Z.B. Cai

Torsional Fretting Wear Behavior of Bonded MoS2 Solid Lubricant Coatings

The effects of applying a bonded MoS2 solid lubricant to a 1050 steel substrate were investigated using a torsional fretting wear apparatus. Tests were conducted under a normal load of 50 N with angular displacement amplitudes ranging from 0.1 to 5°. Wear scars were examined using scanning electron microscopy, energy-dispersive X-ray spectrometry, optical microscopy, and surface profilometry. The MoS2 coating exhibited different torsional fretting regimes than those of the substrate. Fretting regimes of the coating were primarily in the partial slip regime (PSR) and the slip regime (SR) with no mixed fretting regime. The width of the PSR narrowed. Due to the lubricating effects of the coating, the friction torque was consistently lower than that of the substrate. The damage to the coating in the PSR was very slight, and its granular structure remained even after 1,000 cycles. The damage mechanism to the SR coating was a combination of abrasive wear, oxidative wear, and delamination. The MoS2 coating had potential to alleviate torsional fretting wear.

Friction and wear properties of high-velocity oxygen fuel sprayed WC-17Co coating under rotational fretting conditions

Rotational fretting which exist in many engineering applications has incurred enormous economic loss. Thus, accessible methods are urgently needed to alleviate or eliminate damage by rotational fretting. Surface engineering is an effective approach that is successfully adopted to enhance the ability of components to resist the fretting damage. In this paper, using a high-velocity oxygen fuel sprayed (HVOF) technique WC-17Co coating is deposited on an LZ50 steel surface to study its properties through Vickers hardness testing, scanning electric microscope (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffractrometry (XRD). Rotational fretting wear tests are conducted under normal load varied from 10 N to 50 N, and angular displacement amplitudes vary from 0.125° to 1°. Wear scars are examined using SEM, EDX, optical microscopy (OM), and surface topography. The experimental results reveal that the WC-17Co coating adjusted the boundary between the partial slip regime (PSR) and the slip regime (SR) to the direction of smaller amplitude displacement. As a result, the coefficients of friction are consistently lower than the substrate’s coefficients of friction both in the PSR and SR. The damage to the coating in the PSR is very slight. In the SR, the coating exhibits higher debris removal efficiency and load-carrying capacity. The bulge is not found for the coating due to the coating’s higher hardness to restrain plastic flow. This research could provide experimental bases for promoting industrial application of WC-17Co coating in prevention of rotational fretting wear.

Torsional Fretting Behaviors of UHMWPE against Different Counter-Bodies

In this study, the torsional fretting behaviors of ultra-high molecular weight polyethylene (UHMWPE) against Al2O3 femoral ceramic head ball and medical TC4 titanium alloy ball (both with a diameter of 28 mm) were investigated on a new torsional fretting tester. Angular displacement amplitudes were varied from 0.2° to 90° with a constant rotating velocity of 0.2 °/s, and the numbers of cycles varied from 1 to 103. The kinetics behaviors of the UHMWPE were characterized by using the frictional torque-angular displacement (T-θ) curves. The wear morphologies and damage mechanisms of UHMWPE were studied based on examinations of scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). It was found that the torsional contact stiffness and friction dissipated energy initially rose and then reached steady-state gradually. Sticking was appeared at the centre zone of all fretting scars. Detachment of particles, radial ripples, micro-cracks and ploughs were observed with a higher displacement amplitude value. The physical model of torsional fretting wear was built up.