Max SchneckenburgerRui AlmeidaSven HoflerRainer Borret...
7页
查看更多>>摘要：Robot polishing is increasingly being used in the production of high-end glass work pieces such as astronomy mirrors, lithography mirrors, laser gyroscopes or high-precision coordinate measuring machines. The quality of optical components such as lenses or mirrors can be described by shape errors and surface roughness. Whilst the trend towards sub nanometre level surfaces finishes and features progresses, matching both form and finish coherently in complex parts remains a major challenge. With increasing optic sizes, the stability of the polishing process becomes more and more important. Polishing agent nozzles supply the polishing process with sufficient polishing agent and it is assumed that this slurry erosion has an influence on the material removal. To investigate this, a static test set-up was built. The primary aim of this paper is to point out and raise awareness of the problem of slurry erosion in glass polishing and the influence of slurry erosion by conventional polishing nozzles is shown. From an angle of 30°, the nozzle turns into a fluid jet tool and removes material independently.
查看更多>>摘要：The microstructure of the 'flow lip' formed at the lower gauge face in high rails in curved tracks has been investigated along the transverse section. The rails served in tracks having radii of curvature of 1500 m(S1) and 2000 m(S2) respectively. Optical images reveal the formation of an outermost white etching layer (WEL) followed by a brown etching layer (BEL) and deformed sublayers. Cracks originated from the WEL regions and from the notches at the extreme end of the flow lip. The cracks originate from the WEL region due to exhaustion of ductility, whereas, at the extreme end of the flow lip the cracks originate due to stress concentration caused by the notches generated due to uneven plastic flow of material. Using SEM (scanning electron microscopy) and EBSD (electron back-scattered diffraction), the WEL region is identified to consist of fine grains of ferrite and particles/fine fragments of cementite. The cementite in the WEL region is present as particles in S1 and as broken fragments as well as particles in S2. From the SEM images, the BEL has a similar appearance to WEL but with intermittent patches of lamellae-type features. The lamellae type features are much larger in S2 than S1 implying that the radius of curvature can significantly affect the level of deformation. The deformation was lower in S2 than S1 for similar distances from the outer edge, possibly due to less severe shear loading in a less sharply curved rail.
查看更多>>摘要：Hybrid reinforced aluminum-based composites with a silicate component with pozzolanic activity and silicon carbide ceramic particles as reinforcement phases can form an iron-poor friction transfer film during the friction process, thereby making the aluminum-based composites exhibit a high friction coefficient and a low wear rate characteristics. The phase composition in the friction transfer film was investigated utilizing focused ion beams, transmission electron microscopy, and energy-dispersive X-ray analysis. The results showed that the friction transfer film was mainly composed of nanosized aluminum, ultra-fine aluminum, and crushed silicate particles, which interwove into a nano-network structure to protect the matrix and improve the friction performance.
查看更多>>摘要：Germanium (Ge), as a higher mobility material, presents great merits for future semiconductor field-effect transistor devices. Extremely smooth Ge surface is required for high-performance devices, which depends on mechanical surface planarization. However, the defects generated during surface manufacturing usually degrade device performance, which are desired to be minimized to improve the performance and service life of Ge-based products. In this paper, when a light normal load was applied on monocrystalline Ge surface by an atomic force microscope (AFM), the pile-up was generated in the scratched area under line-scan mode by a diamond tip. The formation of the pile-up intensely depends on the contact pressure, and the threshold is about 10.7 GPa, which is close to the microhardness of Ge. Unlike the formation of anodized hillock, the amorphization of Ge was found to be the main contributor to the pile-up induced by the scratch, rather than the oxidation. Based on chemical composition and microstructure detections, it suggests that the pile-up is constructed by thin oxide layer (possibly GeO_x (x≤2)) on the surface, thick amorphous layer in the middle and deformed Ge (lattice dislocations excluding amorphization) at the bottom. These findings provide a fundamental understanding of the light-load machining process on monocrystalline Ge surface.
查看更多>>摘要：The internal lubrication of polyimide (PI) with added 5-wt% nanographite (NG) was investigated in comparison to the tribological performance of a neat PI under point-contact dry sliding conditions with various loads and velocities. NG had a vital role in eliminating the influence of macromolecules decomposed in the PI matrix, according to energy-dispersive X-ray spectrometry, Fourier-transform infrared spectroscopy, and Raman spectroscopy results. When the pressure × velocity reached 56 MPa m/s, a sharp increase was observed in the wear rate of the neat PI. The wear debris consisted of coexisting PI matrix and amorphous carbon. In contrast, NG filler and PI matrix mixtures were the main components in the NG/PI debris. The effect of the NG with a high thermal conductivity on the frictional interface likely prevented the pyrolysis of the PI matrices. Compared to the neat PI, the variations in tribological properties of NG/PI were less affected by the test conditions. For NG/PI, the wear gradually converted from adhesive wear under light load/low velocity to abrasive wear under heavy load/high velocity. The results for the tribological performance and wear mechanism of NG/PI could further contribute to applications under various point-contact dry sliding conditions.
Ana Paula Gomes NogueiraGustavo da Silva GehlenPatric Daniel NeisNey Francisco Ferreira...
10页
查看更多>>摘要：The addition of the rice husk in a new eco-friendly Cu-free brake pad formulation was investigated in this study. Rice husk (RH) is a natural agro-waste residue with relatively high silica content, which should display abrasive properties that are not easily found in other natural materials. In this study, tribological properties of three friction materials were investigated using a pin-on-disc (PoD) tribometer. The three formulations were prepared adding to a common composition, each one of the following components: 6 wt% of grinded rice husk (material code: F-RH); this same amount of rice husk, after heat treatment at 600℃ (material code: F-RHT); and finally 6 wt% of alumina (F-AL) in place of rice husk, respectively. This latter material was meant to characterize the specific role of the natural ingredient. During PoD tests the evolution of the friction coefficient was followed, along with the concentration of the emitted airborne particles. The F-RHT showed very promising properties, depending on the particular characteristics of the friction layer forming onto the pin surface. This layer turned out to be compact and it was highly covering the surface of the F-RHT material, thanks to the positive effect of the silica particles from RH. The F-RH featured good behavior in terms of low wear and low emissions. In both cases, the rice husk showed up as a potential valuable alternative as a natural brake pad ingredient.
查看更多>>摘要：The operating conditions of hoisting wire ropes are extremely harsh in coal mines, which often accelerates wear due to lubrication failure. This paper starts with the modification of lubricating oil to improve the service life of wire ropes in mine hoists under severe working conditions. First, the modification methods of octadecylamine functionalized graphene oxide (ODA-GO) and its reduced product by hydrazine hydrate (ODA-rGO) were introduced, followed by characterization with Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), X-Ray diffraction (XRD), Raman spectroscopy, thermogravimetric (TG) spectroscopy and transmission electron microscope (TEM). Then, the dispersion stabilities of these additives in IRIS-550A lube oil (IRIS) were recorded and quantitatively analysed by a UV-Vis spectrophotometer. Finally, the tribological properties of ODA-GO-and ODA-rGO-modified oils were evaluated through a four-ball tribotester, and ODA-GO-modified oil was further tested using a wire rope sliding wear rig under different contact loads and sliding speeds. The results show that octadecylamine is attached to graphene oxide (GO) through covalent bonds. ODA-GO shows a better dispersion stability in IRIS than ODA-rGO due to its high concentration of octadecyl chains. The coefficient of friction (CoF) between wire ropes varies under different test conditions, but the wear is reduced in all cases.
A. YounesH. Izadi-GonabadiR. Martinez SanchezS. J. Bull...
11页
查看更多>>摘要：The combined effect of the cooling rate and microalloying has been studied from suction casted Cu_(50)Zr_(50), Cu_(49.5)Zr_(50)Fe_(0.5) and Cu_(49)Zr_(50)Fe_1 at.% rods of 2 mm and 4 mm diameter. For the 2 mm samples, ～1000 K/s cooling rate, the microstructure mostly consists of B2 CuZr austenite and it is basically the same for all compositions. However, 0.5 at.% Fe addition promotes the formation of stress-induced B19' martensite upon wear testing thus improving the wear resistance of the alloy. For the 4 mm samples, ～250 K/s cooling rate, a multiphase intermetallic is predominant and when microalloyed with 0.5 at.% Fe, a relatively large volume fraction of as-cast B33 CuZr martensite is formed thus resulting in a reduction of the wear resistance. At high cooling rate the wear mechanism is predominantly delamination wear while for low cooling rate the large continuous grooves are indicative of abrasive wear.
Daniel GrasserSantiago Corujeira GalloMichael PereiraMatthew Barnett...
14页
查看更多>>摘要：Reducing abrasive wear is crucial to minimising economic losses in bulk solids handling, particularly in the mining industry. The present study investigates the wear behaviour of macro-scale composites, consisting of hard inserts equi-spaced in a soft matrix, with a length-scale comparable to the size of abrasive particles. The experiments explored the effect of insert spacing on the formation of protective particle layers to reduce wear. Hardened tool steel inserts were embedded in a soft aluminium matrix. The spacing between inserts decreased with increasing volume fraction of inserts (8, 23 and 40 vol%). An instrumented dry sand rubber wheel test was used to conduct accelerated wear tests, and to measure the thickness of the protective abrasive particle layer formed during the tests. The soft aluminium matrix wore preferentially, leaving the tool steel inserts standing proud. The exposure height of the inserts reached a steady state for extended wear stages. Interestingly, the composites with 23 and 40 vol% of inserts showed significantly less wear than predicted by the rule of mixture. When the insert spacing was equal to the abrasive particle size, the thickness of the abrasive particle layer was larger than for specimens without inserts. This study reveals that the spacing between the inserts, with respect to the abrasive particle size, is an important design parameter for the development of enhanced wear resistant composites.
查看更多>>摘要：The tribological performance and rolling lubrication properties of the BP/TiO_2 nanocomposites as water-based lubrication additives (BP/TiO_2-WL) were investigated by the ball-on-disc tribometer and four-high rolling mill. The results indicated that the average coefficient of frictions (COFs) and wear rate of the 0.08 wt% BP/TiO_2-WL were reduced by 24.5% and 59.5%, respectively, compared with ultrapure water. The lubrication mechanisms of the BP/TiO_2-WL were dominated by the synergistic effect between the BP nanosheets and TiO_2 nanoparticles and the formation of tribological reaction films. In addition, due to the addition of the BP/TiO_2 composite nanofluids, the rolling force and surface roughness of the titanium alloy plate during the rolling process were decreased by 17.5% and 32.2%, respectively. Therefore, BP/TiO_2 nanocomposites as water-based lubrication additive have shown potential application in the field of titanium alloy plate cold rolling.
NSTL
Elsevier