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Abstract In this paper, a new friction-induced nanofabrication method is presented to fabricate protrusive nanostructures on quartz surfaces through scratching a diamond tip under given normal loads. The nanostructures, such as nanodots, nanolines, surface mesas and nanowords, can be produced on the target surface by programming the tip traces according to the demanded patterns. The height of these nanostructures increases with the increase of the number of scratching cycles or the normal load. Transmission electron microscope observations indicated that the lattice distortion and dislocations induced by the mechanical interaction may have played a dominating role in the formation of the protrusive nanostructures on quartz surfaces. Further analysis reveals that during scratching, a contact pressure ranged from 0.4Py to Py (Py is the critical yield pressure of quartz) is apt to produce protuberant nanostructures on quartz under the given experimental conditions. Finally, it is of great interest to find that the protrusive nanostructures can be selectively dissolved in 20% KOH solution. Since the nanowords can be easily 'written' by friction-induced fabrication and 'erased' through selective etching on a quartz surface, this friction-induced method opens up new opportunities for future nanofabrication.

Corrugated damage to bearings is a common fault in electrical facilities such as new energy vehicles, wind power, and high-speed railways. The aim of this article is to reveal the microscopic characteristics and formation mechanism of such damages. The corrugation with alternating "light" and "dark" shape was produced on GCr15 bearing races in the experimental conditions. Compared to the light area, the dark area (in the images generated by optical microscope) has more severe electrical erosion, lower hardness, more concave morphology, and lower oxidation. As the voltage increases, the width of the corrugation, the height difference between corrugation, and surface roughness all increase. It is believed that the formation of corrugated damage requires a sufficiently high voltage to induce the periodic destruction and reconstruction of the lubrication film. When the bearing is in a metal-lubrication film–metal contact state, the high voltage causes the lubrication film to break down and induce electrical erosion. Then, the contact area is in metal–metal contact, and the surface is mainly damaged by mechanical rolling. After the reconstruction of lubrication film, the next round of electrical erosion begins. The results are helpful for a deeper understanding of the mechanism of bearing erosion in electrical application. [ABSTRACT FROM AUTHOR]

Due to the high speed and high pressure operating conditions, wear between the finger seal and the rotor is inevitable, and this leads to an increase of leakage clearance and becomes an important factor affecting the seal life. The theory of anisotropic elasticity was employed to describe the mechanical characteristics of the seal material. An improved Archard wear model was proposed to calculate the nodal wear rate, and the local wear direction was also determined. The wear simulation model and procedure were established based on the Arbitrary Lagrangian Eulerian adaptive mesh strategy. The effects of material density, fabric orientation, pressure differential and rotor speed on the wear characteristics of finger seal and the change of leakage clearance caused by wear loss were studied. The results show that the wear first occurs at the heel area of the finger foot bottom and gradually extends to the toe area. C/C (carbon fibre reinforced carbon matrix) composite finger seal with higher material density has smaller leakage clearance and wear depth. With the increase of fabric orientation angle, the wear depth in the heel area of finger foot is smaller, and the circumferential wear area is narrower. The average wear depth of finger seal decreases with the orientation angle. When the orientation angle is 0, the seal leakage clearance is smaller. The increase of pressure differential not only aggravates the seal wear, but also expands the wear area, and also increases the average contact pressure and leakage clearance. Increasing the rotor speed make the wear depth of the heel area of finger foot gradually increase, but the wear area becomes narrower. The average contact pressure decreases and the average leakage clearance increases. This study provides a theoretical method and basis for the prediction and evaluation of the wear life and performance of C/C composite finger seal. [ABSTRACT FROM AUTHOR]

Ultrafine-grained or nanocrystalline Mo-12Si-8.5B alloys possess more excellent strength than those of the coarse-grained ones, but they often exhibit limited fracture toughness at room temperature. It's very important to simultaneously enhance the strength and toughness of Mo-12Si-8.5B alloy for their practical applications. In the present study, nanometer Mo-ZrO2(Y2O3) composite powder was successfully prepared by a combination of sol-gel and one-step high-temperature reduction in hydrogen. A series of Mo-12Si-8.5B-ZrO2 (Y2O3) alloys composed of different proportions of coarse and fine Mo grains were fabricated via spark plasma sintering using nano- and micro-Mo powders as raw materials. With an increase of the mass ratio of the nanometer Mo to the micrometer Mo in the alloy, the hardness, flexural strength and fracture toughness first increase and then drop. As the mass ratio of the nanometer Mo powder to the micrometer Mo powder is 3:7, the bimodal structural alloy possesses the excellent comprehensive mechanical properties, including the hardness of 9.75 GPa, the flexural strength of 630 MPa, and the fracture toughness of 12.82 MPa m1/2. Grain refinement of the Mo, grain boundary strengthening in the boundary between the nanometer/micrometer Mo grains and the second-phase strengthening of the nano-ZrO2(Y2O3) particles attribute to the enhancement of the hardness and flexural strength. The improved fracture toughness mainly results from the crack arrest effect of the coarse grain Mo. [ABSTRACT FROM AUTHOR]

CF/PEEK composites were prepared by vacuum hot pressing sintering technology. The thermal properties of the materials were tested by thermal conductivity analyzer and TG tester. Multifunctional friction and wear testing machine, 3D morphology profilometer, scanning electron microscope and friction electrometer were used to analyze the friction and wear properties and anti-friction electrostatic properties of the materials. The results show that with the increase of the forming temperature, the friction coefficient and wear rate of the materials decrease gradually. With the increase of CF contents, the friction coefficient, wear rate and friction electrostatic voltage decrease first and then increase. When the CF content is as 20%, the friction coefficient, wear rate and friction electrostatic voltage reach the lowest values, which are as 0.247, 5.6 x 106 mm/(N ⋅ m) and 3.3 V, respectively. Friction and electrostatic data show that the CF/PEEK materials prepared by this method have better friction properties and anti-electrostatic properties than that of commercial composites. The wear mechanism of CF/PEEK composites is mainly adhesive wear, accompanied by slight abrasive wear. [ABSTRACT FROM AUTHOR]

A novel rotating conductive joint consisting of an inner raceway, an outer raceway, and an elastic ring was proposed in this study. The elastic ring was clamped between the inner and outer raceways using elastic compression force. The effect of the elastic force on the current-carrying properties and the damage of the ring material was investigated. As the elastic force increased from 10.2 N to 20.4 N, the total frictional force decreased from 15.5 N to 9.5 N, and the contact resistance decreased from 0.37 Ω to 0.18 Ω. While monitoring the revolution and rotation of the elastic ring, it was observed that the slip-rolling ratio decreased from 43.04% to 31.74%. Furthermore, a low friction coefficient was obtained under a high elastic force, which could be attributed to the small slip-roll ratio. The scanning electron microscopy and optical microscopy results revealed that a low friction coefficient led to subsurface crack initiation and a low degree of grain deformation. When the friction coefficient at a single contact point was greater than 0.34, fatigue occurred directly on the contact surface. The high friction-induced plastic deformation could cause surface hardening. Therefore, a high friction coefficient and large surface fatigue did not lead to high wear at low elastic forces. [ABSTRACT FROM AUTHOR]

Electrical erosion pit is a fundamental manifestation of electrical bearing damage. As the shaft voltage increased, the degree of electrical damage became more severe, and the residual compressive stress and hardness of bearing surface decreased. The transition of martensite into ferrite induced by high discharge temperature was found at the edge of the erosion pit using a transmission electron microscopy. This phenomenon has not been observed below the mechanically rolled surface under the same conditions. Electrical penetration harmed the bearing through surface erosion, lubrication deterioration and martensite decomposition. The electrical pit could be observed when current density exceeded 0.95 A/mm2. The results can help understand bearing failure in the fields of railways, wind turbines, and new-energy vehicles. • Transformation of martensite into ferrite have been observed around erosion pit. • Segregation of carbides at subsurface was the results of martensitic decomposition. • Residual stress and hardness decreased in the erosion surface. [ABSTRACT FROM AUTHOR]