Stability Research Of Nanocomposite In Binary Immiscible Alloy Systems

In this thesis,the growth behavior of secondary phase Pb with different volume fractions in Al-Pb nanocomposite alloys and the growth behavior of paramagnetic secondary phase C u,paramagnetic matrix phase Ag and ferromagnetic matrix phase Fe in Ag-Cu and Fe-Cu nanocomposite alloys under the combined action of temperature field and magnetic field were investigated by X-ray diffraction(XRD),scanning electron microscopy(SEM),and transmission electron microscopy(TEM).In this thesis,a comprehensive review o f the thermal stability of nanocomposite alloys was carried out.In particular,the thesis introduces the stability of single phase system and nanocomposite alloys under temperature field.In addition,the research progress of the thermal stability of nanocrystalline materials under the combined temperature and external fields was introduced.The coarsening of Pb phase with different volume fractions in Al-Pb nanocomposite alloys follows the coarsening law of secondary phase in conventional grain sized composite alloys,that is,the cubic of the average particle radius of Pb phase grows proportional with the annealing time.The coarsening rate of Pb phase increases distinctly as the volume fraction increases,the variation of coarsening rate is greater than the modern Ostwald ripening theoretical prediction in this composition range.The activation energies for coarsening of Pb phase with different volume fractions do not vary with alloy composition and close to the activation energy of grain boundary self-diffusion of solvent matrix Al.In nanocomposite alloys,the solute atoms diffuse along the grain boundaries of the solvent matrix and high grain boundary fraction of nanophase matrix promotes the diffusion process.The growth of secondary phase C u in Ag-Cu and Fe-Cu nanocomposite alloys under the temperature field can still be described by the cubic growth law and the growth of matrix phase follows the kinetic equation describing the grain growth of pure nanocrystalline metals.The growth of secondary phase and matrix phase is governed by grain boundary self-diffusion.The growth law and the activation energy of secondary phase and matrix phase in nanocomposite alloys do not change under the combined action of temperature field and magnetic field,but the growth rate of secondary phase and matrix phase increases.It means that the applied magnetic field promotes the growth of secondary phase and matrix phase,which is related to the magnetic drive force of the applied magnetic field.