Current Issue : January - March Volume : 2020 Issue Number : 1 Articles : 5 Articles
A double reinforced layer on an aluminum alloy surface was produced using friction stir\nprocessing (FSP) by adding 34CrNiMo6 powder into Al (AA2024) substrate for better wear resistance\nand gradient transitions. The microstructures of the composites were analyzed using scanning\nelectron microscopy (SEM) and energy dispersive spectroscopy (EDS). The phase composition was\nexamined by X-ray diffraction (XRD). The results show that the double reinforced layer of the Al13Fe4\nintermetallic compound could be successfully fabricated via FSP. The volume fraction of Al13Fe4 in\nthe double reinforced layer was higher than in the single reinforced layer due to adding 34CrNiMo6\npowder and reinforced twice, and the Al13Fe4 particles were dispersed more homogeneously in the\ndouble reinforced layer. The interfaces between the double and single reinforced layer had a good\nmetallurgical bond. The microhardness of the double reinforcement layer was significantly increased.\nCompared with the AA2024 substrate, the microhardness of the double and single reinforced layers\nincreased five- (576 HV) and two-fold (254 HV), respectively....
The phenomenon that the hard abrasive grains repeatedly cut the surface\nmaterial of the parts during wear is very common in wear. In order to study\nthe influencing factors of mechanical damage, based on the three-body abrasive\nwear, this paper discusses the wear of the secondary cutting abrasive.\nFirstly, the secondary wear model of the hemispherical abrasive grain on the\nfriction pair surface is established. Secondly, the simulation experiment is\ncarried out on the secondary scratching of the abrasive wear on the surface of\nthe part. Next, the equivalent strain data and the equivalent stress data obtained\nby the experiment are subjected to secondary friction analysis. The final\nresults show that the secondary friction damage of the hemispherical abrasive\ngrain is greater than one wear....
To accurately study the dynamic characteristics of the spiral bevel gear transmission system in a helicopter tail transmission\nsystem, the finite element model of the gear shaft was established by a Timoshenko beam element, and the mechanical model of the\nspiral bevel gear was created by the lumped mass method. The substructure method is employed to extract the dynamic parameters\nfrom the gearboxâ??s finite element model, and the dynamic model of the spiral bevel gear-shaft-bearing-gearbox coupling\nsystem was built according to the interface coordination conditions. In the model, the influences of time-varying stiffness, a timevarying\ntransmission error, gearbox flexibility, unbalance excitation, and a flexible shaft and bearing support on the system\nvibration were taken into account simultaneously. On this basis, the dynamic differential equations of the full coupling system of\nthe spiral bevel gear were derived, and the effects of the gearbox flexibility, the shaft angle, and the unbalance on the dynamic\nproperties of the system were analysed. The results show that the gearbox flexibility can reduce the gear meshing force and bearing\nforce, in which there is a more significant impact on the bearing force. The shaft angle affects the position, size, and direction of the\nsystemâ??s axis trajectory. Meanwhile, the meshing force and the bearing force of the system are also varied because of the various\npitch angles of the driving and driven gears under different shaft angles. The unbalance of the gear shaft has an effect on the\nvibration of the spiral bevel gear transmission system in all directions, wherein the influence on the torsional vibration is the most\nsignificant, and the influence increases as the unbalance rises. The unbalance of the gear shaft also affects the meshing force and\nbearing force, which increases as the rotational speed rises. This research provides a theoretical basis to optimize dynamic\nperformance and reduce the vibration and noise of a spiral bevel gear full coupling system....
We report the results of the influence of acetylene and oxygen gas pressure on the\ncorrosion resistance of bronze-aluminum coatings deposited on a naval brass substrate by means\nof the thermal (flame) deposition process. The coatings were characterized by means of scanning\nelectronic microscopy (SEM), energy-dispersive X-ray spectrometry (EDS), X-ray diffraction (XRD),\nX-ray fluorescence (XRF), and transmission electron microscopy (TEM). The corrosion tests were\ncarried out via Tafel and electrochemical impedance spectroscopy (EIS). In addition, some samples\nwere selected in order to investigate heat treatment and its effects on corrosion resistance. The results\nindicate that changes in the pressure and flow of the gas affects the composition, morphology,\nand physical properties of the coatings, and these effects have consequences for the behavior of the\ncoatings when they are immersed in corrosion environments. The collision speed of the particles\nwas identified as the most significant factor that influences the properties and the performance\nof the coating. The gas pressure modified the oxides and the porosity level, which improved the\ncorrosion resistance....
The frictional resistance and machining quality when cutting carbon fiber\nreinforced plastics (CFRP) laminates are associated with tribological behavior\nof tool materials. In the present study, the tribological properties of three\ntypes of monolayer microcrystalline diamond (MCD) coatings, nanocrystalline\ndiamond (NCD) coatings and dual-layer MCD/NCD coatings sliding\nagainst CFRP are investigated under dry lubricated conditions using the rotational\nfriction tester. The coefficients of friction (COF), wear rate and worn\nsurfaces of the contacted surfaces are analyzed for the MCD-CFRP,\nNCD-CFRP and MCD/NCD-CFRP contacting pairs. The results show that\ncompared with the monolayer MCD and NCD, the bilayer of MCD/NCD\ncoating displays the lowest COF with the value of ~0.13, it is 42% and 55% of\nthe values for MCD and NCD coatings. Due to the rough surfaces of MCD,\nthe wear debris of CFRP on MCD samples exhibits the plowing effect. While\nfor the NCD and MCD/NCD samples, the wear fragments display the planar\nshapes. The wear rate of CFRP against MCD is more than twice that of CFRP\nagainst NCD, due to the excellent loading capacity. While the wear rate of\nCFRP against MCD/NCD is about twice than that of CFRP-NCD pairs. The\nbilayer of MCD/NCD combines the excellent advantages of high hardness of\nMCD and the smooth surface of NCD. It shows the broad application potential\nfor the bilayer coatings....
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