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Transmission gear is a key component of vehicles and its surface integrity affects the safety of the transmission system as well as the entire mechanical system. The design and optimization of allowances in form grinding are important for improving dimensional accuracy and machining efficiency during the manufacturing of heavy-duty gears. This work aims to investigate the effects of grinding allowance allocation on surface morphology, grinding temperature, microstructure, surface roughness, and microhardness fluctuation during the form grinding of 20Cr2Ni4A gears. Results indicated that grinding temperature was primarily influenced by rough grinding involving significant grinding depths exceeding 0.02 mm. The ground surface exhibited slight work hardening, while thermal softening led to a reduction in microhardness of around 40 HV. Ground surface roughness Ra varied from 0.930 μm to 1.636 μm, with an allowance allocation of the last two passes exerting the most significant influence. Analysis of surface and subsurface microstructures indicated that a removal thickness of 0.02 mm during fine grinding was insufficient to eliminate the roughness obtained from rough grinding. Evident ridges, gullies, and surface defects such as material extraction, adhesion, and plastic deformation were also observed. The proposed grinding strategy was validated in practical manufacturing with good surface quality and geometrical accuracy. [ABSTRACT FROM AUTHOR]

This work aims to research the influence of boron and quenching temperature on the microstructures and performances of boron-bearing high-speed alloy steel. The results showed that the hardness and wear resistance of boron-bearing high-speed alloy steel were improved after increasing the boron content. The volume fraction of boron-rich carbide gradually decreased, and the hardness increased significantly with the rise in quenching temperature. The highest comprehensive mechanical properties were obtained for samples quenched at 1040 °C. The TEM results showed the boron-rich carbide was M7(C, B)3 with an HCP structure, and the precipitated particles were M23(C, B)6 with an FCC structure after tempering. This work may help improve the wear resistance of materials in the field of surface coatings. [ABSTRACT FROM AUTHOR]

This work focused on removed mode of titanium target material and deposition process of the TiN film in a novel dual pulse power magnetron sputtering (DPPMS), which could improve deposition rate and properties of the TiN film. The study was carried out using DPPMS with different target power ratios between the first and the second ionized periods (P w /P s). It was found that when P w /P s was changed from 0.9/1.6 to 0.3/2.2, the removed mode of target material changed from sputtering to sputtering and evaporation, and the deposition rate of TiN films increased from 26 to 61 nm/min. All TiN films showed face center cubic (fcc) crystal structure and typical columnar microstructure. The compactness and size of columnar structure were improved with P w /P s changed from 0.9/1.6 to 0.3/2.2. Additionally, the hardness of TiN film deposited at P w /P s of 0.3/2.2 reached up to 25.4 GPa. [ABSTRACT FROM AUTHOR]

Recent years have witnessed a growing research interest in graphene-reinforced alumina matrix composites (Al2O3-G). In this paper, to better achieve the dispersion of graphene in composites, a ball milling method for adding raw materials step by step, called stepwise feeding ball milling, was proposed. The Al2O3-1.0 wt % graphene composites were prepared by this stepwise feeding ball milling and hot pressing. Then, the effects of sintering temperature and sintering pressure on the microstructure and mechanical properties of composites were studied. Results showed that the bending strength, fracture toughness and Vickers hardness of composites increased firstly and then decreased with increasing sintering temperature. The mechanical properties of composites were all at their maximum with the sintering temperature of 1550 °C. For example, the bending strength of composites reached 754.20 MPa, which was much bigger than 478.03 MPa at 1500 °C and 364.01 MPa at 1600 °C. Analysis suggested that the strength of composites was mainly related to the grain size, microflaw size and porosity. [ABSTRACT FROM AUTHOR]

Considering that it is difficult for traditional materials to simultaneously meet the requirements for filling grouting of water-filled karst caves and subsequent shield tunneling, an environmentally friendly and controllable new underwater cementitious filling material (NUC-FM) is developed, with abandoned shield mud as the basic raw material. Through laboratory tests, the mechanical property parameters of NUC-FM are tested, and its micromechanism is analyzed. The research results show that there is excellent synergistic interactions among shield mud, cement, flocculant, fly ash and other raw materials. The NUC-FM grouting filling material with superior performance can be prepared when the water binder ratio is between 0.45 and 0.6 and the water consumption is between 270 and 310 kg/m3. It has the characteristics of non-dispersion underwater and moderate consolidated body strength. The compressive strength of the NUC-FM consolidated body samples under each mix proportion is much higher than 0.5 MPa, which meets the technical strength requirements of a construction site, and the microstructure shows that there is an obvious dense and stable block structure inside. The cost of the NUC-FM prepared with an optimized mix proportion is only 34.57 dollars/m3, which is far lower than the market purchase price of concrete and cement mortar. It can be predicted that the NUC-FM is an ideal filling grouting material for water-filled karst caves in shield tunnels in water-rich karst areas. [ABSTRACT FROM AUTHOR]

In the current study, we evaluate the equivalent stiffness of peritubular reinforcement effect (PRE) of porous dentine optimized by the thickness of peritubular dentine (PTD). Few studies to date have evaluated or quantitated the effect of PRE on composite dentine. The miscrostructure of porous dentine is captured by scanning electron microscope images, and then finite element modeling is used to quantitate the deformation and stiffness of the porous dentine structure. By optimizing the radius of PTD and dentine tubule (DT), the proposed FE model is able to demonstrate the effect of peritubular reinforcement on porous dentine stiffness. It is concluded that the dentinal equivalent stiffness is reduced and degraded with the increase of the radius of DT (i.e., porosity) in the certain ratio value of Ep/Ei and certain radius of PTD, where Ep is the PTD modulus and Ei is the intertubular dentine modulus. So in order to ensure the whole dentinal equivalent stiffness is not loss, the porosity should get some value while the Ep/Ei is certain. Thus, PTD prevents the stress concentration around DTs and reduces the risk of DTs failure. Mechanically, the overall role of PTD appears to enhance the stiffness of the dentine composite structure. These results provide some new and significant insights into the biological evolution of the optimal design for the porous dentine microstructure. These findings on the biological microstructure design of dentine materials are applicable to other engineering structural designs aimed at increasing the overall structural strength. [ABSTRACT FROM AUTHOR]

During eating, the teeth usually endure the sharply temperature changes because of different foods. It is of importance to investigate the heat transfer and heat dissipation behavior of the dentino–enamel junction (DEJ) of human tooth since dentine and enamel have different thermophysical properties. The spatial and temporal temperature distributions on the enamel, dentine, and pulpal chamber of both the human tooth and its discontinuous boundaries, were measured using infrared thermography using a stepped temperature increase on the outer boundary of enamel crowns. The thermal diffusivities for enamel and dentine were deduced from the time dependent temperature change at the enamel and dentine layers. The thermal conductivities for enamel and dentine were calculated to be 0.81 Wm-1K-1 and 0.48 Wm-1K-1 respectively. The observed temperature discontinuities across the interfaces between enamel, dentine and pulp-chamber layers were due to the difference of thermal conductivities at interfaces rather than to the phase transformation. The temperature gradient distributes continuously across the enamel and dentine layers and their junction below a temperature of 42°C, whilst a negative thermal resistance is observed at interfaces above 42°C. These results suggest that the microstructure of the dentin-enamel junction (DEJ) junction play an important role in tooth heat transfer and protects the pulp from heat damage. [ABSTRACT FROM AUTHOR]

Abstract: Constant potential polarization approach was used to investigate the grooving corrosion performance of electric resistance welded oil well casings of J55 steels with different carbon content. The grooving corrosion sensitivity coefficient, α, depends intensively on the carbon content, microstructure of the steels and post-weld heat treatment. The steel with higher carbon content and fibrous pearlitic microstructure has higher grooving corrosion susceptibility. Post-weld heat treatment is shown to decrease the α value to some extent. The test solution and temperature have no apparent effects on the grooving corrosion sensitivity coefficient. The reasons for the grooving corrosion are discussed from the microstructure. [Copyright &y& Elsevier]

Abstract: The characteristics of grooving corrosion of oil coiled tubes by electric resistance welding were investigated by using electrochemical polarization tests and an immersed corrosion test. The welded tube exhibited severe localized corrosion in the welding zone. The post-weld heat treatments reduced the sensitivity of grooving corrosion. A corrosion groove occurred at the fusion line. The local heat treatment for the welding zone at 930°C adding the whole heat treatment for tubes at 690°C was beneficial to improve the resistance to the grooving corrosion. The reasons of the grooving corrosion were discussed from the microstructures and chemical compositions of the weld. [Copyright &y& Elsevier]

Using normal and shear rigid coefficients of intact rock and fracture plane, rigidly normal, shear equivalent rigid coefficients of fissure rock mass are conducted. On the basis of hypotheses of small displacement of rock mass, principle of superposition, irrelevance of strength parameters C and ϕ and Coulomb theory, formulas to calculate equivalent strength parameters C and ϕ of equivalent continuous mass from fissured rock mass with anchor piles are given. The achievement is extremely valuable in integral stability analysis of the rock mass slope and important in promoting the research of the rock mass's constitutive relation. [ABSTRACT FROM AUTHOR]

Ni60 cladding layers added with different amounts of rare-earth CeO 2 , Y 2 O 3 , and La 2 O 3 were prepared on the surface of 6063 aluminum alloys through laser cladding. The effects of such cladding layers on the macroscopic morphology, section morphology, micro-hardness, phase composition, microstructure, and composition distribution of the laser clad Ni-based coating were investigated by performing metallographic microscopy, X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and micro-hardness test. Cladding layers with the optimum rare-earth contents were 4% CeO 2 + Ni60 cladding layer, 5% Y 2 O 3 + Ni60 cladding layer, and 5% La 2 O 3 +Ni60 cladding layer. The main phase composition of the cladding layers included β-NiAl (Cr), Al 3 Ni, AlNi 3 , and Al. The Ni60 cladding layers added with rare-earth oxides produced a chemical reaction that was involved in the cladding process to form stable rare-earth compounds. Ni60 cladding layers added with 4% CeO 2 , 5% Y 2 O 3 , and 5% La 2 O 3 were preferable over those without rare-earth oxides, as the former displayed smoother micro-morphologies without obvious pores and cracks. The dendritic structures of the Ni60 cladding layers were coarse; moreover, many grain segregations that were accompanied by a large number of pores were observed in the local area. By contrast, the Ni60 cladding layers added with rare-earth oxides displayed compact dendritic structures, and the grains were obviously refined. The hardness of the cladding layers from the surface to the substrate was gradually decreased as the cladding layer depth increased. Compared with Ni60 cladding layer, the transitions of Ni, Al, Cr, and other elements in the Ni60 cladding layers added with different amounts of CeO 2 , Y 2 O 3 , and La 2 O 3 were became more observable with increasing depth, and the dilution rate of the cladding layer was reduced. [ABSTRACT FROM AUTHOR]

A series of 2.1 GHz surface acoustic wave filters with Al/Ti/Cu/Ti four-layer electrode using different Cu thickness were fabricated. Power durability test show an improvement from 24.5 dBm to 28 dBm by electrode with Al (111 nm)/Ti (5 nm)/Cu (15 nm)/Ti (5 nm) to widely used Al (155 nm)/Ti (5 nm). The different frequency response, electrode morphologies before and after power durability test indicate different failure mechanism of these samples. By checking the microstructures and distribution of elements in those conditions, the enhanced power durability can be attributed to: 1) using of Cu layer, 2) fine grain strengthening, 3) solution strengthening. Concurrently, Increased resistance of electrode induced by electrode structure design and atoms diffusion will deteriorate filter performance and accelerate atoms migration. In this work Al (111 nm)/Ti (5 nm)/Cu (15 nm)/Ti (5 nm) made a compromise in the above factors and achieved higher resistance to acoustomigration, which is promising for higher power surface acoustic wave filters. [ABSTRACT FROM AUTHOR]

Abstract: This study explores the potential of microstructured hollow fiber designs to enhance process performance in a direct contact membrane distillation (DCMD) system. Hollow fibers with 10 different geometries (wavy- and gear-shaped cross sections) were evaluated. A series of three-dimensional computational fluid dynamic (CFD) simulations were carried out to investigate their capability in terms of depolarizing the buildup of liquid boundary layers, thus improving water productivity. Analyses of heat and mass transfer as well as the flow-field distribution in respective MD modules were obtained. It was found that the enhancement of the heat-transfer coefficients, h f , was up to 4.5-fold for a module with a wavy fiber design 07 and an approximate 5.5-fold h p increase for a gear-shaped fiber design. The average temperature polarization coefficient and mass flux N m of the gear-shaped fiber module showed an improvement of 57% and 66%, respectively, over the original straight fiber design, followed by the wavy designs 07 and 08. The enhanced module performance was attributed to the improved hydrodynamics through the flow channels of various fiber geometries, which was confirmed by the visualization of flow-field and temperature profiles in CFD. Investigations of the fiber-length effect showed that the gear-shaped fiber modules exhibited the highest flux enhancement of 57–65% with the same length, compared to the modules with original straight and wavy fibers. In addition, the gear-shaped fiber module is very sensitive to feed velocity changes. Therefore, employing a smart microstructured design on the membrane surface would bring in a significant improvement under adverse flow conditions. Moreover, the computed water production and hydraulic energy consumption (HEC) among the modules with various fiber geometries were compared. With 1.9-fold surface area increase per unit volume, the gear-shaped fiber configuration had the highest water production but the lowest HEC, followed by wavy designs 07 and 08. [Copyright &y& Elsevier]

The effect of TiN addition on the high temperature oxidation behavior of Ti-Al-Cr coating was investigated. Results revealed that the coating with 4 wt.% TiN addition exhibited superior oxidation resistance. The minimum mass gain after being oxidized at 850 ℃ was 0.56 mg/cm2, which was 40.1% less than that of the TiN-free coating. The mechanisms for TiN addition can enhance the high-temperature oxidation resistance of Ti-Al-Cr coating include the dispersed TiN resulting in more grain boundaries and prolonging the diffusion paths of oxygen and contributing to the generation of a protective CrAlN layer to diminish the inward oxygen diffusion, as well as facilitating the formation of the dense internal oxide layer Al 2 O 3 and Cr 2 O 3. [Display omitted] • Ti-Al-Cr coatings with TiN addition were fabricated on TC21 for the first time. • TiN addition can promote the formation of core-ring microstructure. • The addition of TiN in the Ti-Al-Cr coating decreased oxidation rate. • TiN addition can change the oxide scale of Ti-Al-Cr coating. • The presence of CrAlN phase inhibited the internal diffusion of O in the oxide scales. [ABSTRACT FROM AUTHOR]