Alloy Design Based On Data Model And Deformation Behavior Of FeNiCrAl Based Multi-principal Element Alloys

Multi-principal element alloys（MPEAs）,is a new alloy system proposed and developed in recent years,which is composed of 4～6 alloy elements mixed according to equal or near equal molar ratio.Due to the high entropy effect caused by the mixing of various alloying elements,it tends to form solid solution with simple structure rather than the intermetallic compound.Therefore,multi-principal element alloys generally have excellent mechanical properties,good wear and corrosion resistance,high temperature stability and oxidation resistance.Due to the diversity of high entropy alloy composition,it is very important to screen the appropriate elements and determine the reasonable element ratio for the design of new alloys.Based on machine learning data modeling,combined with simulation calculation and experimental verification,this paper is committed to developing new multi-principal element alloys with excellent comprehensive properties.In this paper,machine learning method is used to construct a multi principal component alloy component hardness relationship model to obtain the impact of various alloy elements on hardness.Through sensitivity analysis,Al element is the key factor affecting the hardness of Fe-Ni-Cr-Al based MPEAs,followed by Fe element,and Cr is equivalent to Ni elements.Based on the constructed element-hardness relationship model,FeNiCrAlx based MPEAs and（Fe Ni）x Cr Al based MPEAs were designed,providing a foundation for accelerating the composition design of new alloys.Towards the high temperature application of MPEAs,a relationship model between alloy elements,temperature,and high temperature yield strength was constructed by using machine learning methods,and the reasonable atomic ratio of Al element was determined,and FeNiCrAl x（x=0.8,1.0,1.2）based MPEAs was designed.Based on the melting characteristics of the（Fe Ni）x Cr Al based MPEAs,the relationship model of alloy composition,phase structure,and melting range was constructed by using machine learning method and a novel Fe2.5Ni2.5Cr Al MPEA was designed.The designed FeNiCrAlx（x=0.8,1.0,1.2）MPEAs were experimentally prepared and characterized.The experimental results show that the content of Al element has a significant impact on the phase structure,microstructure,hardness,and wear resistance of the alloy.FeNiCrAlx（x=0.8,1.0,1.2）MPEAs are composed of B2/BCC phases,and the volume fraction of B2 phase increases with the increase of Al content.The dendrites in the alloy are rich in Cr and Fe elements,while the grains are rich in（Al,Ni）elements.With the increase of Al content,the Vickers hardness increases from 457HV（x=0.8）to 486HV（x=1.2）.The friction coefficient and wear rate gradually decrease,and the wear resistance is significantly improved.The wear mechanism of the alloy is also closely related to the Al content,with the increase of the Al element content from x=0.8 to x=1.2,the main wear mechanism of the alloy changes from adhesive wear to abrasive wear,accompanied by oxidation wear.FeNiCrAlx（x=0.8,1.0,1.2）MPEAs exhibit relatively high strength and plasticity,and also have a high specific yield strength.The yield strength of FeNiCrAl1.2 alloy can reach 397.6MPa at 800℃,and the specific yield strength can reach 61.6 MPa·cm³/g.The oxidation resistance of FeNiCrAlx（x=0.8,1.0,1.2）alloy at 1000℃was further investigated.FeNiCrAl alloy has the most excellent oxidation resistance,with the main oxidation products of Al2O3,Cr2O3,Fe2O3,and Fe Cr2O4.Combined with oxidation kinetics analysis and oxidation morphology,the high-temperature oxidation mechanism of the alloy was further revealed.This series of alloys have a broad application prospect in the high-temperature field.A novel Fe2.5Ni2.5Cr Al MPEA was prepared and characterized.It was compared with Fe1.5Ni1.5Cr Al alloy and the reported Fe2Ni2Cr Al alloy to verify the superiority of the performance of Fe2.5Ni2.5Cr Al MPEA.Fe1.5Ni1.5Cr Al alloy has a BCC/B2structure,Fe2Ni2Cr Al alloy and Fe2.5Ni2.5Cr Al alloy have a typical FCC+BCC/B2dual phase structure.DSC analysis shows that Fe2.5Ni2.5Cr Al alloy has a relatively narrow melting range,and the predicted values are in good agreement with experimental results,which proves the reliability of this design concept.The Fe2.5Ni2.5Cr Al alloy exhibits high hardness and modulus,with an average nanohardness and elastic modulus of 5.7±0.025GPa and 205.8±0.025GPa,respectively.The reciprocating friction tests show that Fe2.5Ni2.5Cr Al alloy has a lower average friction coefficient and wear volume loss during reciprocating friction,exhibiting a complex wear mechanism of abrasive wear,adhesive wear,and oxidation wear.The compression mechanical properties of Fe2.5Ni2.5Cr Al alloy at room temperature and high temperature were further studied.This alloy has high fracture strength（2315MPa）and plastic strain（50.13%）,and shows good work hardening ability.The thermal compression deformation behavior of FeNiCrAl alloy and Fe2.5Ni2.5Cr Al alloy were further studied under temperature of（800-1100℃）and strain rate of(0.001-1s^-1),the constitutive equation of the alloy was constructed.The thermal activation energy of the FeNiCrAl MPEA was 376.6 k J/mol,and the thermal activation energy of the Fe2.5Ni2.5Cr Al MPEA was 315.9 k J/mol.Fe2.5Ni2.5Cr Al alloy has a lower thermal activation energy and is more prone to deformation at high temperatures.For FeNiCrAl alloy,the prediction performance of Arrhenius type constitutive equation,artificial neural network（ANN）and support vector machine（SVM）constitutive equation is compared.The results show that the SVM constitutive model has high accuracy,confirming the advantages of machine learning methods in constructing the constitutive equations of multi-principal element alloys.To obtain a suitable hot working process,the hot working diagrams of FeNiCrAl alloy and Fe2.5Ni2.5Cr Al alloy were drawn.The most suitable hot working process parameters for FeNiCrAl MPEAs are at temperature of（>950℃）and strain rate of(<0.01s^-1).The optimal thermal processing parameters for Fe2.5Ni2.5Cr Al MPEAs are at temperature of（850-1020℃）and strain rate of(10^-2-10^-3s^-1).Using finite element simulation,the strain and stress distributions during thermal deformation of Fe2.5Ni2.5Cr Al alloy were revealed,and the instability during thermal deformation was predicted,which provided a theoretical basis for revealing the deformation mechanism of the alloy.Molecular dynamics simulation was used to analyze the lattice structure,atomic shear strain,and dislocation motion of the alloy during compression deformation and nano wear.The compression deformation mechanism and friction wear mechanism of the alloy were revealed from the atomic scale.The deformation behavior of Fe2.5Ni2.5Cr Al alloy was further studied by tensile test.The alloy has no necking,high yield strength（596MPa）,fracture strength（929MPa）and uniform elongation（21.4%）,and shows good work hardening ability and thermoplastic forming ability.Precipitation strengthening is the main strengthening mechanism of the alloy.After tensile deformation,there are a large number of dislocations and deformation twins in the precipitate phase and near the phase interface.The deformation and strengthening mechanism were revealed,which originated from the coordinated effect of high-density dislocation slip and mechanical twinning in nano coherent dual phase of Fe2.5Ni2.5Cr Al alloy.