Measurements of Hardness and Other Mechanical Properties of Hard and Superhard Materials and Coatings

We discuss the methods and problems associated with a reliable measurements of mechanical properties of superhard (H ≥ 40 GPa) and ultrahard (H ≥ 80 GPa) materials and coatings. It is shown that the “nanoindentation” can yield incorrect results of hardness and elastic moduli when applied to super- and ultrahard materials. Therefore, the classical two-step method, where, after the indentation with a given load, the size of remnant indentation is measured by a microscope, is recommended for the verification of the results obtained from the “nanoindentation.” We further discuss methods for the determination of elastic moduli, tensile yield strength, and internal friction. Special attention is devoted to the measurement of the mechanical properties of super- and ultrahard thin films on softer substrates. It is shown that the Buckle’s rule, according to which the indentation depth should not exceed 10 % of the film thickness of a hard film on soft substrate, does not apply for hard and superhard materials.