The innovative impulse excitation technique for high-temperature mechanical spectroscopy

Recent developments in digital signal analysis have allowed substantial progress in the field of impulse excitation techniques (IET), i.e. the mechanical–spectroscopic analysis of `impulse excitedʹ resonant vibrations. The new IET-devices determine several impulse excited resonance frequencies simultaneously. Upon each single impulse excitation, the internal friction corresponding to each of the analysed frequencies is deduced from the exponential decay of the vibration amplitude. In this paper, data obtained with a resonance frequency and damping analyser (RFDA) which is linked to two furnaces, are presented. One of the furnaces can reach temperatures up to 1100°C in air. This furnace was used to characterise phase transformations and point defect relaxations in yttria-stabilised polycrystalline zirconia (Y-TZP) ceramics. Subtle differences in composition affect the measured internal friction spectrum. A second furnace is graphite heated and is used for measurements in inert atmosphere up to 1750°C. In this furnace a sintered silicon nitride was tested to investigate the glass transition and crystallisation of an intergranular amorphous phase.