Performance Deterioration Analysis of the Used Gear Oil

In the present paper, we have investigated the tribological properties and microstructure of the used gear oil theoretically and experimentally. The deterioration process of the in-service gear lubricant oils was also discussed. The viscosity and microstructure of oils running different mileages were analyzed by viscometer and Fourier Transform Infrared Spectroscopy (FTIR), respectively. In addition, the friction and wear behaviors of the friction pair of the GCr15 steel ball and disc were investigated using a ball on disc tribometer under different mileages’ gear oils lubrication conditions. These techniques give reproducible and reliable data with which to evaluate the severity of deterioration process of oils. The objective of this work is to understand the deterioration process of gear oil and analyze the influence of deterioration on the performance and microstructure of lubricant oils used in gear box. Possible explanations of deterioration process as well as its influence on friction and wear behaviors are also discussed. The results reveals the tribological properties of used oils depended on strongly the microstructure and its deterioration process of oil.

Numerical Investigation on Flow Pattern of Air-Oil with Different Viscosities Lubrication

In the present work, the performance of oil-air two-phase flow under different lubricant oils was investigated. The simulation method was applied to study the influence of the oil viscosity on the flow pattern, velocity distribution and Re number in oil-air lubrication by FLUENT software with VOF model to acquire the working performance of oil-air lubrication for high-speed ball bearing. This method was used to obtain the optimum lubrication conditions of high-speed ball bearing. The optimum operating conditions that produce the optimum flow pattern were provided. The optimum annular flow was obtained by PAO6 oil with the low viscosity. Reynolds number influences the fluid shape and distribution of oil and air in pipe. The annular flow can be formed when Reynolds number is an appropriate value. The velocity distribution of oil-air two-phase flow at outlet was also discussed by different oil viscosities. The simulating results show that due to the effect of the oil viscosity and flow pattern the velocity decreased and expanded gradually close to the pipe wall, and the velocity increased close to the central pipe. The simulation results provide the proposal for the design and operation of oil-air two-phase flow lubrication experiments in the present work. This work provides a useful method in designing oil-air lubrication with the optimum flow pattern and the optimum operating conditions.

Tribological properties of low-temperature time-dependent pretreated graphite for mechanical seal pairs in high-speed turbopump

The friction coefficient and wear rate of pretreated graphite with liquid nitrogen were obtained by using a ball-on-disk tester,and the wear of GCr15–graphite seal pairs with the low-temperature time-dependent pretreatment was discussed by comparing the wear morphology.The results show that liquid nitrogen pretreatment can affect the hardness and interlayer spacing of graphite.The range of the friction coefficients of pretreated graphite changes from 0.17 to 0.22.With the increase of liquid nitrogen pretreatment time,the wear mechanism of graphite would change from dominated three-body wear to adhesion wear.The experimental results of the mechanical seal with liquid nitrogen pretreatment show that the wear rate of stator is less than 0.00165 mm^(3)·N^(−1)·m^(−1),and the graphite shows a good low-temperature compatibility.

Loading rate and holding load dependent room temperature nanoindentation creep behavior of 60NiTi alloy:Individual and coupling effects

60NiTi alloy is highly promising for aerospace bearings and mechanisms.Shock load that is inevitably generated during launching process brings about an quick loading process and transient load duration,and may further results in an unnoticed but detrimental creep deformation.On this account,the nanoindentation creep behavior of solution-treated 60NiTi alloy at room temperature and the corresponding influencing mechanism were studied.The results show that creep displacement was dominated by strain rate at the very beginning of holding stage.Strain rate and flow stress at the very beginning of holding stage were increased with an increased loading rate but declined with increasing holding load or with simultaneously increasing loading rate and holding load.The underlying mechanisms were provided as nucleation and absorption of geometrically necessary dislocations(GNDs)associated with strain gradient plasticity theory rather than the model based on the consumption of creep deformation at loading stage.

Enhanced micro/nano-tribological performance in partially crystallized 60NiTi film

The microstructure,mechanical and micro/nano-tribological properties of the 60NiTi film annealed at different temperature were investigated.The results reveal that annealing as-deposited 60NiTi film at 300,375,and 600℃ for 1 h leads to structural relaxation,partial crystallization and full crystallization,respectively.Compared with the structurally relaxed structure,the partially crystallized structure exhibits increased hardness but decreased elastic modulus.This is because that the elastic modulus is reduced by Voigt model while the hardness is improved by composite effect.Due to the highest hardness and ratio of hardness to elastic modulus(H/E),the partially crystallized 60NiTi film has the lowest penetration depth and residual depth(i.e.,groove depth).Besides,the results also reveal that ductile plowing is the dominant wear mechanism for all the annealed 60NiTi films.Under the condition of the ductile plowing,coefficient of friction and wear resistance are related to penetration depth and residual depth,respectively.Therefore,the partially crystallized 60NiTi film shows the best tribological performance at the micro/nano-scale.The current work not only highlights the important roles of hardness and H/E in improving the micro/nano-tribological properties but also concludes an efficient and simple method for simultaneously increasing hardness and H/E.