MoDTC/ZDDP tribofilms

Mechanism of Friction Reduction by MoDTC/ ZDDP Tribofilms and Associated Nanometer-Scale Controlling Factors... 

FIGURE 9.6 Nanoscratch data of the MoDTC/ZDDP tribofilm at a constant normal force of 1000 iN. (a) Normal force vs. time and scratch displacement vs. time, (b) lateral force vs. time and normal displacement vs. time, and (c) friction coefficient vs. time and in situ AFM image of the residual scratch groove. 

FIGURE 9.12 AFM height and phase images of the MoDTC/ZDDP tribofilm obtained under light and hard tapping conditions (A) height and (C) phase at = 660 mV and A(/Af =... 

FIGURE 9.13 AFM height and phase line seans of the MoDTC/ZDDP tribofilm at the see-tions indicated in fig. 9.12. 

For the pnrpose of investigating the mechanical properties of the nanostrips in more detail, the tip-sample interaction force was adjusted by further increasing Aq, causing the snrface material of the MoDTC/ZDDP tribofilm to change from elastic to... 

FIGURE 9.16 AFM height and phase images of the MoDTC/ZDDP tribofilm when was increased from 660 mV to 900 mV and then decreased to 850 mV at constant i4, = 0.95. The arrows from 1-T to 5-5 indicate the line scans in fig. 9.17. 

FIGURE 9.19 XPS spectrum of Mo3d from the MoDTC/ZDDP tribofilms. 

FIGURE 9.20 Model of the functionally graded structure of the MoDTC/ZDDP tribofilm. A low-friction inner-skin layer formed hy MoSj nanostrips has low yield strength and acts as a lamellar solid lubricant in lowering the friction coefficient of the MoDTC/ZDDP tribofilm. High concentrations of Ca, O, P, and S oil additive elements in the middle layer decreased and disappeared from the base layer, while the Fe concentration increased from an ultralow level in the surface layer to the same level as the steel disk at the tribofihn-disk interface. 

Consequently, the nanometer-scale measuranents demonstrated that the MoDTC/ZDDP triboflhn possessed a lower shear strength near the surface than the ZDDP tribofilm. The MoDTC/ZDDP tribofilm had an inner-skin layer just below the tribofilm surface at a depth from a few nanometers to around 10 nm. The inner-skin layer was composed of M0S2 nanostrips, which were oriented in the sliding direction and possessed a lower shear strength. 

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