Search Results (18)

During the laser cladding process for composite coatings, significant differences exist in the physical and mechanical properties between the substrate and the composite coating materials. Therefore, a systematic analysis of the mechanical properties is necessary to mitigate issues such as cracking and deformation caused by performance mismatch. This study investigated the mechanical properties (microhardness, wear resistance, tensile strength) of composite coatings formed by laser cladding IN718 alloy onto an EA4T steel substrate. Given the critical influence of scanning strategies on cladding layer quality, this study also examined the relationship between the tensile direction and scanning direction. By analyzing mechanical responses under different orientations, it revealed the patterns of influence on tensile properties and anisotropy characteristics of the cladding layer, providing a theoretical basis and process guidance for achieving high-performance cladding layers. Tensile tests conducted at different angles on the IN718 cladding layer indicate that when a thin cladding layer is required, selecting a scanning speed direction parallel to the primary tensile direction yields superior results. Conversely, for applications demanding a thicker cladding layer, aligning the scanning direction perpendicular to the tensile direction better leverages the cladding layer’s performance. Full article

Laser cladding offers distinct advantages over traditional manufacturing methods, including low heat input, minimal dilution ratio, dense clad layers, and robust bonding. It is widely employed for surface strengthening of metals to enhance performance and repair failed components, thereby reducing material waste. This study investigates laser cladding repair of EA4T steel, focusing on examining the effects of laser power, scanning speed, and powder feed rate on melt pool dilution ratio and shape factor during cladding of IN718 material onto EA4T steel substrate. Orthogonal experiments were conducted to investigate the combined effects of different process parameters on dilution rate and shape factor. Optimal process parameters were determined by comprehensively evaluating melt pool cross-sectional morphology and internal defects. Based on this, theoretical lap calculations were performed, and the optimal theoretical lap ratio was obtained through experiments. Experiments indicated that the influence of process parameter variations on molten pool morphology parameters is not linear; the combined effects of all factors must be comprehensively considered. Full article

During the laser cladding process, the distribution of the temperature field directly influences the morphology, microstructure, and residual stress state of the cladding layer. However, the process involves transient characteristics of rapid heating and cooling, making it challenging to study temperature field variations directly through experimental methods. Therefore, numerical simulation has become a crucial tool for gaining a deeper understanding of the laser cladding mechanism, providing theoretical basis and guidance for optimizing process parameters. This study systematically integrates COMSOL Multiphysics coupling simulation with Jmatpro material thermal property data to perform simulations of temperature field evolution, melt pool flow behavior, and Marangoni effects during laser cladding of nickel-based alloy (IN718) onto an EA4T steel substrate. It highlights the influence patterns of different process parameters (e.g., laser power, scanning speed) on the temperature gradient and flow characteristics of the molten pool, providing an in-depth theoretical basis for understanding the formation mechanism of the molten pool and microstructure control. Full article

The electrochemical behavior and corrosion fatigue property of the surface-strengthened EA4T axle steel subjected to foreign object damage (FOD) is investigated in this study. It is found that the corrosion resistance can be enhanced after being impacted by the foreign object due to the introduced hardening layer. Specifically, compared to the smoothed sample, the 167 m/s sample exhibited a 13.88% higher corrosion potential (E_corr) and a 67.61% lower current density (i_corr). The facture surface demonstrates that the corrosion pits on the surface are the main crack initiation location for the smoothed specimens. In contrast, for the surface-damaged specimens, cracks initiate around the crater. The foreign object impact speed has a significant influence on the corrosion fatigue strength; specifically, the faster the impact velocity, the greater the surface damage of the axle specimen, and the shorter its fatigue life at the same stress level. To address the combined influence of size effect and surface defects on fatigue performance, we constructed an improved Kitagawa–Takahashi (KT) diagram by incorporating the theoretical corrosion fatigue limit of full-scale axles with a surface damage of 270 MPa based on conditional probability density function (CPDF). Comparative analysis demonstrates that the revised KT diagram defines a narrower yet more conservative fatigue loading safety zone than the standard KT diagram. This refinement enhances reliability in practical applications where surface imperfections and scale effects dominate failure mechanisms. Full article

CuMn_1−xMg_xO₂ (x = 0–0.06) polycrystalline samples were prepared using the hydrothermal method at T = 100 °C for 24 h in Teflon-line stainless steel autoclaves. The samples were crystallized, forming crednerite structures (C2/m space group), and the Mg²⁺ substitution onto the Mn³⁺ site induced small changes in the unit cell parameters and volume. Based on complex impedance measurements made between 20 Hz and 2 MHz, at different concentrations of Mg ions (x), the electrical conductivity (σ), the electric modulus (M), and the complex dielectric permittivity (ε) were determined. The conductivity spectrum, σ(f, x), follows the Jonscher universal law and enables the determination of the static conductivity (σ_DC) of the samples. The results showed that, when increasing the concentration x from 0 to 6%, σ_DC varied from 15.36 × 10⁻⁵ S/m to 16.42 × 10⁻⁵ S/m, with a minimum of 4.85 × 10⁻⁵ S/m found at a concentration of x = 4%. Using variable range hopping (VRH) and correlated barrier hopping (CBH) theoretical models, the electrical mechanism in the samples was explained. The band gap energy (W_m), charge carrier mobility (μ), number density (N_C) of effective charge carriers, and hopping frequency (ω_h) were evaluated at different concentrations (x) of substitution with Mg. In addition, using measurements of the temperature dependence of σ_DC(T) between 300 and 400 K, the thermal activation energy (E_A) of the samples was evaluated. Additionally, the dielectric behavior of the samples was explained by the interfacial relaxation process. This knowledge of the electrical properties of the CuMn_1−xMgxO₂ (x = 0–0.06) polycrystalline crednerite is of interest for their use in photocatalytic, electronic, or other applications. Full article

This paper presents studies on the influence of the chemical structure of (meth)acrylic monomers on the properties of powder coatings based on polyacrylate resins. For this purpose, a wide range of monomers were selected—2-hydroxyethyl methacrylate (HEMA), methyl methacrylate (MMA), n-butyl acrylate (nBA), tert-butyl acrylate (tBA), dodecyl acrylate (DA), ethyl acrylate (EA) and benzyl acrylate (BAZ)—for the synthesis of the polyacrylate resin. The average molecular mass and molecular mass distribution of the synthesized resins were measured by gel permeation chromatography (GPC). The glass transition temperature (T_g) and viscosity of polyacrylate resins were determined by using differential scanning calorimetry (DSC) and a Brookfield viscometer. These parameters were necessary to obtain information about storage stability and behavior during the application of powder clear coatings. Additionally, DSC was also used to checked the course of the low-temperature curing reaction between the hydroxyl group contained in the polyacrylate resin and the blocked polyisocyanate group derived from a commercial agent such as Vestanat B 1358/100. The properties of the cured powder clear coatings were tested, such as: roughness, gloss, adhesion to the steel surface, hardness, cupping, scratch resistance, impact resistance and water contact angle. The best powder clear coating based on the polyacrylate resin L_HEMA/6MMA/0.5nBA/0.5DA was characterized as having good scratch resistance (550 g) and adhesion to the steel surface, a high water contact angle (93.53 deg.) and excellent cupping (13.38 mm). Moreover, its crosslinking density (CD) and its thermal stability was checked by using dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). Full article

The microstructure and mechanical properties of electrically assisted brazing (EA-brazing) joints of aluminum alloy 6061-t6 (AA6061-t6) and S45C steel are experimentally investigated. During the EA-brazing process, an electric current is directly applied to the cylindrical specimen assembly (S45C and AA6061-t6) and fillers of 88% Al and 12% Si (in the middle of the specimen assembly). The temperature of the specimen assembly rises rapidly to the melting point of the filler and remains nearly constant for a period of time using a pulsed electric current. Two types of EA-brazing joints are fabricated, namely Joint-0s (no temperature holding time) and Joint-12s (12 s temperature holding time). The characteristics of the intermetallic compounds (IMCs) formed at the EA-brazing joint interface are analyzed using scanning electron microscopy and energy dispersive spectrometer. Compared to Joint-0s, the Fe-rich IMCs (FeAl) are observed at the interface of Joint-12s due to the 12 s temperature holding time. In addition, the microstructural analysis shows that the thickness of the diffusion layer increases with increasing temperature holding time. The mechanical properties of the EA-brazing joints are evaluated using bending tests. The results of the mechanical test show that the strength of Joint-12s is higher than that of Joint-0s. Full article

In order to reveal the dislocation evolution law of body-centered cubic axle steel EA4T during cyclic deformation and provide an experimental basis for the subsequent construction of cyclic constitutive models based on microscopic physical mechanisms, macroscopic deformation experiments were first conducted on axle steel EA4T, including monotonic tensile experiments under different deformation amounts, symmetric strain cycling experiments under a different number of cycles, and ratcheting deformation experiments under a different number of cycles. Then, systematic observations of different samples at different deformation stages were conducted using a Transmission Electron Microscope (TEM) to investigate the dislocation configuration and evolution during strain cycling and ratcheting deformation. The observed results show that the dislocation evolution law of axle steel EA4T during the uniaxial tensile experiment, symmetrical strain cycling, and ratcheting deformation is basically the same, and the dislocation density increases with the increase in plastic deformation and number of cycles. The dislocation configuration gradually develops from low-density dislocation configurations such as dislocation lines and dislocation pileups to high-density dislocation configurations such as severe dislocation tangles and dislocation walls. The microscopic mechanism of the uniaxial ratcheting evolution of axle steel EA4T can be qualitatively explained by the dislocation configuration and evolution. Full article

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. Full article

EA4T steel has been widely used in the manufacture of railway axles. Laser cladding remanufacturing technology has been used to repair railway axles, and the failure behaviors of railway axles has been studied. In this work, a class of original FeCrNiMo alloy layers that contain rare-earth elements was successfully fabricated through a laser cladding technique on EA4T steel substrates. The microstructure and elemental distribution of the cladding layers were analyzed through scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron probe microanalysis (EPMA). Simultaneously, the microhardness, bond strength and fatigue properties of different samples were determined. The results indicated that the phase composition of the cladding layer was mainly martensite. The grains in the cladding layer were gradually refined with an increase in the distance from the interface, and the chemical composition distribution was more uniform. At the same time, the bonding property of the cladding layer and matrix was good, and the fatigue strength of the sample was improved. Full article

Cold-rolled EA4T steel was heat-treated by inter-critical holding at 755 °C for 90, 120, 180, and 240 s, respectively, and then quenching in water. The tensile testing results of the EA4T specimens show an evident transition from the discontinuous yielding to the continuous yielding of the steel specimens by prolonging the holding time. A novel relationship between the discontinuous yielding behavior of tensile-deformed steel specimens and the carbide size was proposed based on experimental results and Cottrell’s theory. The model may provide a new clue for avoiding discontinuous yielding and improving mechanical properties of metals with static strain aging behaviors. Full article

In this paper, a series of experimental investigations was performed on full-scale railway axles to analyze the fatigue crack growth behavior of EA4T steel under load spectrum derived from real operating conditions. The experimental results were compared to life predictions carried out adopting two models: (i) the conventional Nasgro equation and (ii) the cyclic R-curve concept implemented in the Modified Nasgro equation for describing the crack growth behavior of an arbitrary crack length. The results show that the life predictions performed by means of the Modified Nasgro equation coincide well with the experimental results with an underestimation of the residual lifetime less than 32%, while the traditional Nasgro equation leads to significant overestimation (≈120%) of the residual lifetime for load spectra close to the in service scenario. Full article

Underload cycles with small load amplitudes below the fatigue crack growth threshold are dominantly considered as insignificant cycles without any influence on fatigue lifespan of engineering structural components. However, this paper shows that in some cases these underload cycles can retard the consequent crack propagation quite significantly. This phenomenon is a consequence of oxide-induced crack closure development during cyclic loading below the threshold. The experimentally described effect of fatigue crack growth retardation was supported by measurement of the width and the thickness of the oxide debris layer using the EDS technique and localized FIB cuts, respectively. Both the retardation effect and the amount of oxide debris were larger for higher number and larger amplitudes of the applied underload cycles. Crack closure measurement revealed a gradual increase of the closure level during underload cycling. Specimens tested in low air humidity, as well as specimens left with the crack open for the same time as that needed for application of the underload cycles, revealed no retardation effect. The results can improve our understanding of environmental effects on fatigue crack propagation and understanding the differences between the results of laboratory testing and the fatigue lives of components in service. Full article

Fatigue property is a key evaluation index for the service reliability of railway axle. In this work, the effect of ultrasonic surface rolling processing (USRP) on the surface characteristic and fatigue property was investigated in an EA4T axle steel used on high speed trains by several characterization techniques and the staircase method fatigue testing. The surface characteristics were initially studied in EA4T axle steel under different static loads of 1.0 kN, 1.5 kN and 2.0 kN, and served as the important USRP parameter. It was found that the larger static load greatly improved the surface microstructure, microhardness and compressive residual stress, but also increased the surface roughness. Furthermore, the rotating bending fatigue endurance limit of the USRP specimen with a static load of 1.5 kN was obviously enhanced by ~14% (from ~352 MPa to ~401 MPa) relative to the untreated specimen. The enhanced fatigue limit induced by USRP was attributed to the synergistic effect of the grain refinement, as evidenced by transmission electron microscope (TEM) observation, work-hardening, the increased compressive residual stress and the reduced surface roughness. Moreover, the fatigue limit of the USRP specimen was ~4% higher than that of the rolling specimen with turning off the ultrasonic system, ~386 MPa, which showed that the role of the ultrasonic impact could enhance the fatigue property. These findings demonstrate the validity of this technique in modifying the surface characteristics and thus improving the fatigue resistance of axle material, further ensuring its service safety and reliability. Full article

A comparative study was conducted to reveal the effect of microstructure on hydrogen permeation in the EA4T and 30CrNiMoV12 railway axle steels. Unlike the EA4T with its sorbite structure, 30CrNiMoV12 steel shows a typical tempered martensitic structure, in which a large number of fine, short, rod-like, and spherical carbides are uniformly dispersed at boundaries and inside laths. More importantly, this structure possesses plentifully strong hydrogen traps, such as nanosized Cr₇C₃, Mo₂C, VC, and V₄C₃, thus resulting in a high density of trapping sites (N = 1.17 × 10²² cm⁻³). The hydrogen permeation experiments further demonstrated that, compared to EA4T, the 30CrNiMoV12 steel not only delivered minimally effective hydrogen diffusivity but also had a high hydrogen concentration. The activation energy for hydrogen diffusion of the 30CrNiMoV12 steel was greatly increased from 23.27 ± 1.94 of EA4T to 47.82 ± 2.14 kJ mol⁻¹. Full article