An international round-robin experiment to evaluate the consistency of nanoindentation hardness measurements of thin films

We conducted an international round-robin experiment to determine the consistency of nanoindentation hardness measurements of thin films among six different laboratories, using three different samples. These samples were chosen to present a challenge of indenting at small loads (μN range). They were: 250-nm-thick TiNx, 700-nm-thick TiC, and 500-nm-thick TiB2/TiC multilayer coatings (each layer being 3-nm thick), prepared at Northwestern University using magnetron sputtering on silicon (0 0 1) substrates. Each research team was free to use whatever nanoindentor and analysis methods at its disposal. This round-robin experiment demonstrates that for the hardness range of interest (15–35 GPa) and using well-documented procedures and analysis methods, the reported results from all laboratories are essentially the same, allowing for a statistical spread of approximately ±14%. For consistent hardness measurements, four precautions must be observed: (i) proper tip-area function calibration, (ii) using sharp indenters, (iii) performing nanoindentation measurements with minimal thermal drift and with drift correction, (iv) using smooth samples, and (v) measuring the full hardness–maximum penetration curve.