperature.The average serration amplitudes of these Al-containing alloys were larger than that of FeMnCrCoNi alloy due to the increased interaction between A1 solute and dislocation.(2)The tensile creep of Alx high-entropy alloys was investigated in the high-temperature range of 600-700?,The Al,alloys showed high creep resistance due to strengthening contribution from elemental Al.The Al0.4 alloy exhibited a stress-dependent transition from the low-stress region to high-stress region.The Al0.6 alloy showed declined creep resistance compared to the Al0.4 alloy,which was ascribed to the higher activation volume and stacking-fault energy in the former alloy.Specifically,the intragranular formation of Cr-rich a precipitation was widely found in the fcc grain among testing conditions,indicating a striking atomic diffusion process due to the limited entropic stabilization in Alx alloys.(3)The effect of strain rates on tensile behavior of Al.high-entropy alloys was investigated.Yield stress increased significantly but ductility slightly declined with the increase of strain rate.The Al0.4 alloy exhibited a larger strain-rate sensitivity than Al0.6 alloy owing to the larger grain size and smaller activation volume in former.Johnson-Cook constitutive model considering the effects of strain rate and strain on the flow stress was utilized to describe the plastic deformation behavior.Compared to quasi-static tension,the higher dislocation density was main characteristic of microstructures for dynamic deformation.An evolution from ductile to quasi-cleavage fracture was revealed due to the increase of volume of bcc phase and strain rate.(4)Through the adjustment of stability of phase,Fe45Mn25Cr15Co15 high entropy alloy was designed.Fe45Mn25Cr15Co15 alloy successfully combined good tensile strength and strain hardening capacity due to the introduction of the transformation-induced plasticity-assisted(TRIP)deformation mechanism.The increased strength was ascribed to a large amount of solid solution strengthening and the increase of interface density,while the plasticity maintained at a high level can be attributed to displacement plasticity and deformation induced hardening.