785680.fig.009a
(a)
785680.fig.009b
(b)
785680.fig.009c
(c)
Figure 9: SEM and EDS analysis of worn surface of steel ball after four-ball test lubricated by the water-added 1.6 vt.% TiO2 nanoparticles. (a) Without ultrasonic washing; (b) with ultrasonic washing for 2 minutes; (c) with ultrasonic washing for 5 minutes.