## 3 Results and Discussion
### Surface Roughness
Large values of the spatial parameter Sal mean that the surface is dominated by low-frequency components, while a small value of Sal is the reverse case. For the base surface, the parameter Sal was 0.021 mm and was clearly lower than in the case of specimens 1-6 (0.2-0.25) and slightly lower than in the case of specimens with the highest feed value 7-9 (0.07-0.08). The developed interfacial area ratio Sdr is defined as the ratio of the increment of the boundary area in the area of definition to the size of the area of definition. This parameter is used as a measure of surface complexity, especially when comparing surface conditions between treatments. In the case of a real flat surface, Sdr = 0, and parameter values less than 1% are characteristic of smoothness finishing treatments, such as honing, lapping, polishing, etc. Burnishing treatment allowed us to obtain Sdr parameter values below 1%, i.e., typical for smoothness treatments. Moreover, values below 0.1% were obtained for specimens for which the force burnishing was \(P=50\) N and \(P=60\) N.  
Another hybrid parameter--the root mean square gradient of the surface Sdq is calculated as the root mean square slope of all points in the defined area. The Sdq of a completely flat surface is 0. This parameter can be, for example, used to evaluate surfaces in sealing applications and to differentiate surfaces with a similar value to the Sa parameter. In the case of the base surface, the value of the Sdq parameter was 0.64, with Sdq = 0.2 for burnished surfaces. The lowest values of the Sdq parameter, similarly to Str, were obtained for specimens for which the force burnishing was \(P=50\) N and \(P=60\) N. Lower values of the Sdq parameter in the case of burnished surfaces indicate a more smooth surface. The bearing area curve (BAC) (Abbott-Firestone curve (AFC)) is a kind of description of the differentiation of surface properties changing with its depth (Figure 8). The curve is divided into parts related to summits, cores, and valleys, thanks to which it is possible to calculate the reduced summit height Spk, the height of the core Sk, the reduced valley depth Svk and two values of the material contribution Smr1 (upper bearing area) and Smr2 (lower bearing area). Large Spk values characterize a surface consisting mostly of high summits providing a small initial contact area and, thus, high contact stress values when the surfaces are in contact. Sk can be used as a measure of the effective roughness depth after the initial running-in period. The Svk parameter, on the other hand, is a measure of the fluid-holding capacity of the sliding surfaces. Surfaces that require good lubrication  
Figure 7: Isotropic rose (**a**) for the base variant and (**b**) after burnishing \(P=60\) N, \(f=1000\) mm/min (experimental run no. 8). should have high Svk values. Spk was lower than Svk in all analyzed cases, including the base specimen. Such a value of peaks leads to minimization of the lapping allowance provided for in operation and may indicate better tribological properties of the surface. On the other hand, increasing the Spk value leads to a decrease in the actual contact area, which may limit the impact of adhesive interactions. Additional data on fluid retention in microgroove valleys at the interface of mating surfaces, valuable for constructors, can be obtained on the basis of vectorization of the microgroove network. The characteristic networks of microgrooves for the base and burnished surfaces are shown in Figure 9. The TalyMap 6.0 software allows us to determine three important parameters: the maximum and average depth of the grooves and their density. The maximum depth of grooves for the base surface, which is 31.5 \(\upmu\)m, is significantly greater than for burnished surfaces (2.84-6.21 \(\upmu\)m). In turn, the density of the grooves after the burnishing process was relatively similar to the density of the grooves after the treatment of the base specimen (212-284 cm/cm\({}^{2}\)).