Diffusion Behavior Of Carbide Forming Elements (Cr?V?Mo?W) In Pure Iron Under High Magnetic Field

Nuclear fusion power generation is an important technology which is researching during 21st century.Compared with the nuclear fission,thermonuclear fusion is not only easy to obtain resources,but also much safer than nuclear fission reactors.The cladding structure material of nuclear fusion device is low-activated steel,its service environment is high magnetic field and high temperature,and this extreme conditions can significantly affect the service life of the steel.One of the main strengthen ways in steels is precipitation strengthening.of alloy carbides,the growth,coarsening,dissolution or disappearance of precipitation phases can significantly reduce high temperature creep strength.The nucleation and evolution of carbides can not be separated from the diffusion of alloy atoms.Therefore,researching the diffusion behavior of carbide forming elements in different phase regions of pure iron under the combined action of high magnetic field and high temperature has important theoretical significance to improve service life and mechanical property of alloy steels under extreme conditions.In this paper,by means of optical microscope,electronic microprobe analyzer,scanning electronic microscope etc,the solid diffusion behavior of Fe-Cr,Fe-V,Fe-Mo and Fe-W were researched with and without high magnetic field.Boltzmann-Matano plane solution method was used to calculate the diffusion coefficient of the diffusion couple.The results of solid state diffusion behavior of Fe-Cr diffusion couple under high magnetic field show that the high magnetic field suppresses the interdiffusion of Fe and Cr annealing in the austenite phase of pure Fe,decreases diffusion distances and diffusion coefficient of Cr in Fe obviously.Annealing in the paramagnetic ferrite phase and ferromagnetic ferrite phase,strong magnetic field promotes the interdiffusion of Fe and Cr,increases the diffusion distance and diffusion coefficient of Cr atoms in pure iron significantly.Magnetic field has no significant effect on the phase composition of the diffusion layer in the same temperature region.The results of solid state diffusion behavior of Fe-V diffusion couple under high magnetic field show that there is almost no interdiffusion of Fe and V atoms in the three different phase regions.The acceleration effect of magnetic field on the formation of vanadium carbides is more pronounced in the paramagnetic ferrite phase region and the ferromagnetic ferrite phase region.The applied magnetic field did not change the species of vanadium carbide in the diffusion layer of the same phase.The results of solid state diffusion behavior of Fe-Mo diffusion couple under strong magnetic field show that the magnetic field inhibits the inter-diffusion of Fe and Mo atoms in the austenite phase region of Fe and in the paramagnetism ferrite phase region,decreases the diffusion distances and diffusion coefficient of atoms in pure Fe.During paramagnetism ferrite phase zone annealing,there was almost no mutual diffusion of Fe and Mo.In three different phase regions,the applied magnetic field do not significantly change the phase composition of the diffusion layer in the same temperature range.The results of the solid-state diffusion behavior of Fe-W diffusion couple under strong magnetic field show that annealing in the austenite and paramagnetic ferrite region of Fe,magnetic field inhibits the diffusion of Fe and W.decreases the diffusion distance and diffusion coefficient of W atoms in pure Fe obviously.During annealing in the ferromagnetic ferrite phase of Fe,there was almost no mutual diffusion of Fe and W atoms.In three different phase regions,magnetic field did not significantly change the phase composition of the diffusion layer in the same temperature.