First-Principles Study Of Mechanical Properties,surface Adsorption And Interface Bonding Of B2 Type FeAl

B2 type FeAl has not been able to achieve large-scale industrial applications due to its brittleness at room temperature and the sharp drop in strength after600?,and the deterioration of its creep resistance.However,because of its low cost of raw materials and its advantages of low density,high hardness,and corrosion resistance,it still attracts many researchers to in-depth exploration.Solid solution strengthening by alloying and compound strengthening by using the second phase are common methods for improving the above defects,but further studies have yet to be performed on the strengthening effect and the microscopic mechanism.In addition,the study of functionalization of FeAl has also helped it open up new applications.Therefore,it is of great significance to carry out research on the surface and interface of FeAl to achieve the functional application of FeAl and the development of metal matrix composites to meet the economic and social development.In this paper,the first-principles based on density functional theory are used to study the mechanical properties,surface and interface properties of B2FeAl-based intermetallic compounds.The main contents are as follows:?1?The mechanical properties and strengthening mechanism of B2 type FeAl for 15 elements of V,Sc,Mn,Si,Mg,Co,Zr,Cu,Zn,Nb,Cr,Mo,W,Ti and Ni were studied.The results show that the FeAl-Cr,FeAl-Ti and FeAl-Co systems are ductile materials,and the FeAl-Co system is the most ductile phase among these alloy phases,and its ratio of bulk modulus to Young's modulus is B/G=1.92,Poisson's ratio is v=0.28.The calculation of the electronic structure shows that the doping of Cr,Ti and Co may lead to the charge redistribution,the weakening of the Al-Al interaction,and strengthening of the Fe-Fe and Fe-Al interactions.?2?The mechanism of co-doping CrX?X=Mo,Ti,Si?on FeAl was studied.The results show that when CrX is co-doped,Al-Al interaction cannot continue to be weakened,even there is also a rebound.The interaction between Fe-Fe continues to be enhanced,and the interaction between Fe-Al has a weak enhancement in addition to the impaired CrSi co-doping.On the other hand,the introduction of X makes the anti-bonding interaction between Fe-Cr in the three systems significantly enhanced.?3?The calculation of adsorption energy of Cr,Ti and Co atoms in the FeAl?110?surface shows that the Cr and Ti atoms are most likely to be adsorbed on the LB-2Al site of the FeAl?110?surface,while the Co atom is most likely to be adsorbed on the short bridge sites,and the adsorption at each position is chemical adsorption.The calculation of Population shows that atomic adsorption causes redistribution of system charges.All the atoms on the FeAl?110?surface before adsorption are in a bonding state.After the adsorption,all atoms are also bonded in addition to the Fe-Fe bond of Co adsorption is in the anti-bonding state.The interaction of Al-Al and Fe-Al is weakened,and the interaction between Fe-Fe is weakened due to bond with Cr and Ti,showing a distinct ionic bond state.Compared with the interaction of Al-X,the interaction between Fe-X exhibits weaker covalent bond character.Adsorption energy calculations for gas adsorption indicate that CO₂ molecules are easily adsorbed at the TF-2Al site,SO₂ at the LB-2Al site and Cl₂ molecules at the short-bridge site.No CO₂ and SO₂ molecules are decomposed after adsorption,and Cl₂ molecules is decomposed at all adsorption sites.The charge of the system was redistributed after adsorption,and the bond population show that there is a strong covalent bond interaction between C-Fe₁₅5 atoms,while the C-Fe₂₀0 atoms is in a weakly anti-bonding states.After SO₂ adsorption,the strength of S-O covalent bond is weaker than that of C-O bond,while the O-Al bond is weaker than the S-O bond.The S-Fe bonds are all strong interactions of covalent properties.After adsorption,the two Cl₁-Fe bonds show covalent properties,while the Fe-Fe bond show an anti-bonding state.?4?The FeAl?110?/NiAl?110?interface was investigated by first-principles.Considering different stacking sequences,five interface models were established.The calculation of the adhesion work shows that the FeFe long Bridge site model has the largest work of adhesion.The calculation of the interface fracture indicates that the failure of the FeAl/NiAl interface may occur on the FeAl side or the NiAl side of the interface,but not at the interface.The calculation of the electronic structure shows that the Al atoms at the interface lose charge,while the Fe and Ni atoms get charge,and covalent bonds are formed at the interface.?5?The first-principle study of the FeAl?100?/TiC?100?interface was performed.Eight FeAl?100?/TiC?100?interface models were established by taking into account of the two termination of the FeAl?100?surface and four stacking sequences.The OT Al site model with Fe-terminated and the OT Fe site model with Al-terminated in the unrelaxed state have the largest adhesion work.After optimization,the interfacial spacing of these two models changed very little,and the work of adhesion increased to 14.44 J/m²and 12.47 J/m²,respectively.The calculation of the interface fracture indicates that the failure of the FeAl?100?/TiC?100?interface will occur at the interface or at the TiC side,but not at the FeAl side.The charge density map shows that there is a covalent interaction between Fe atoms and C atoms at the interface of Fe-terminated FeAl?100?/TiC?100?interface model.However,there is a large amount of charge aggregation between the C atoms and Al atoms at the interface of the Al-terminated FeAl?100?/TiC?100?interface model.The population calculation and layer-projected density of atates indicate that the covalent bonding between Al atoms and C atoms in the interface is the main reason of the interface formation.?6?Thefirst-principlescalculationswereperformedonthe FeAl?110?/?-WC?0001?interface.Considering the two termination of the?-WC?0001?surface and five stacking sequences,ten FeAl?110?/?-WC?0001?interface models were constructed.After optimization,the OT Fe site interface with W-terminated achieves the maximum adhesion work of 3.98 J/m²when the interface distance is 2.08?,and the C-terminated FeFe long bridge site interface achieves the maximum adhesion work of 4.74 J/m²with the interface distance1.23?.In general,the adhesion work of the C-terminated interface is greater than that of W-terminated interface.Calculations of interfacial fracture indicate that the failure of the two FeAl?110?/WC?0001?interfaces will occur at the interface and not at the FeAl or WC side.The calculation of the electronic structure shows that all W and Al atoms of W-terminated interface lose charge,while Fe atoms receive the charge.All Fe atoms and Al atoms of C-terminated interface provide charge,while C atoms receive the transferred charge.Both terminations of the FeAl?110?/WC?0001?interface contain ionic,covalent and metallic bonds.?7?First-principles calculation of FeAl?110?/?-Al₂O₃?0001?interface were performed.Considering different stacking sequences,four interface models were constructed.After optimization,The interface distance of the four interface models is greatly reduced.The FeFe bridge site interface achieves a maximum adhesion work of 13.77 J/m²with the interface distance 1.25?.The interatomic bond formation at the interface indicates that the O atoms of Al₂O₃ play a more active role in the formation of the FeAl?110?/?-Al₂O₃?0001?interface.The calculation of electronic structure shows that all Al atoms at the interface model interface lose charge,while Fe atoms and O atoms receive the transferred charge.The interface contains covalent and ionic bonds,and the covalent bonding is the main factor in forming the interface.?8?The calculation of the defect formation energy for Cr,Ti and Co doping FeAl?110?/NiAl?110?interface shows that these three kinds of atoms are more likely to replace the Al atoms of FeAl side at the interface.The results of the adhesion work show that the low-dose doping of these three elements is not conducive to the interface bonding performance.The calculation of the defect formation energy for Cr,Ti and Co doping FeAl?100?/TiC?100?interface shows that the doping element Cr can displace Fe and Al atoms of FeAl side and Ti atoms of TiC side at the interface.Among them,Al atoms are most easily displaced,followed by Ti atoms,and finally Fe atoms.The doping element Ti can only displace the Al atom at the interface,as does the Co atom.The calculated adhesion work of these three doping structures are all lower than the pure FeAl?100?/TiC?100?interface,indicating that low-dose doping of Cr,Ti and Co is not conducive to the interface.The calculation of the electronic structure shows that the bonding of the interface has a hybrid bonding of ions,metals and covalent properties.