查看更多>>摘要：The addition of NbC to high chromium white cast irons (WCIs) has potential to improve component wear lives in mining and ore beneficiation environments, due to the combined presence of Cr-rich and niobium carbides. While the effect of chromium carbide volume fraction (Cr-CVF) on abrasion performance of plain-Cr WCIs is well understood, its effect on NbC-bearing WCIs is unknown. This work studies the effect of Cr-CVF on high-stress abrasion of this newer class of dual-reinforced high-Cr WCIs, using the ball mill abrasion test with quartzite and basalt. The alloys cover a wide range of Cr-CVF, from M_7C_3-free NbC-reinforced steel to hyper-eutectic WCI. Bulk hardness increased linearly with Cr-CVF, at a rate of 3.9 HV per 1% Cr-CVF. In basalt, abrasion resistance increased linearly with Cr-CVF, at an average life improvement rate of 24% per 1% Cr-CVF. This confirms that performance is maximized by increasing Cr-CVF even in the presence of substantial volumes of cubic carbides. In quartzite the trend is again linear up to 30 vol% M7C3 (3.7% life increase per 1% Cr-CVF), but the hyper-eutectic alloy shows poorer resistance than slightly hypo-eutectic alloy. SEM studies of the worn surfaces demonstrate that micro-fracture of the hard carbides was the controlling damage mechanism. Primary M7C3 was observed to suffer fragmentation in high-stress abrasion in quartzite, confirming the expectation from the quantitative trend.
查看更多>>摘要：Microstructural-related deformation behaviour at grain levels significantly affects mechanical properties of crystalline materials. Particularly, crystallographic orientations and grain boundaries play crucial roles in the friction and wear performance of polycrystalline materials at the microscale. In this study, experiments and corresponding crystal plasticity finite element simulations are conducted using a spherical indenter to illustrate the underlying effect of crystallographic orientations and grain boundaries on the nanoscratching behaviour of a unique bi-crystal Cu. The indenter size and process parameters in simulations are consistent with experiments, and crystallographic orientations of two designated individual grains on the polycrystalline surface are determined via electron backscatter diffraction pattern. The simulation results show that crystallographic orientations significantly affect the plastic deformation of the target material by activating different slip systems. Grain boundary can act as an obstacle as well as a starting point of the dislocation movement, leading to anisotropic wear behaviour in the vicinity of the grain boundary. Furthermore, the simulated scratched surface morphology of the bi-crystal Cu quantitatively shows good agreement with the experimental results.
查看更多>>摘要：Disc cutter is mainly used in cutting through hard rock. Disc cutter wear is inevitable during tunnel boring machine (TBM) tunneling, and excessive wear can lead to a decrease in tunneling efficiency and increase construction risks. Therefore, the importance of predicting the disc cutter wear accurately and arranging the cutter change plan can never be overemphasized. In this study, disc cutter wear data and replacement records for three shield chamber openings were analyzed, which were collected from a water conveyance tunnel project in Guangdong, China. It was found that the normal wear failure accounted for approximately 76.19%, while the abnormal wear failure accounted for 23.81%, and the range of tools to be replaced due to normal wear continues expanded as the tunneling distance increased. Based on the observed wear data, it is found that the wear rate of edge tools is much lower than that of center tools, which does not conform to the normal wear rules. Subsequently, a new disc cutter wear prediction model was developed considering energy conversion and uneven thrust distribution for explaining this problem. The determination method of the energy conversion coefficient k and thrust distribution coefficient b was proposed, and they had been obtained from the wear data in the first replacement. On the other hand, the proposed model has higher accuracy in both cutter wear and cutter change range prediction compared with the existing models. However, the prediction accuracy of the proposed model will decrease with the increase of the tunneling distance, so the undetermined coefficients k and b need to be updated in a timely manner.
查看更多>>摘要：Electro-Fenton polishing is a chemical mechanical polishing (CMP) technology with enhanced chemical reaction, which hydroxyl radicals (·OH) can be efficiently and controllably generated by using an electric Fenton method. The oxidation and corrosion of single crystal gallium nitride (GaN), and the synergistic mechanism of chemical and mechanical effects in the electro-Fenton polishing process are key to the electro-Fenton polishing of GaN. This article evaluated the effects of different media (electrolyte, H_2O_2, Fenton, and electro-Fenton) and different conditions (H_2O_2 mass fraction, means of H_2O_2 addition, cathode potential, Fe-C catalyst mass fraction, and pH) through ball-disk friction and wear tests. The results showed that electro-Fenton media demonstrated the best oxidation and corrosion effects on the GaN surface among the four media. In the electro-Fenton slurries, the oxidation was very sensitive to the H_2O_2 mass fraction which showed that 5 wt % H_2O_2 was the optimal mass fraction; the oxidation efficiency was greatly improved by regularly supplementing H_2O_2. The friction and wear behavior of GaN exhibited a good response to the cathode potential with the optimal cathode potential being - 0.5 V. Meanwhile, the best Fe-C catalyst mass fraction was 3 wt % and the optimal pH was 2. In addition, the friction and wear behavior were investigated, and the energy spectrum tests was carried out to verify the effect of the chemical reaction. The synergistic mechanism of chemical action and mechanical removal in the friction and wear process was revealed. This research provides theoretical support for on-line electro-Fenton polishing technology.
查看更多>>摘要：Graphene-based nano lubricant additives attract more and more attention because of their superior lubricating performance as well as green and ashless properties. Graphene-based nanocomposites exhibit excellent tribological performances due to the synergistic "slide-roll" effect. In this work, we developed a novel nanocomposite constructed by graphene materials (G) and CuO nanoparticles, named CuO@G, which has superior tribological properties to each component (pure CuO or pure graphene materials) and the mixture (Graphene + CuO) under different testing conditions due to the synergistic effect. By adding 0.5 wt% CuO@G to PAO-6 oil, the coefficient of friction (COF) is reduced by more than 50%, and the wear scar almost disappears. The study provides a novel and promising method for the synthesis of graphene-based lubrication nanomaterials, which has high potential for lubrication applications.
查看更多>>摘要：Aluminum alloys are used in various industries due to their favorable mechanical properties. In terms of machinability, adding silicon to the chemical composition can provide the association of wear mechanisms. Improvements in wear resistance have been addressed in processes for applying coatings to cutting tools, allowing for work at higher cutting speeds. This study applied microstructural characterization techniques, mechanical and tribological properties that could be correlated with possible performance gains when DLC was applied to carbide tools. Tribological tests indicated resistance to abrasive wear and reduced coefficient of friction when using DLC. During machining tests with aluminum alloy, the presence of DLC provided less significant changes in the quality of holes at different cutting speed.
Amod KashyapA. P. HarshaP. KondaiahHarish C. Barshilia...
14页
查看更多>>摘要：Galling has been a severe concern in oil - gas, automotive, and nuclear sectors. SS 304 steel is used in these industries despite its low galling resistance because it possesses good corrosion resistance properties. The threads of bolt, nut or a tapped hole and fasteners made of SS 304 experience severe damage due to galling or cold working. Therefore, the galling characteristics of the coated SS 304 samples were studied against the uncoated counterpart. A multilayer coating of molybdenum (Mo) and diamond like carbon (DLC) was deposited through dual sputtering using a high power impulse magnetron sputtering (HiPIMS) power source for graphite target and pulsed DC power source for Mo target. The Mo/DLC multilayer coating was optimized for antiwear and low friction properties. The evaluation of friction properties was done through a nanotribometer. The galling samples of SS 304 steel were prepared following the ASTM G196 standard, and the optimized coating was deposited on the galling samples. The adhesion strength of the coating was analyzed with the help of a nanoscratch tester. The galling behavior of coated and uncoated samples was investigated at room temperature (RT) and 300℃. Galling damage was quantified by calculating the galling area on the galled sample. Image processing and computer vision tools were used to calculate the galled area. The tribopair having coated (Mo/DLC multilayer coating on SS 304) and the uncoated sample (SS 304) showed lower galled area than the tribopair containing both uncoated samples in every test conditions. At RT the coated sample failed at 15 MPa, whereas the uncoated samples failed at 5 MPa. Similar type of results were obtained when the samples were tested at 300℃. The characterization of the coating and the mechanism of galling were studied in detail with the help of Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nanoindentation, stereo-zoom optical microscopy, and scanning electron microscopy (SEM).
查看更多>>摘要：Water-lubricated ceramic sliding tribosystems, when operating under superlubricity conditions, reduce frictional energy losses in many applications. Aqueous superlubricity of 5 dissimilar ceramic tribopairs (Si_3N_4-Al_2O_3, Si_3N_4-ZTA, Si_3N_4-SiC, Al_2O_3-SiC, ZrO_2-SiC) was thus studied in a series of ball-on-disk tests, with the identification of wear mechanisms and lubrication regimes, while introducing a running-in wear map approach to elucidate transient tribological phenomena. All pairs presented superlubricity for certain combinations of normal load and sliding speed, after a running-in period where mechanical and thermal severities of contact remained mostly below their respective threshold values, promoting mild wear regimes. Load-carrying capacity of ZrO_2-SiC was the highest due to high homogeneity and low roughness of the tribofilm on SiC disk's wear track.
查看更多>>摘要：FZG tests have become a standard for the determination of fatigue lifetime and other key operational parameters in gear applications. This testing configuration is considered to be closer to the real-field application than other rigs such as twin disc testers, although FZG requires a significantly more complex sample preparation in addition to not allowing for the variation of key test parameters. Despite the fact that DIN 3990 recommends the use of disc tests if no other gear test results are available, it must be noted that the transferability of results from twin disc to FZG gear tests has not been properly assessed in the available literature. For the present study, gears made of case hardened 22MnCr5 with different carburisation depths were tested under lubricated conditions using a FZG test rig. The results, including S-N curves, were compared with twin-disc tests performed by the authors with modified disc geometries, in order to assess the transferability of the results between both configurations. Additionally, worn samples have been characterised in terms of residual stresses and microstructure for one case hardening depths in FZG tests at different tooth flank locations and compared with disc tests. It has been found that a good match between FZG and twin disc test rig results can be found for an appropriate twin disc sample geometry and hardness distribution, opening the way for transferability between both test configurations.
S. A. RodriguezJ. J. CoronadoC. C. Saenz-Betancourt
11页
查看更多>>摘要：Erosive wear due to cavitation severely affects hydromachinery and consequently various sectors of industry, including hydroelectric plants. ASTM A743 CA6NM steel, which is typically used in hydromachinery, was boronised using the packing method at 950℃ for durations of 2, 6, and 8 h Fe2B and FeB phases were identified and characterised using optical microscopy, X-ray diffraction, scanning electron microscopy, and microhardness tests. Under all of the boronising conditions, a surface FeB phase was obtained. Its hardness was 5.22 times that of the base material. The resistance to erosion due to cavitation was evaluated according to the ASTM G32 standard by exposure for 15 h to vibrations that induced cavitation. The boronising time influenced the resistance to cavitation. After boronising for 2, 6, and 8 h, the erosion rates were reduced by 72%, 57%, and 55%, respectively, compared to the erosion rate of untreated ASTM A743 CA6NM steel. According to scanning electron microscopy, the worn surfaces differed for non-boronised steel (ductile behaviour) and boronised steels (brittle behaviour) exhibiting micro-cracks, micro-pores, and detachment of the boride layers.
NSTL
Elsevier