# Evaluation of the Effectiveness of Surface Defect Removal by Slide Burnishing
## 3 Results and Discussion
### Microhardness  
Microhardness changes as a result of slide burnishing. Microhardness measurements performed on the surface of the workpiece (Figure 11) confirm that the use of a low feed and a high force causes the largest increase in microhardness (for F = 150 N and f = 0.03 mm/rev \(\Delta\)HV0.5 \(\approx\) 89). The obtained maximum value of microhardness on the surface is higher (by about 20 HV) than that obtained in our previous work [23], where oil was used as a lubricant and the force was F = 180 N. Regardless of the burnishing feed, the application of a higher force results in a greater increase in microhardness, with these changes being more visible for f = 0.08 mm/rev. The difference is about 27 HV0.5. The use of a greater force during slide burnishing allows for \"easier\" plastic deformation of the near-surface layers and the disruption of the material's cohesion. This causes an increase in the dislocations' density and their displacement, which leads to an increase in microhardness [19]. On the other hand, the use of a higher feed leads to reduced structural homogeneity due to an increase in the distance between successive tool passes, which, consequently, causes lower microhardness. Figures 12 and 13 show the microhardness distribution as a function of the distance from the surface for samples burnished with variable force F and variable feed f and for ground samples. After pre-treatment (grinding), there is a slight increase in microhardness. The microhardness increase is approximately \(\Delta\)HV0.1 \(\approx\) 20, and the depth of the changes is 5 \(\upmu\)m. A similar microhardness distribution was obtained in our earlier work [23]. In the  
Figure 10: Influence of the technological parameters of slide burnishing thin-walled workpieces on the parameters of the Abbott–Firestone curve. The white bar indicates the surface roughness (parameter Rpk, Rk and Rvk) before slide burnishing. case of the samples burnished with a force of F = 100 N (Figure 12), the thickness of the strengthened layer is about 10 \(\upmu\)m (standard deviation bars do not overlap at this depth). The largest increase in microhardness in relation to the value after grinding occurs just at the surface at a depth of 1 \(\upmu\)m for the sample burnished with F = 100 N and f = 0.03 mm/rev and is \(\Delta\)HV0.1 = 76, while for the sample burnished with F = 100 N and f = 0.08 mm/rev--it occurs at a depth of 3 \(\upmu\)m and amounts to \(\Delta\)HV0.1 = 52. Regarding the samples burnished with a force of F = 150 N (Figure 13), the thickness of the strengthened layer is approximately 15 \(\upmu\)m, regardless of the burnishing feed. The largest microhardness changes for the two burnishing feeds occur at a depth of 1 \(\upmu\)m where \(\Delta\)HV0.1 = 92 for f = 0.03 mm/rev and \(\Delta\)HV0.1 = 82 for f = 0.08 mm/rev. An analysis of the effect of feed depending on the force F shows that the influence of this factor on microhardness is more noticeable during burnishing conducted with F = 100 N, yet it only occurs at a depth of 1 \(\upmu\)m.  
Relating the obtained results to previous studies, it can be concluded that the thickness of the strengthened layer after slide burnishing is similar to that reported in our previous work [23] and that obtained for X19 NiCrMo4 steel [10], and resembles the results obtained after slide burnishing of selective laser melted Ti6 Al4V [14], but lower than that obtained for X6 CrNiTi18 steel [19]. In this study, the degree of hardening from 20% to 38% was obtained, which is a value similar to that reported in [10] but lower than the value obtained after slide burnishing of X6 CrNiTi18 steel [19]. As the burnishing force is increased, more intense plastic deformation occurs due to friction, which translates into higher microhardness and thickness of the strengthened layer. The influence of force F on the obtained effects is similar to the results reported in [12], while the influence of feed is similar to that observed in [14].