*2.2. Laser Peening Treatment*

The LPwC treatment was performed in the Department of Industrial Engineering Laboratories of the University of Bologna (Bologna, Italy). The setup used for the laser shock peening is shown in Figure 3.

**Figure 3.** Setup used for the laser shock peening without coating treatment.

The laser source was provided by a Nd:YAG pulsed laser produced by Quanta Systems (Samarate, Italy). Its settings are as follows: wavelength of 1064 nm, nominal pulse energy of 1.8 J, and a pulse duration equal to 8 ns. The nominal laser power density was 7 GW/cm2.

The peening was applied in the central part of the notch on a rectangular area of 40 × 4 mm2, as shown in Figure 4a. A circular laser spot size of 2 mm in diameter was used, with a distance of 0.25 mm between two adjacent spot-centers. A spot overlapping of 75%, as shown in Figure 4b, was chosen so as to attain complete coverage of the treated area on a single layer, as discussed in the literature [13]. This resulted in a pulse density equal to 1600 pulses/cm2.

**Figure 4.** (**a**) Detailed view of the peened zone. (**b**) The treated area is bounded in the red box.
