Nonlinear Diffusion Kinetics Of The Inward Atoms To Nano-scale Multilayers

Due to the nanoscale modulation structure and amounts of interfaces in nanometer-scale multilayers, free energy of the multilayers is consistent with that of the nanometer-scale nonuniform system and the diffusion coefficients of atoms depend strongly on their composition. The nonlinearity of diffusion in the nanometer-scale multilayers is manifested in the change of the range of the validity of the classical diffusion laws and in peculiar concentration distribution and its time evolution. At present, diffusion in nanometer-scale multilayers concentrates on experimental research. In the theoretical study, classical diffusion laws were used to investigate diffusion in the multilayers, however, nonuniformity of nanometer-scale multilayers was ignored. In this paper, nonlinear diffusion kinetics of the inward atoms to nano-scale multilayers was studied. The kinetics equation that meets space-translation symmetry was proposed based on the nonlinear kinetic discrete model. It was found that both mobility and diffusion driving force which are the two main parameters in kinetics equation are the exponential function. The mobility is the exponential function of saddle point energy, and It is a constant in the low concentration region. In the high concentration region, the mobility increases with increasing the temperature whereas decreases with increasing the concentration. The driving force is the difference of exponential function of the neighbor planes' chemical potential, and strongly deviates traditional driving force with increasing the difference of the neighbor planes' chemical potential.Using computer simulation technology to calculate the insterials diffusion processings in multilayers with different wavelength and interface energy state, based on none uniform system nonlinear diffusion theory combined with Hillert sublattice theory. It is found that the diffusion processing was enhanced with the decreasing of the wavelength. And the ablity to store the insterials was also enhanced. The interface energy state dominated the diffusion processing.