The use of depth-sensing submicron indentation testing to characterize the mechanical behavior of thin oxide scales

Abstract

The ability of a metallic material to withstand aggressive oxidizing environments depends not only on the chemical stability and slow growth of a protective surface oxide, but also on the mechanical integrity of the scale. Therefore, a better understanding of the mechanical nature of the most protective oxide scales is being sought based on the premise that properties such as hardness, modulus, and plasticity ultimately determine whether a chemically stable surface oxide will retain its integrity in corrosive, high-temperature environments. To this end, the possible advantages of using low-load, depth-sensing indentation to generate such data are being evaluated. The determination of various mechanical properties of high- temperature oxide scales has been of interest for many years. Methods include traditional microhardness testing frequency damping measurements of elastic properties, and acoustic emission detection of scale cracking. Recently, depth-sensing submicron indentation testing has been used to determine both plastic and elastic properties of oxide scales in an effort to demonstrate that such an approach can be generally applied to surface products that are too sparse or thin for more typical techniques. One particular concern in this case is the relevance of room-temperature measurements for scales whose performance is judged at elevated temperature. Woodmore » and Hodgkiess addressed many of these issues in an excellent manner and their arguments will not be repeated here. However, it is important to note that many of the advantages cited for hardness measurements of oxide scales are even more compelling in view of the recent availability of the means to conduct depth-sensing indentation testing on a micron scale.« less