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Fig. 4. PSD curves calculated from topographies of various machined surfaces measured with a WLI.
Fig. 3. Surface topography measured with an AFM: measurement result for a 10 lm 10 lm area of the electroless-plated NiP cut surface.
values obtained from multiple measurements were consistent with those shown in Figure 1.
Next, the surface topographies within an area of 1 lm 1 lm were measured with the AFM. Figure 2 shows the measurement results, including the surface topographies together with cross-sectional profiles approximately through their centers. The OFC surface had tiny holes, as shown in Figure 2a, whereas the electroplated Cu surface had a sand-textured finish, as shown in Figure 2b. The RMS roughness of the electroplated Cu surface was smaller than that of the OFC surface, that is, 1.72 nm and 2.32 nm, respectively. Compared with these surfaces, the electrolessplated NiP surface was smoother, as shown in Figure 2c. For the electroless-plated NiP surface, the RMS roughness was 1.50 nm. In Figure 2c, small elevations( white dots) are observed scattered on the surface. These are considered to be fine chips generated during turning adhered to the surface. After turning, the surface was only rinsed with an organic solvent using a wash bottle without wiping, in order to preserve the surface morphology as much as possible. As a result, some fine chips likely remained on the machined surface. Thus, although each machined surface exhibited a different surface appearance, the electroplated Cu surface was not as smooth as the electroless-plated NiP surface but was smoother than the OFC surface when uniformly compared in terms of RMS roughness.
Figure 3 shows the AFM measurement result for a 10 lm 10 lm area of the electroless-plated NiP surface machined last. Regular tool marks are observed, and each tool mark exhibits a profile corresponding to the arc of the tool tip. These observations indicate that the original geometry of the cutting edge was almost maintained during the finishing process, suggesting that no significant tool wear or chipping occurred.
In addition, measurements were performed at three different locations near the radial midpoint for each material. The average, maximum, and minimum RMS roughness
Fig. 5. PSD curves calculated from topographies of various machined surfaces measured with an AFM.
were 2.29, 2.32, and 2.27 nm for OFC; 1.74, 1.77, and 1.72 nm for electroplated Cu; and 1.44, 1.50, and 1.36 nm for electroless-plated NiP, respectively. Thus, the relative magnitudes of the average RMS roughness values obtained from multiple measurements were consistent with those shown in Figure 2.
3.2 Power spectral density( PSD) analysis
We performed the PSD analysis of the obtained surface profiles. Figure 4 shows the PSD curves calculated from the surface profiles measured with the WLI. Specifically, the one-dimensional( 1D) PSD curve obtained by WLI was calculated using the software built into the measurement system. The PSD was calculated from a line profile extracted from the center of the measured surface, and the analysis was performed over the full evaluation length of the profile. The PSD curve shown represents the average of three measurements for each material.
As shown in Figure 3, the PSD of the OFC surface tends to be the highest among the three materials, whereas those of the electroplated Cu and electroless-plated NiP surfaces