Study On Behavior And Mechanism Of Long Range Effect Of Ion Irradiation On Diffusion

The rapid development of non linear science make it one frontier field of many subjects. Soliton, an important branch of non linear science, pioneered the new ways of mathematical physics and is applicable in many fields of engineering. In crystal lattice, because of the coupling between non linear atomic force and the discreteness of the lattice, the vibrational mode may be localized and the energy transmission became soliton like. It can be predicted this effect will influence barious kinds of material behavior such as diffusion, phase transition and etc..Ion irradiation was employed in this work to excite the crystal lattice vibrational soliton, and the ion energy and current density were adjusted to control the strength of the crystal lattice vibrational soliton. The long range effect of crystal lattice vibrational soliton on the interstitial diffusion, substitutional diffusion and surface segregation were studied. The effects of temperature and grain boundaries in the irradiation-diffusion process were studied, too. The irradiation induced defects and crystal lattice vibrational soliton was separated by diffusion far away from the irradiated surface since crystal lattice vibrational soliton is long range effect while defect is short range effect.45 steel with 200?m columnar decarburized layer was heated at duplex zone with and without ion irradiation. The experiment result revealed carbon diffusion preferentially along the grain boundaries to the surface when the decarburized 45 steel was annealed at duplex temperature, which led to higher carbon concentration at the grain boundaries between columnar Ferrite crystals and then the nucleation of Austenite and their growth into the grain inner. The carbon diffusion was inhibited when ion irradiation was performed. Higher ion energy or ion current density led to stronger inhibition. The longer affected zone than that in classical theory of ion irradiation was explained by non linear crystal lattice excitation, which led to the stronger atomic force. The crystal lattice soliton deformed the shape of the octahedron interstitial in austenite, which led to the increasement of the diffusion activation energy, then the inhibition of carbon diffusion.Polycrystalline copper and directional solidificated single crystal and columnar crystal copper disks were employed as one side of the diffusion couple, the other side was nickel film by magnetron sputtering for its infinite solubility in copper. The diffusion couples were annealed with ion irradiation at the rare face of nickel films. Glow Discharge Optical Emission Spectroscope, Scanning Electron Microscope and Positron Annihilation were employed to analysis the element concentration depth distribution, the microstructure and the defect state of the diffusion couples, respectively. The experiment result revealed an acceleration of Ni diffusion in copper by ion irradiation in single and columnar copper substrate couples. The diffusion coefficient increased while the sample thickness decreased or the ion energy increased. There was no effect of ion current density on the diffusion coefficient. The diffusion activation energy was decreased from 1.01eV to 0.94eV and the frequency factor was decreased from 3.48×10^-7cm²/s to 2.34×10^-7cm²/s in single crystal copper substrate couples. Recrystallization acceleration of columnar crystal copper by ion irradiation led to the abnormal increasement of diffusion coefficient. No effect of ion irradiation on diffusion was found in polycrystalline copper substrate couples. Diffusion led to the disappearance of the interface between copper and nickel, and the appearance of holes in copper substrate, indicating faster copper diffusion into nickel. Slow positron Doppler Broadening Spectroscopy showed the decrease of vacancy like defects at the subsurface of the non irradiated surface. The mechanisms of acceleration of substitutional diffusion were proposed. The long range effect is due to the decrease of vacancy migration energy because of the non linear lattice excitation, but not the diffusion of irradiation damage induced defect to the backside of the samples.Copper segregation at the surface of nickel film were found in the copper-nickel diffusion experiments. Based on the changed surface defect state of single crystal copper after ion irradiation, the mechanism of copper surface segregation was proposed as, the lower vacancy migration energy and the higher probability of vacancy migrating to the surface led to the higher flux of vacancy to the surface vacancy sink. Particularly in copper-nickel system, there is coupling between vacancy flux and copper flux. The copper flux is opposite to the vacancy flux. As a result, the accelerated migration of vacancy to the surface led to the equilibrium segregated surface copper migrated to the subsurface layer.