Theory Prediction Of Interface Characteristics Of VC/α-Fe And VN/α-Fe In Steel

In the thesis, the relationship of electronic structure and stability of VC/α-Fe andVN/α-Fe interfaces on the atomic scale system have studied by using the first principlesmethod. Through the construction of VC, VN and α-Fe crystal, their low-index surfacesand interface structures, we calculate the low-index surface, surface energy and electronicproperties of crystal structure mentioned above, and obtain the most stable surfaces of VC,VN and α-Fe. On the basic, we predict the theoretical results of the structurecharacteristics, electronic properties and energies of the interfaces formed between themost stable surfaces of VC, VN and α-Fe, namely, the VC(100)/α-Fe(110) andVN(100)/α-Fe(110) interface. It is provided the basis for that revealing the physical andchemical nature of evolution rule between carbon nitride and ferrite interface on theatomic level, and further enrich and deepen the theory system of crystal interface. Themain results obtained are as follows:(1) The stability order of VC and VN surfaces is:(100)>(110)>(111), and their (100)surface energy is minimum,1.484and0.942J/m2respectively; while the surfaces (111)are the most unstable, and their minimum surface energy values are11.495and10.473J/m2, respectively,which are more higher than their (100) surface energy. The stabilityorder of (110),(100) and (111) surfaces of α-Fe is:(110)>(100)>(111), their surfaceenergy are2.891J/m2,3.084J/m2and3.116J/m2, respectively.(2) The (100) and (110) of VC (VN) are non-polar covalent surfaces, due tosignificant V d-C p or V d-N p interaction, while the (111) is polar surface of metallic. TheFe atomic magnetic moments in (110),(100) and (111) surfaces of α-Fe are respectively2.652μB/atom,2.697μB/atom and2.674μB/atom, more than in α-Fe crystal increased.(3) In VC/α-Fe and VN/α-Fe interface structures, with different VC (100) and VN(100) atomic layers, optimized average atomic spacing decrease. Closer to the interfacelayer, Fe atoms produced delocalization degree is bigger, and formed Fe-C (or Fe-N)covalent bond is stronger. Fe atomic magnetic moment changes after formed interface, in1-ML,3-ML and2-ML interfaces are respectively2.247μB/atom,2.305μB/atom and0.597μB/atom for VC/α-Fe,2.440μB/atom,2.534μB/atom and2.486μB/atom for VN/α-Fe, which all reduced than in Fe(110) surface structure.(4) In VC (VN)/α-Fe interfaces, across the interface have stronger Fe-V metallic orFe-C (Fe-N) covalent bonding existence. The interfacial adhesion of1-ML,2-ML,3-MLVC (VN)/α-Fe interface are2.96(1.47) J/m2,5.14(4.87) J/m2and8.26(3.88) J/m2,respectively. The energy of1-ML interface is most stable with minimum interfacialadhesion.