Use of the mechanical properties microprobe for characterization of oxide scales

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Abstract
A mechanical properties microprobe (MPM) based on low-load, depth-sensing submicrometre indentation testing is an extremely powerful instrument for examining surface mechanical behaviour and offers several advantages for determining the elastic and plastic properties of protective oxide scales. Its high spatial and force resolutions allow measurements on thin scales and, for thicker surface oxides, determination of gradients in properties. Under optimal conditions, hardness and modulus values can be determined with an overall accuracy of about 10%. A key factor in analysis of the load-displacement data is an accurate determination of the indenter contact area. Because of this, companion indentations into bulk oxides using the same indenter reduce uncertainties associated with comparing the elastic and plastic properties of such materials with their corresponding scales. Use of a standard MPM is currently limited to near room temperature. More effective depth-sensing indentation testing of oxide scales at submicrometre resolution awaits the development of improved specimen preparation techniques, application of advanced analytical methodologies and elevated-temperature operation.