Zhuyu Ye

Influence of Atomic Oxygen Exposure on Friction Behavior of 321 Stainless Steel

Atomic oxygen (AO) exposure testing has been conducted on a 321 stainless steel rolled 1 mm thick sheet to simulate the effect of AO environment on steel in low Earth orbit (LEO). An atomic oxygen exposure facility was employed to carry out AO experiments with the fluence up to ~1021 atom/cm2. The AO exposed specimens were evaluated in air at room temperature using a nanoindenter and a tribological system. The exposed surfaces were analyzed usign XPS technique.

Thermal Oxidized Coating on Surface of Titanium Alloy for Improvement of Tribological Properties in Vacuum

A hardened layer possessing good bonding strength with substrate has been prepared on the surface of aTi-6Al-4V alloy using the process of thermal oxidation followed by vacuum diffusion. The friction and wear tests are performed in vacuum. The results show that the hardened layer, which thickness can reach 180μm, comprises a thin surface oxide layer and an oxygen diffusion zone. After vacuum diffusion at 820°C, it is found that the decrease rate of the hardness becomes slower with increasing the depth within the diffusion layer,resulting from the formation of the Ti3Al phase. The friction coefficient and the wear rate of the thermal oxidation/vacuum diffusion treated Ti-6Al-4V alloy against AISI 52100 steel are efficiently reduced.

DRY SLIDING WEAR OF Ti-6Al-4V ALLOY AT LOWTEMPERATURE IN VACUUM

Tribological properties of Ti-6Al-4V alloy against GCr15 steel at low temperature in vacuum were measured. The worn surfaces of Ti-6Al-4V alloy specimens were examined by a Hitachi S-570 type scanning electron microscope. The debris were analyzed using a D/max-γB XRD spectrometer. The results showed that the wear rate of Ti-6Al-4V alloy in vacuum ranged within 1.3- 12.0 mg·km −1 at low temperature. The wear rate of Ti-6Al-4V alloy increased with increasing the sliding velocity at low temperature in vacuum. The surface temperature increased to about 32 ◦ C for 300 m of sliding distance. It was found that plough characteristics on the worn surface provide information of the ad- hesion wear. Under the low sliding velocity, microcracks formed on the worn surface indicating damage due to low temperature, while no such microcracks were formed under the higher sliding velocity. The XRD analysis showed that the debris contain Fe, implying that the steel disc was wearing off although the original hardness of the steel was higher than that of the Ti-6Al-4V specimen.

Effects of Atomic Oxygen Exposure on Tribological Property of Zirconium Alloy

ZrTiAlV alloy has potential applications in space mechanisms. The change of wear and the friction coefficient of the ZrTiAlV alloy subjected to atomic oxygen (AO) exposure were investigated aiming to evaluate the tribological properties influenced by the atomic oxygen (AO) environment of the low Earth orbit (LEO). The AO testing employing a 5 eV AO beam was performed under various AO fluencies. The mass loss and roughness of the exposed to AO surfaces were measured. The exposed surfaces and the worn surfaces were analyzed using scanning electron microscopy (SEM) and X-ray photoelectron spectrometry (XPS) to explore the mechanism of AO effect.

Study on Friction and Wear Properties in Vacuum for γ-Ray Irradiated PTFE Coatings

The friction and wear properties in vacuum for the γ‐ray irradiated PTFE coatings were measured. The effects of radiation dose, sliding velocity and load on the friction coefficient and wear loss of PTFE coatings were studied. The worn surfaces were analyzed using scanning electron microscopy (SEM). The results show that the friction coefficient decreased after γ‐ray irradiation and varied little with the irradiation dose. The friction coefficient firstly increased and then decreased with increasing sliding velocity, while it firstly decreased and then increased with increasing load. The wear loss rises after γ‐ray irradiation and decreases with increasing the irradiation dose if the irradiation dose is less than 107 rad. When the irradiation dose reaches 107 rad, the wear loss is lower than that of pristine, not irradiated coating. The wear loss is firstly decreased and then slightly increased with increasing velocity and load under the irradiation dose of 107 rad. It is shown by SEM that there are crack...

Study of Tribological Properties of MoS2+Graphite Sputtered Composite Coatings under various Environment Pressures

MoS2+Graphite composite coatings were synthesized onto 2024 aluminum alloy substrates by sputtering. The friction and wear test were performed at different environment pressures in vacuum using a ball‐on‐disk tribometer. The worn surface of the coating was examined by scanning electron microscopy (SEM). The results show that the friction coefficients and wear rate are increasing with increased environment pressure. A second surface layer was formed on the worn surface, that is harder than the original surface. The hardness of this second surface layer is decreased with increasing environment pressure.

Effect of Gamma Irradiation on Friction and Wear Behavior of MoS2/Graphite Coatings in Vacuum

MoS2 based coatings with graphite were bonded on an Al substrate. the effect of gamma irradiation on the friction and wear properties of MoS2/graphite coatings in vaccum is studied under various sliding velocities and normal loads. X-ray diffraction (XRD) was employed to determine the phase structure of the coatings. Scanning electron microscopy (SEM) was used to examine the morphology of the worn surface before and after the gamma irradiation. The friction test results show that the average friction coefficient of the unirradiated and irradiated MoS2/graphite coatings against GCr15 steel is decreased with increasing sliding velocity and normal load in vacuum. The average friction coefficient has little changes with irradiation. The wear test results show that the wear rates of the unirradiated and the irradiated MoS2/graphite coatings are increased with increasing both of sliding velocity and normal load in vacuum. After sliding in vacuum, the worn surface morphology of the unirradiated and the irradiated MoS2/graphite coatings has the similar characteristics of failure and adhesion. The above results show that the gamma irradiation has limited effect on the friction and wear properties of the MoS2/graphite coatings in vacuum.