2.4.1. Microhardness Tests

Vickers hardness was chosen as a measure of strength and investigated for all samples by an MHT-4 Micro Indentation Tester (ANTON PAAR, Graz, Austria), by applying a load of 0.5 N for 10 s. After the indentation, the indents' areas were observed with a Light Microscope AXIOPLAN (ZEISS, Jena, Germany) using 50×/0.75 HD DIC and EPIPLAN 100×/0.75 objectives. The diagonals were measured from images taken with a CCD camera being part of the microscope, as shown in Figure 1. Asymmetries of indents did not affect the lengths of diagonals, and no crack formation occurred. When determining the hardness of an HPT-processed sample, the indents were taken at fixed radii from the center of the specimen, in order to ensure comparability of the results. At least 10 indents per sample state were evaluated.

**Figure 1.** An image of an indentation taken with a CCD camera, with d1 and d2 as the measured diagonals of the indentation. They amount to approximately 25 μm.

For the measurements of Young's modulus, a microindentation tester MHT-3 (ANTON PAAR, Graz, Austria) was used.
