Jinfang Peng

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.

Experimental Study on Corrugation of A Sliding Surface Caused By Frictional Self-Excited Vibration

abstract A series of tests is conducted on a pin-on-disc tester to study the effect of frictional self-excited vibration on evolution of the scar profiles. A laser displacement sensor is used to measure the profile size of the worn scars. An accelerometer is used to measure vibration of the pin specimen. The test results show that a sustained frictional self-excited vibration easily occurs under dry friction. When the vibration lasts for a long enough time, corrugation is generated on the sliding surface of the disc specimen. The wavelength of corrugation is approximately equal to the sliding speed multiplied by the period time of the friction-induced vibration.

Experimental Study of the Fretting Wear Behavior of Incoloy 800 Alloy at High Temperature

ABSTRACT The fretting wear behavior of the nuclear power material Incoloy 800 was investigated in this study. A PLINT high-temperature fretting tester was used on an Incoloy 800 cylinder against a 304SS cylinder at vertical cross contact under different temperatures (25, 300, and 400°C). During testing, a normal load of 80 N was applied, and the displacement amplitudes ranged from 2 to 40 µm. The fretting wear mechanism at high temperatures and the kinetic character of the materials of the Incoloy 800 steam generator tube were analyzed. Results showed that the fretting running regimes varied little with ncreasing temperature, and some microcracks were observed in both the mixed fretting regime (MFR) and the partial slip regime (PSR) at high temperatures. Slight abrasive wear and microcracks were the main wear mechanisms of the Incoloy 800 alloy in PSR, whereas those in the MFR and the gross slip regime were oxidative wear, abrasive wear, and delamination.

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.

Antiwear Properties of Bonded MoS2 Solid Lubricant Coating under Dual-Rotary Fretting Conditions

ABSTRACT Bonded MoS2 solid lubricant coatings are widely used in tribology for their friction-reducing and antiwear properties. However, such coatings have been rarely investigated in complex fretting conditions, such as dual-rotary fretting (DRF). DRF is a complex fretting wear mode that combines torsional fretting with rotational fretting. In this work, the antiwear properties of bonded MoS2 solid lubricant coating under dual-rotary fretting conditions were studied. Results indicated that the MoS2 coating had better friction-reducing and antiwear properties than the substrate for alleviating DRF wear. The coating can greatly influence the fretting regimes and reduce the coefficient of friction. Furthermore, the service life of the coating was strongly dependent on the competition of the two fretting components and was reduced as the rotational fretting component increased.

Effect of roughness on electrical contact performance of electronic components

Abstract This study investigated the effects of electrical contact resistance (ECR) on pogo pins used in mobile phones, chargers, digital cameras, Bluetooth headsets, medical equipment, and other electronic products with different surface roughness. Experimental results revealed that metallic wear debris is generated by fretting motion and formation of a third body on rough surfaces without removal by fretting motion, thus increasing ECR. Wear debris does not easily form the third body at contact areas of smooth surfaces and causes formation of metal–metal contact pattern. Results showed low ECR with fretting motion. 3D and 2D profiles of contact area verified the definition of contacting high spots, further explaining increases in ECR.

Experimental study of the fretting wear behavior of Inconel 690 alloy under alternating load conditions

This study investigated the fretting wear behavior of the nuclear power material Inconel 690 alloy. An improved PLINT high-temperature fretting tester was used on an Inconel 690 tube against a 1Cr13 cylinder at different temperatures (25 ℃ and 300 ℃) under alternating load conditions. The fretting-wear mechanism and the kinetic characteristic of Inconel 690 alloy were analyzed. Results showed that the fretting running behavior was closely related to the normal excitation frequency. In parallelogram shaped Ft–D curves, the friction fluctuates periodically, and accordingly the fretting was running in the slip regime. The steady-state friction force at room temperature in air was higher than that at 300 ℃. Moreover, the damage behavior of the fretting for Inconel 690 alloy strongly depended on the normal load, displacement amplitude, temperature, and excitation frequency in atmospheric environment. A superposition effect of fretting wear behavior was discovered because of the combined effect of alternating normal and tangential forces; thus, delamination became more significant. Abrasive wear and delamination were the major mechanisms in Inconel 690 alloy at room temperature in ambient air. The dominant mechanisms at 300 ℃ were the abrasive wear, oxidation wear, and delamination.