Internal friction in microcrystalline magnesium reinforced by alumina particles

Using internal friction measurement, changes in the microstructure of microcrystalline magnesium and magnesium with 3 vol.% of Al2O3 microparticles and nanoparticles, due to thermal treatment, have been investigated. Materials have been thermally treated at increasing temperature and then the amplitude dependence of the logarithmic decrement was measured at room temperature. The thermal treatment influences the amplitude-dependent component of the decrement in composite with nanoparticles while in composite with microparticles no influence has been estimated. Thermal stresses induced in the composites due to a difference between thermal expansion coefficient of matrix and ceramic particles may create new dislocations during the cooling from elevated temperatures. Density of new dislocations depends on the particle size. The thermal stresses can achieve yield stress in the matrix and micro-glide of newly created dislocations as well as their annihilation may occur.