USE OF THE MECHANICAL-PROPERTIES MICROPROBE FOR CHARACTERIZATION OF OXIDE SCALES

A mechanical properties microprobe (MPM) based on low-load, depth-sens ing submicrometre indentation testing is an extremely powerful instrum ent for examining surface mechanical behaviour and offers several adva ntages for determining the elastic and plastic properties of protectiv e oxide scales. Its high spatial and force resolutions allow measureme nts on thin scales and, for thicker surface oxides, determination of g radients 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 deter mination of the indenter contact area. Because of this, companion inde ntations 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 cu rrently limited to near room temperature. More effective depth-sensing indentation testing of oxide scales at submicrometre resolution await s the development of improved specimen preparation techniques, applica tion of advanced analytical methodologies and elevated-temperature ope ration.