*2.4. Hardness Measurement*

The hardness measurements were performed in order to quantify the effect of the LPwC treatment on the surface hardness of the treated specimens. The measurements were conducted according to the E10-18 standard test procedure for Brinell hardness [17]. The sample used for testing was taken from the LPwC-treated specimens, and was additionally machined in order to accommodate the hardness testing machine. Five measurements were performed, two in the central, peened section of the specimen (Figure 6), and three on the untreated part of the sample (Figure 7). As the diameter of the indentation (e.g., about 1 mm) is small compared with the radius of the notch, the effect of the curvature was not considered.

**Figure 6.** Central hardness measurement points. The two locations used for the Brinell hardness measurement in the region treated with LPwC are shown.

**Figure 7.** Side hardness measurement points. Locations considered for hardness measurement of the untreated material.
