Thermal and mechanical stability of Mg based nanocomposite studied by internal friction measurements

Magnesium matrix composites show improved wear resistance, enhanced strength and creep resistance in comparison with their monolithic counterparts. On the other hand they keep low density and good machinability. Internal friction measurements are suitable tool to detect changes in the microstructure of thermally or mechanically loaded composites. Samples from pure magnesium reinforced with zirconia nanoparticles were thermally cycled between room temperature and increasing upper temperature of thermal cycle. After thermal cycling amplitude dependence of decrement was measured. Very high values of the logarithmic decrement were ascribed to the poor binding between the matrix and ceramic nanoparticles. The influence of cyclic bending on the damping behaviour of the same nanocomposite was determined at room temperature. Measured decrease of the resonant frequency indicates the stiffness loss as a function of cycling. Observed decrease of amplitude independent component of decrement at the end of the sample life time is due to increase of the dislocation density. These dislocations can be absorbed by the interface. Crack deflection along an interface is followed by the separation of the particle/matrix interface.