Graphically presented experimental results obtained after data processing by TalyMap Silver 4.1.2 software, showing the effect of applied modifications to the working surface of planer knives on the values of 3D surface roughness parameters, as well as other features of surface morphology such as depths histogram and isotropy, are shown in Figs. 1–3. The obtained measurement results indicate the possibility of reducing the roughness of the working surface of the knives due to the application of anti-wear coatings: multilayer, monolithic, monolithic-gradient and gradient.
Analyzing the chart in Fig. 1a, it can be observed that the application of anti-wear coatings to the working surface of planer knives resulted in a significant reduction in the arithmetical mean height of the surface. In this case, the changes in the mean value of the Sa(av) parameter obtained for the modification of the working surfaces were from 25–41% smaller with respect to the uncoated surface. At the same time, it can be noted that the considered parameter of surface texture took the lowest value in the case of surface modification with monolithic-gradient coating (Sa(av) = 1.45 µm).
Figure 1b shows a chart of the effect of the type of coating used on the maximum height of the surface. The application of anti-wear coatings to the working surface of planer knives resulted in a decrease in the value of the considered parameter of surface texture. The decrease in the value of the St(av) parameter was 28% for multilayer coating, 38% for monolithic coating, 39% for monolithicgradient coating, and 29% for gradient coating, respectively.
Figure 1c presents the effect of the type of antiwear coating applied on the skewness. The results show that the application of the coating to the working surface of the knife causes significant changes in the symmetry of the distribution of ordinates with respect to the mean plane. It should be assumed that on the surface of uncoated knives there are elevations in a sharpened shape, as evidenced by the high positive values of obliquity Ssk(av) = 0.372. In the case of the surface of coated knives, the values of the parameter Ssk(av) were from 76–111% smaller in relation to the surface of uncoated knives, and the smallest value was registered for the multilayer coating (Ssk(av) = -0.042). Such results indicate the presence of plateau-like elevations on the surfaces of coated knives.
The effect of the type of coating used on the density of peaks between specific sections (SPc) is presented in the form of a chart in Fig. 1d. Analyzing the obtained test results, it can be seen that the use of anti-wear coatings resulted in a reduction in the value of the spatial parameter under consideration. The density of peaks between the specified cross sections in the case of the application of the gradient coating was lower by 72%, for the multilayer and monolithic coating it was lower by 84%, and for the monolithic-gradient coating by as much as 92%. At the same time, it can be noted that the considered parameter of surface texture took the lowest value in the case of surface modification with monolithic-gradient coating (SPc(av) = 0.668 pks/mm2).
A chart of the variation of the surface density of the summits of local rises depending on the type of vacuum-plasma modification of the working surfaces of planer knives is shown in Fig. 1e. The application of anti-wear coatings on the working surface of the knives resulted in an increase in the value of the Sds parameter in every case analyzed. The increase in the average value of the Sds(av) parameter was about 10% for monolithic and gradient coatings, and about 14% for multilayer and monolithic-gradient coatings. The presented test results also indicate that the highest density of surface roughness vertices was achieved when the monolithic-gradient coating was used (Sds(av) = 1,270 pks/mm2).
Figure 1f shows the experimental results of the effect of the type of anti-wear coating applied on the texture aspect ratio of the surface. The results obtained show that the spatial (surface) parameter reached the smallest value of Str(av) = 0.0545 for an uncoated surface. Such a small value of the considered parameter is characteristic of anisotropic surfaces. Analyzing the graph, it can also be seen that the application of coatings to the working surfaces of the planer knives increased the value of the parameter of surface texture Str, and thus affected their isotropy. The highest value of the parameter Str(av) = 0.611 was obtained for the monolithic coating. In contrast, the use of gradient, multilayer and monolithic-gradient coating increased the value of texture aspect ratio of the surface to 0.263, 0.464, and 0.568, respectively.
A graphical interpretation of the experimental results, showing the relationship between the type of anti-wear coating applied and the root mean square slope of the surface (Sdq), is shown in Fig. 2a. Analyzing the chart, it can be seen that the application of coatings to the working surface of the planer knives resulted in a decrease in the value of the hybrid (surface) parameter. In the case considered, the changes in the average value of the Sdq(av) parameter obtained for vacuum-plasma modifications of the working surfaces of the knives were from 11–29% smaller with respect to the uncoated surface. The decrease in the value of the considered parameter of surface texture was 11% for monolithic coating, multilayer coating 15%, gradient coating 24% and monolithic-gradient coating 29%, respectively.
Figure 2b shows the results obtained for the hybrid parameter arithmetic mean summit curvature of the surface (Ssc). The results obtained show that the application of a monolithic coating to the working surface of the knives resulted in a reduction in the value of the considered parameter of surface texture to 0.0706 1/µm. The smallest value of the parameter Ssc(av) = 0.0593 1/µm was obtained for the gradient coating. In contrast, the use of multilayer and monolithic-gradient coatings reduced the value of the arithmetic mean sum of curvature of the surface to 0.0675 1/µm and 0.0608 1/µm, respectively.
The results of studies of the effect of the type of vacuum-plasma modification of the working surfaces of knives on the developed interfacial area ratio (Sdr) are shown in Fig. 2c. Analyzing the chart, it can be concluded that the application of anti-wear coatings resulted in a decrease in the value of the Sdr parameter. The presented test results also show that the analyzed hybrid (surface) parameter reached the highest value for the surface with the monolithic coating applied Sdr(av) = 5.86%, while its minimum value was observed for the monolithic-gradient coating Sdr(av) = 3.80%.
Figure 2d shows the results of experimental studies of the effect of anti-wear coatings on the bearing index (Sbi). Analyzing the chart, it can be seen that the application of vacuum-plasma modifications to the working surfaces of knives in three of the four cases considered resulted in an increase in the average value of the Sbi(av) parameter (for the multilayer coating by 8%, for the monolithic coating by 17% and for the gradient coating by 5%). At the same time, the analyzed functional (surface) parameter took the lowest value when the monolithic-gradient coating was used Sbi(av) = 0.230.
The results of the study of the influence of the type of applied modification of the working surface of planer knives on the core fluid retention index (Sci), presented in graphical form (Fig. 2e), indicate the existence of significant correlations. The use of antiwear coatings results in a decrease in the value of the Sci parameter. The results obtained allow to conclude that the lowest fluid retention in the core is characterized by the surface with a multilayer coating applied (Sci(av) = 1.482). In contrast, the application of a monolithic-gradient coating reduced the value of the considered functional (surface) parameter to 1.573, a change of only three percent.
The experimental results of the effect of applied anti-wear coatings on the valley fluid retention index (Svi), presented in graphical form, are shown in Fig. 2f. The application of a multilayer coating on the working surface of the planer blade increased the average value of the Svi(av) parameter by 14%. In addition, analyzing the chart, it can be seen that the application of monolithic, monolithicgradient and gradient coatings caused a decrease in the valley fluid retention index by about 3%. The smallest value of the considered functional (surface) parameter was observed for the uncoated knife surface Svi(av) = 0.112.
Figure 3a shows the features of the surface morphology of a knife coated with a multilayer coating. The application of vacuum-plasma modifications to the working surface of planer knives caused the values of the parameters of the geometric structure of the surface to change significantly. Among other things, a decrease in the values of amplitude parameters can be observed. Analyzing the microtopography of the working surface of a multilayer-coated planer knife, it can be seen that the maximum height of the roughness is 22.1 µm. The value of the Ssk parameter is negative, which indicates that most of the material is localized near the vertices of the surface. The results of the 3D analysis show that the knife surface coated with the antiwear coating shows a higher level of isotropy (isotropy 51.4%) compared to the unmodified surface (Fig. 3e). The morphological rose shows the fundamental directions in which the surface irregularities are arranged: the first direction 178°, the second direction 177° and the third direction 4°. The distribution of ordinates approaches a normal distribution. Less than 80% of the analyzed surface is made up of areas where the height of inequalities is between 0-9.4 µm.
Figure 3b shows the recorded microtopographs and 3D analyses of the work surface of a planer knife coated with a multilayer coating. The analysis of the obtained measurement results indicates that as a result of vacuum-plasma modifications it is possible to achieve a surface roughness expressed by the parameter Sa = 2.01 µm. Analyzing the topography of the working surface of the knife coated with the monolithic coating, it can be seen that the maximum height of the geometric structure of the analyzed surface is more than 23 µm. The polar diagram shown with texture directions (first direction 1.5°, second direction 179° and third direction 176°) indicates that the analyzed knife surface has an isotropic structure (isotropy 58.2%). The depths histogram is a normal distribution with a slight negative skewness. The skewness value of the height distribution is equal to Ssk = -0.116. This indicates that most of the material is localized near the vertices as was the case when the knife working surface was modified with a multilayer coating. 80% of the analyzed surface has areas of roughness height less than 13 µm.
The results of measurements of the working surface of the knife coated with the monolithicgradient coating are shown in Fig. 3c. The values of the topographic parameters indicate that the application of the anti-wear coating to the working surface of the planer knife resulted in a reduction in the height of the irregularity. The height difference occurring between the highest elevation and the maximum depth of the indentation for the analyzed surface roughness is 23.6 µm. The difference of directions (first direction 6°, second direction 175° and third direction 172°) with texture directions presents that this kind of coating generated structure with 61.5% value of isotropy. The depths histogram is close to a normal distribution with a high positive skewness. The skewness value of the height distribution is positive Ssk = 0.410, indicating that most of the material is located near the surface valleys. As much as 80% of the analyzed surface topography consists of areas with a height of inequality not exceeding 15.8 µm.
Figure 3d shows the results of the analysis of changes in the surface morphology of a planer knife after modification with a gradient coating. The application of vacuum-plasma modification of the working surface of the knife caused a reduction in the values of the amplitude parameters of the geometric structure of the surface. Analyzing the topography of the surface, it can be concluded that the maximum height of its roughness is 24.7 µm. Besides, the results of the metrological analysis show that the surface of the gradient-coated knife shows a higher level of anisotropy (isotropies of 4.23%) compared to the unmodified surface – isotropies of 16.0% (Fig. 3e). The direction rose illustrates the main directions of the surface texture: first direction 5.5°, second direction 90° and third direction 170°. The depths histogram is characterized by high clustering and apparent negative skewness. The skewness value of the height distribution is negative Ssk = -0.74, indicating that most of the material is located near the vertices of the surface. Approximately 80% of the analyzed surface consists of areas where the height of inequality is in the range of 0-9.6 µm.