Magnetism Study Of Carbide Under High Magnetic Field

The service life of heat-resistant steel under medium-high temperature depends on the stability of alloy carbide.In the present work,the magnetic properties of alloy carbides?Fe,Mo?₃C,?Fe,W?₆C and?Fe,Si?₆C at 0K and 0Pa from first principles were calculated.The change of chemical free energy with temperature of alloy carbides?Fe,Mo?₃C and?Fe,W?₆C by MTDATA was obtained.The changes of magnetization and magnetic free energy with temperature of alloy carbide?Fe,Mo?₃C,?Fe,W?₆C and?Fe,Si?₆C under 12T strong magnetic field were calculated according to Weiss molecular-field theory.The conclusions are as follows:1.Fe atoms at different Wyckoff positions make contributions to the magnetic moments of alloy carbides?Fe,Mo?₃C,?Fe,W?₆C,?Fe,Si?6C at 0K and 0Pa.The influence of Fe atom at 8d on magnetic moment is greater than that at 4c for the carbide?Fe,Mo?₃C.Fe atoms at 48f make the major contribution to magnetic moment of?Fe,W?₆C and?Fe,Si?₆C.When Mo,W and Si elements replace the 8d and 4c position of alloy carbides?Fe,Mo?₃C,the 16d,32e and 48f position of?Fe,W?₆C and?Fe,Si?₆C,the magnetic moment of alloy carbides will be reduced.2.At 0K and 0Pa,the formation energy of Fe₂MoC and Mo₃C in alloy carbides?Fe,Mo?₃C is negative;the formation energy of Fe₃W₃C?W at 48f?and Fe₂W₄C in alloy carbides?Fe,W?₆C is negative;and the formation energy of Fe₄Si₂C and Fe₅SiC in alloy carbide?Fe,Si?₆C is negative.It is shown that Fe₂MoC,Mo₃C,Fe₃W₃C?W at 48f?,Fe₂W₄C,Fe₄Si₂C and Fe₅SiC are thermodynamically stable structures.3.The change of chemical free energy with temperature of alloy carbides?Fe,Mo?3C and?Fe,W?6C generally decreased firstly and then increased.At the same temperature,the higher content of Mo or W atom corresponds to the smaller the change of chemical free energy of alloy carbides.4.The change of magnetic free energy with temperature under 12T strong magnetic field of alloy carbide?Fe,Mo?₃C,?Fe,W?₆C and?Fe,Si?₆C presents an increasing trendency.The order of magnetic free energy of alloy carbide?Fe,Mo?₃C:FeMo₂C>Fe₂MoC>Fe₃C.The order of magnetic free energy of alloy carbide?Fe,W?₆C:Fe₂W₄C>Fe₃W₃C?W at 48f?>FeW₅C>Fe₄W₂C>Fe₃W₃C-2?Fe at 48f?>Fe₅WC>Fe₆C.The order of magnetic free energy of alloy carbide?Fe,Si?₆C:Fe₆C>Fe₅SiC>Fe₃Si₃C?Si at 48f?>Fe₄Si₂C>Fe₃Si₃C-2?Fe at 48f?>FeSi₅C>Fe₂SiC.