# Wear Characteristics of Metallic Counterparts under Elliptical-Locus Ultrasonic Vibration
## 3 Results  
### Surface Characteristics  
#### 3.1.1 Surface Roughness  
Surface roughness of sliders is characterized using the stylus method. Among the various surface roughness parameters, \(R_{d}\) is a comprehensive index of surface roughness due to plastic deformation, fracture mechanisms, adhesion and transfer, and surface oxidation. Chaotic changes in surface roughness create a difficult task, in verifying the mode(s) of strength failure and material loss. \(R_{p}\) indicates the maximum height of the asperities, mainly related to the protuberance of the plastic deformation and plowing component. Similarly, dimensions of valleys and hollows, induced by plastic deformation and wear loss result from micro grinding and micro cutting mechanisms, are characterized by \(R_{p}\). Representative parameters of surface roughness of metallic sliders before and after wear are shown in Table 3.  
Surface roughness values for the sliders made of different metals are reduced after wear. The surface roughness \(R_{d}\) of the 45 steel slider turns into a \(R_{d}\) of 0.336 \(\upmu\)m. Compared to the initial  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Parameter** & \(R_{d}\)/\(\upmu\)m & \(R_{p}\)/\(\upmu\)m & \(R_{p}\)/\(\upmu\)m & \(R_{g}\)/\(\upmu\)m \\ \hline
**Slider** & **Initial** & **Wear** & **Initial** & **Wear** & **Initial** & **Wear** & **Initial** & **Wear** \\ \hline
45 \({}^{\#1}\) & 0.64 & 0.34 & 2.34 & 1.34 & \(-\)2.67 & \(-\)2.17 & 18.9 & 37.4 \\
45 \({}^{\#2}\) & 0.81 & 0.46 & 4.12 & 1.27 & \(-\)4.25 & \(-\)3.72 & 18.7 & 25.3 \\
7075 & 0.79 & 0.71 & 3.18 & 1.64 & \(-\)3.65 & \(-\)5.05 & 18.3 & 20.7 \\ Q345B & 0.83 & 0.34 & 3.39 & 1.61 & \(-\)4.71 & \(-\)1.82 & 17.2 & 34.5 \\ QT700 & 0.64 & 0.20 & 3.61 & 0.75 & \(-\)3.78 & \(-\)1.61 & 19.3 & 48.2 \\ \hline \hline \end{tabular} \({}^{\#1}\) Common steel; \({}^{\#2}\) quenched steel. For all surface roughness tests the evaluation length was 0.8 mm and the sampling length was 4 mm.  
\end{table}
Table 3: Changes in surface roughness of metallic sliders surfaces after wear.  
state (\(R_{a}=0.64\)\(\upmu\)m), surface roughness decreased by 47.5% after wear (100 m). For the purpose of evaluating the wear resistance of different metal sliders, a variable quantity of surface roughness in the unit wear length (1 m) was adopted here. Wear resistance of the unit wear length for 45 steel slider \(R_{a}\) decreased by 0.47%, and \(R_{p}\) decreased by 0.18%. Compared to an ordinary 45 steel slider, the 45 steel slider after quenching showed a higher value of surface hardness. Surface roughness of the slider of quenched 45 steel was still high after milling machining. After wear test (400 m) surface roughness \(R_{a}\) of the quenched 45 steel slider dropped by 0.11%, its \(R_{p}\) dropped 0.17%, and its \(R_{p}\) dropped 0.03% for unit wear length.  
For 7075 duralumin alloy sliders, surface roughness showed larger changes for unit wear length, where \(R_{a}\) decreased by 0.11% and \(R_{p}\) decreased by 2.22%, but \(R_{p}\) increased 2%. Following with the slight decrease in surface roughness of the 7075 slider, the distribution density of the asperities (as evidenced by \(R_{s}\)) was slightly reduced too. After a 160 m wear length, the surface roughness parameters of the Q345B slider also underwent considerable changes. In unit wear length, surface roughness \(R_{a}\) was reduced by 0.37%, and \(R_{p}\) and \(R_{p}\) were reduced by 0.33% and 0.38%, respectively. Surface roughness of the ductile iron slider underwent considerable changes after wear of 2830 m. Similarly, in the unit wear length, all three surface roughness values, \(R_{a}\), \(R_{p}\), and \(R_{p}\), were reduced by about 0.02%. As shown above, the value of \(R_{s}\) changed from 19.3 \(\upmu\)m to 48.2 \(\upmu\)m, indicating that the distribution density of asperities of the nodular iron surface fell. Changes in these parameters of surface roughness demonstrate wear resistance and wear mechanisms of different metal sliders in contact with dural alloy 2A12 driving tips.