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An Fe314 alloy cladding layer was prepared on EA4T steel by laser cladding. Scanning electronmicroscopy (SEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and anelectrochemical workstation were used to investigat...
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An Fe314 alloy cladding layer was prepared on EA4T steel by laser cladding. Scanning electronmicroscopy (SEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and anelectrochemical workstation were used to investigate the microstructure, phase composition, elementdistribution and corrosion resistance of the cladding layer. The results showed that the microstructure ofthe cladding layer is columnar crystal and equiaxial crystal, the interior of the cladding layer grains ismainly an austenite phase, and the intergranular precipitates mainly include Fe3C, FeB and Cr3C2. Thecloser the cladding zone is to the bonding zone, the lower the Cr element content and the higher the Feelement content. Compared with the substrate, the cladding layer has excellent corrosion resistance..
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Semi-empirical atom-atom potential energy calculations based on pairwise additive interactions are performed and, after applying the Born-Oppenheimer approximation to separate high frequency vibrational modes from low frequency or...
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Semi-empirical atom-atom potential energy calculations based on pairwise additive interactions are performed and, after applying the Born-Oppenheimer approximation to separate high frequency vibrational modes from low frequency orientational and translational modes, the infrared vibrational spectra of CO_2 and N_2O monomers trapped in an argon matrix at a temperature of 5 K are determined. It is shown that only a double substitutional site in argon can accommodate N_2O, whereas CO_2 is trapped in two distinct sites, of single and double substitutional types. The model shows that splitting of the degenerate ν_2 mode occurs for both molecules in the double site. In the ground electronic state, the vibrational frequency shifts due to the matrix and the vibrational transition moments for low-lying levels are determined using the contact transformation method, as used for gas phase calculations. Calculated energy levels compare well with observed ones and the theory also predicts some unobserved levels. Moreover, calculations show no significant changes in the dipole moments of both CO_2 and N_2O trapped molecules.
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The Ni-Cr-Fe metal powder was deposited on EA4T steel by laser cladding technology. The microstructure and chemical composition of the cladding layer were analyzed by optical microscopy (OM), scanning electron microscopy (SEM) and...
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The Ni-Cr-Fe metal powder was deposited on EA4T steel by laser cladding technology. The microstructure and chemical composition of the cladding layer were analyzed by optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The bonding ability between the cladding layer and the matrix was measured. The results showed that the bonding between the cladding layer and the EA4T steel was metallurgical bonding. The microstructure of cladding layer was composed of planar crystals, columnar crystals and dendrite, which consisted of Cr2Ni3, gamma phase, M23C6 and Ni3B phases. When the powder feeding speed reached 4 g/min, the upper bainite occurred in the heat affected zone (HAZ). Moreover, the tensile strength of the joint increased, while the yield strength and the ductility decreased.
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The aim of this paper is to prove common fixed point theorems inMenger spaces using implicit relation and common (E.A) like property.An example is derived to support our main result. We extend our resultto four finite families of ...
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The aim of this paper is to prove common fixed point theorems inMenger spaces using implicit relation and common (E.A) like property.An example is derived to support our main result. We extend our resultto four finite families of self mappings. As an application of our mainresult, we prove an integral type common fixed point theorem satisfyingψ-contraction condition in Menger space. Our results improve some recent results in Menger spaces.
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摘要 :Highlights?Fatigue crack growth curves of EA4T were measured for wide range of stress ratios.?Experimentally obtained crack closure function was compared with the NASGRO one.?Each of closure mechanisms were analysed and separated ...
展开Highlights?Fatigue crack growth curves of EA4T were measured for wide range of stress ratios.?Experimentally obtained crack closure function was compared with the NASGRO one.?Each of closure mechanisms were analysed and separated for the threshold area.?Oxide-induced crack closure has a large significance in normal atmosphere.?Threshold value of EA4T is much lower in dry air than in normal atmosphere.AbstractThe paper is focused on fatigue crack propagation in the threshold area of the EA4T railway axle steel. Railway axles represent one of the most critical components for safety of trains. The main aim of this paper is to describe fatigue crack closure mechanisms in EA4T, which significantly influence the threshold value – a crucial parameter for determination of residual fatigue lifetime of railway axles. Investigated fatigue crack closure mechanisms are: plasticity induced crack closure, roughness-induced crack closure and oxide-induced crack closure. One part of this paper is focused on comparison of crack closure determined by NASGRO relationship (including plasticity induced crack closure mechanism only) with the experimentally obtained one. Difference between these two approaches is explained by presence of roughness and oxide induced crack closure. Based on theoretical models different sources of fatigue crack closure mechanisms was separated and evaluated. The significance of oxide-induced crack closure was confirmed based on experimental measurement of fatigue crack propagation in low humidity air. Finally, the effect of a reduced threshold value in low-humidity air on residual fatigue lifetime of railway axles is demonstrated.]]>
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In this work, we have investigated the effect of martensite/bainite dual phase content on the mechanical properties of EA4T high-speed axle steel. For evaluation and control of the strength, ductility, and toughness of steel, the ...
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In this work, we have investigated the effect of martensite/bainite dual phase content on the mechanical properties of EA4T high-speed axle steel. For evaluation and control of the strength, ductility, and toughness of steel, the microstructure of lath martensite (LM) and granular bainite (GB) was clarified through an optical microscope (OM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). Besides, the tensile fracture morphology was studied by scanning electron microscopy (SEM). For this purpose, this study conducted a quantitative analysis of the LM and GB fractions using the Pro Imaging software-2018 of OM. The remarkable effect of the LM/GB structure on mechanical properties is discussed. The results have shown that by increasing the volume fraction of the GB structure, the LM structure is refined and its microhardness and strength are improved. Meanwhile, the micro strength of LM follows the Hall-Petch relationship with the lath martensite packet size. Subsequently, the mechanical property prediction model of EA4T steel based on the LM/GB content was established by regression analysis of all experiment dates. When the LM fraction in the steel is about 40-70%, a superior combination of strength, ductility, and toughness can be obtained in EA4T steel.
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This paper investigated the effects of quenching medium (5% salt water or 12.5% PAG solution) and tempering temperature (600 ℃ or 650 ℃) on microstructures, mechanical properties, and fatigue behavior (FB) of EA4T steel. Microst...
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This paper investigated the effects of quenching medium (5% salt water or 12.5% PAG solution) and tempering temperature (600 ℃ or 650 ℃) on microstructures, mechanical properties, and fatigue behavior (FB) of EA4T steel. Microstructures were characterized by OM, SEM, and EBSD techniques. Improved FB of samples was obtained with the quenching medium of 5% salt water followed by tempering at 600 ℃. The presence of refined grain size and the decreased volume fraction of lath bainite (LB) significantly improved the FB. Furthermore, the combined effects of grain size and LB volume fraction on FB were revealed.
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Abstract In this study, forged EA4T steel specimens are subjected to three quenching temperatures of 800, 860, and 900 °C. Microhardness tester, laser scanning confocal microscopy, and scanning electron microscopy (SEM) are emplo...
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Abstract In this study, forged EA4T steel specimens are subjected to three quenching temperatures of 800, 860, and 900 °C. Microhardness tester, laser scanning confocal microscopy, and scanning electron microscopy (SEM) are employed to measure microhardness, metallographic structure, and fatigue fracture characteristics, respectively. Heat treatment is found to be necessary to improve mechanical properties and fatigue behavior of initial forgings, and the effects of microstructure and defect are significant. Hence, considering variations of grain types and roughness between the initial forgings and heat-treated specimens, the fatigue property with defects are modified for roughness-affected axles by an improved KT diagram. The results indicate that the samples quenching at 860 °C achieved better fatigue performance due to the presence of fine polygonal ferrite (PF), bainite, as well as martensite. The fatigue life prediction error for the roughness-affected axle is between 16 and 18%. All of the fracture mechanism, grain size, and dislocation slip with different quenching temperatures affecting the fatigue performance are analyzed. Because the volume fraction of the martensite and bainite is significantly higher reaching 57.48% and more refined grains are obtained, the dislocation slip to the surface is delayed at the quenching temperature of 860 °C. Thus, the fatigue behavior is superior. Moreover, the yield strength increased by 22% compared to that of the initial forgings. Studies on the effect of the heat treatment process on fatigue behavior of EA4T steel contribute with a practical reference to the engineering application of high-speed rail axles.
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An EA4T steel billet was forged at the different initial forging temperatures (1050, 1150, and 1250 degrees C). The microstructure and fatigue fracture of forged samples were observed by laser scanning confocal microscopy and scan...
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An EA4T steel billet was forged at the different initial forging temperatures (1050, 1150, and 1250 degrees C). The microstructure and fatigue fracture of forged samples were observed by laser scanning confocal microscopy and scanning electron microscopy, respectively. The fatigue performance of samples forged at an initial forging temperature of 1250 degrees C was better owing to the presence of fine polygonal ferrite (PF). The difference in yield strength and ultimate tensile strength can be attributed to the average grain size of PF and acicular ferrite (AF) content, respectively. A relationship between the tensile strength and fatigue limit of EA4T steel is proposed. The mechanism of grain size and dislocation slip affecting the fatigue property was elucidated. Because the fine PF grains delayed the dislocations moving to the surface and inhibited the formation of intrusion and extrusion, premature cracks were not easily produced. This contributed to excellent fatigue behavior. Additionally, the pearlite colonies and fine PF delayed the crack growth rate and changed the crack propagation path. Studies on fatigue behavior provided a foundation for quality control and engineering application of EA4T steel.
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