2.4.1. Ball Burnishing

Ball burnishing is a finishing operation based on the plastic deformation of a workpiece's surface via the application of a hard, highly polished ball subjected to a constant external force. Ball burnishing of Ultem specimens was conducted with a burnishing tool designed to be coupled to a CNC milling machine. This tool has an innerspring, the stiffness of which determines the range of ball burnishing forces exerted by a 10 mm chrome-hardened steel ball. The process was made following the procedure described in a previous publication [43] using the optimal configuration of a force of 400 N, 10 passes of the tool, a lateral path width of 0.32 mm, and a forward speed of 2000 mm·min<sup>−</sup>1. Samples were ball burnished on the top side.

#### 2.4.2. Abrasive Shot Blasting

Shot blasting is a cold surface treatment that involves projecting beads on the workpiece to change its surface state, causing plastic deformation to prepare the surface for subsequent processes such as applying a coating layer. In the present study, shot blasting was performed in a manually operated pressure-controlled sandblasting cabinet. The working pressure was set at 5 bar, and samples were individually blasted for 10 to 20 s, using either a mix of spherical glass beads (100 to 850 μm) or white corundum (220 to 36 FEPA (Federation of European Producers of Abrasives) grit, or about 53 to 500 μm). The angle of incidence was kept between 75◦ and 90◦.
