Hardness and modulus measurements on oxide scales

Abstract

This paper provides a comparison between hardness and elastic modulus data measured using a mechanical properties microprobe (MPM), the acoustic microscope and two techniques based on resonant frequency to measure the elastic moduli of oxide systems. Measured values for bulk oxides, namely AI2O3 and Cr2O3, have been used to compare the various measurement systems. The comparison is then extended to measurements on oxide scales. In general, hardness values measured using the MPM technique agree with reported bulk values, although differences between laboratories have been identified which may be attributable to the position of indentation within the scales. Hardness values for scales are found to be similar to hardness values for the bulk, lying in the range 21–30 GPa for A12O3 scales and 18–33 GPa for Cr2O3 scales. Young's moduli for recrystallized AI2O3 have been measured using the mechanical properties microprobe, acoustic microscopy and resonance methods. Data determined using the MPM technique give th...