## 3 Results  
### Coefficient of Friction  
Figure 2 shows the development of the COF as a function of sliding distance under dry and lubricated sliding wear conditions. The sliding distance for all tests was 2000 m. Only the data for a sliding distance up to 500 m are presented, as very little variability in the COF above 500 m was observed. The COF vs. sliding distance curves show three clear regions. There is the initial sharp increase in the COF in the first 50 m. This occurs because the initial contact area is small and increases rapidly as the track is continuously worn, resulting in the first indents and grooves on the wear track. As sliding distance increases beyond 50 m to 200 m, the grooves become more pronounced on the wear track. Both the static partner and the syntactic foam sample are continuously worn, leading to a decrease in the slope of the curve. Beyond 200 m, the contact area becomes nearly constant, and the surface is worn steadily, leading to the flattening and levelling of the COF. The average values of the COF for the S-ASF, M-ASF and L-ASF samples (containing non-heated powder, heated powder and with T6 treatment), together with the ESF sample, are listed in Table 2. It is shown that the COF increases with increasing ASW particle size.  
Figure 2: COF development for ASF and ESF (**a1,a2**), H-ASF (**b1,b2**) and ASF-T6 (**c1,c2**) samples under dry (**a1,b1,c1**) and lubricated (**a2,b2,c2**) sliding wear conditions.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**COF**} & \multicolumn{2}{c}{**Track Depth (mm)**} & \multicolumn{2}{c}{**Track Width (mm)**} & \multicolumn{2}{c}{\(\Delta\)**BR\({}_{\bullet}\)(\(\times\)10\({}^{-3}\)) (mm)**} & \multicolumn{2}{c}{\(\Delta\)**BR\({}_{\bullet}\)(\(\times\)10\({}^{-3}\)) (mm)**} & \multicolumn{2}{c}{
\begin{tabular}{c} **Weight Loss** \\ **(mm\({}^{3}\) m\({}^{-1}\))** \\ \end{tabular} } \\ \hline
**Sample ID** & \begin{tabular}{c} **Dzy** \\ (\(\pm\)7\%)** \\ \end{tabular} & \begin{tabular}{c} **Wet** \\ (\(\pm\)10\%)** \\ \end{tabular} & \begin{tabular}{c} **(\(\pm\)2\%)** \\ \end{tabular} & \begin{tabular}{c} **Wet** \\ (\(\pm\)12\%)** \\ \end{tabular} & \begin{tabular}{c} **(\(\pm\)10\%)** \\ \end{tabular} & \begin{tabular}{c} **Dzy** \\ (\(\pm\)10\%)** \\ \end{tabular} & \begin{tabular}{c} **Wet** \\ (\(\pm\)10\%)** \\ \end{tabular} & \begin{tabular}{c} **Dzy** \\ (\(\pm\)8\%)** \\ \end{tabular} & \begin{tabular}{c} **Wet** \\ (\(\pm\)9\%)** \\ \end{tabular} & \begin{tabular}{c} **Wet** \\ (\(\pm\)3\%)** \\ \end{tabular} & \begin{tabular}{c} **Wet** \\ (\(\pm\)7\%)** \\ \end{tabular} & \
\begin{tabular}{c} **Wet** \\ (\(\pm\)10\%)** \\ \end{tabular} &
\begin{tabular}{c} **Wet** \\ (\(\pm\)12\%)** \\ \end{tabular} \\ \hline S-ASF & 0.19 & 0.07 & 0.058–0.118 & 0.018–0.037 & 5.34 & 2.48 & 28.85 & 8.78 & 78.55 & 12.56 & 0.06 & 0.014 & 0.014 & 0.026 \\ \hline SH-ASF & 0.18 & 0.05 & 0.050–0.111 & 0.001–0.041 & 5.54 & 2.4 & 30.1 & 8.68 & 77.74 & 14.93 & 0.07 & 0.014 & 0.017 & 0.0023 \\ \hline S-ASF-T6 & 0.06 & 0.015 & 0.048–0.115 & 0.018–0.045 & 5.3 & 2.06 & 15.22 & 12.22 & 25.2 & 15.52 & 0.03 & 0.005 & 0.006 & 0.0009 \\ \hline M-ASF & 0.39 & 0.05 & 0.061–0.125 & 0.012–0.034 & 5.7 & 2.86 & 23.54 & 2.74 & 68.08 & 12.53 & 0.06 & 0.010 & 0.015 & 0.0018 \\ \hline MH-ASF & 0.41 & 0.04 & 0.054–0.159 & 0.002–0.016 & 5.86 & 2.8 & 22.1 & 1.1 & 72.65 & 11.74 & 0.07 & 0.008 & 0.02 & 0.0016 \\ \hline M-ASF-T6 & 0.09 & 0.012 & 0.035–0.164 & 0.012–0.034 & 5.6 & 3.12 & 8.45 & 4.87 & 19.53 & 5.25 & 0.04 & 0.004 & 0.008 & 0.0005 \\ \hline L-ASF & 0.48 & 0.04 & 0.143–0.161 & 0.001–0.045 & 5.84 & 3.36 & 19.57 & 1.92 & 52.52 & 4.94 & 0.08 & 0.006 & 0.02 & 0.0011 \\ \hline LH-ASF & 0.06 & 0.02 & 0.027–0.092 & 0.004–0.005 & 6.0 & 2.4 & 8.97 & 1.07 & 13.41 & 1.01 & 0.1 & 0.003 & 0.008 & 0.0002 \\ \hline L-ASF-T6 & 0.1 & 0.01 & 0.055–0.177 & 0.005–0.025 & 5.94 & 5.04 & 2.02 & 1.25 & 15 & 2.25 & 0.0