Plastic and fatigue behaviour of ultrafine-grained magnesium

Ultrafine-grained Mg (UFG-Mg) samples were prepared by milling of powder in an inert atmosphere and subsequent compacted and hot extruded. The linear grain size of the specimens estimated by X-ray line profile analysis was about 100–150 nm. Compression tests were performed at temperatures between room temperature and 300 °C. The yield stress as well as the maximum stress decreases with temperature. This decrease and the steady-state character of the stress–strain curves at elevated temperatures indicate possible contributions of recovery processes. The influence of cyclic bending on the damping behaviour of UFG-Mg was determined at room temperature. The logarithmic decrement of free decaying vibrations of bending beams was determined as a function of the cycle number. Changes in the microstructure are manifested by changes in damping as well as in the resonant frequency. Cracks nucleation and growth in the material was manifested by a rapid increase of damping with increasing number of cycles and finally by failure of the sample.