Internal Friction and Young's Modulus of 9Al₂O₃ 2B₂O₃ Whisker Reinforced Aluminum Matrix Composite

Anelastic behavior of a 9Al(2)O(3)(.)2B(2)O(3) (AlBw) whisker reinforced aluminum composite has been examined through the measurements of the dynamic Young's modulus and internal friction over a temperature range of 25 to 500 degrees C at frequencies of 0.01, 0.05 and 0.1 Hz. A standard servo-hydraulic mechanical testing machine equipped with an infrared lamp heater was employed, but the dynamic measurement system therein was especially designed by assembling a scanning laser extensometer and a frequency response analyzer for detecting the amplitude and phase lag of strain in response to a sinusoidal time-varying stress. Two peaks of internal friction were observed over the ranges 100 to 250 degrees C (LT peak) and 250 to 400 degrees C (HT peak), together with marked decreases in the dynamic Young's modulus in the same temperature ranges. From a quantitative analysis of the experimental data, it is concluded that the HT peak phenomenon is due to grain-boundary relaxation, whereas the LT peak phenomenon is ascribable to the relaxation caused by stress-directed interfacial diffusion of Al atoms along the whisker-matrix interface.