Search Results (53)

M50 steel is widely used in the manufacturing of high-end bearing components for aero-engine shafts, where an excellent surface performance is required to withstand harsh service conditions. In this study, plasma carburizing at different temperatures varying from 410 to 570 °C was performed on pre-nitrided M50 steel to investigate the influence of the temperature on the structural evolution and mechanical behavior of the self-lubricating functional layer. The microstructure, phase composition, hardness, and wear resistance of the carburized samples were fully characterized using scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Raman spectroscopy, a nano-indenter, and other analytical techniques. The carbon-rich film with nano-domains contains a significant amount of sp³ bonds at low carburizing temperatures, exhibiting a Diamond-like carbon (DLC) film character. With the rise in the carburizing temperature, the initially distinct interface between the carbon-rich film and the compound layer gradually disappears as the nitrides are progressively replaced by carbides; the sp³ bond of the film is decreased, which reduces the hardness and wear resistance. Samples carburized at 490 °C with a homogeneous surface layer consisting of DLC film and a compound layer showed a low friction coefficient (about 0.22) and a 60% reduction in the wear rate compared with the nitrided specimen. The formation of a surface carbon-enriched layer also plays a role in avoiding oxidative wear. Full article

For efficient utilization of carbide slag (CS) waste to high-value building materials, in this study, CS and ground granulated blast furnace slag (GBFS) were used as primary raw materials to prepare alkali-activated cementitious systems under strong alkaline excitation. Multiscale mechanisms involving macroscopic mechanical property development were investigated. Microstructural characterization elucidated how raw material composition affected mineral crystal formation and transformation while revealing enhancement mechanisms governing micro-gel network structure formation and evolution dynamics. The results indicate that excessive calcium components coupled with deficient Si–Al sources in CS severely inhibit the formation of C-S-H and C-A-S-H gel phases, consequently impeding mechanical performance development. Also, GBFS incorporation offsets inherent silicon–aluminum deficiencies. Active [SiO₄]⁴⁻ and [AlO₄]⁵⁻ released from GBFS drive polycondensation reactions toward advanced polymerization states. Compressive strength has a nonlinear growth kinetics characterized by rapid initial ascent, followed by asymptotic plateauing as GBFS content increases. Optimal comprehensive performance emerges at a 5:5 GBFS-to-CS mass ratio, where 28d compressive strength reaches 47.5 MPa. Full article

This study investigates the hydrothermal synthesis of calcium silicate hydrate (C-S-H) from photovoltaic (PV) waste glass and carbide sludge as a strategy for resource recovery and sustainable chromium removal from wastewater. Waste-derived precursors were co-ground, blended at controlled Ca/Si molar ratios (0.8, 1.0, 1.2), and hydrothermally treated at 180 °C for 96 h to yield C-S-H with tunable morphology and crystallinity. Comprehensive characterization using XRD, FT-IR, SEM-EDX, and UV-Vis spectroscopy revealed that a Ca/Si ratio of 1.0 produced a well-ordered tobermorite/xonotlite structure with a high surface area and fibrous network, which is optimal for adsorption. Batch adsorption experiments showed that this material achieved rapid and efficient Cr(III) removal, exceeding 90% uptake within 9 h through a combination of surface complexation, ion exchange (Ca²⁺/Na⁺ ↔ Cr³⁺), and precipitation of CaCrO₄ phases. Morphological and structural evolution during adsorption was confirmed by SEM, FT-IR, and XRD, while EDX mapping established the progressive incorporation of Cr into the C-S-H matrix. These findings highlight the viability of upcycling industrial waste into advanced C-S-H sorbents for heavy metal remediation. Further work is recommended to address sorbent regeneration, long-term stability, and application to other contaminants, providing a foundation for circular approaches in advanced wastewater treatment. Full article

The microstructural evolution and mechanical properties of WWER 440 steam generator steel GOST 22K after long-term operation were thoroughly examined in this study. The samples were taken directly from a steam generator using the small punch test method. The uniqueness of these samples lies in the fact that they were real operating materials used in a nuclear power plant with different years of operation. The microstructure was characterized using optical microscopy and transmission electron microscopy supplemented by selective electron diffraction and semi-quantitative chemical microanalysis. It was found that with the prolongation of the operation time of the steam generator, the density of carbides increased slightly, which was reflected in a decrease in the mean distance between particles, but these differences were very small, which indicates the microstructural stability of GOST 22K steel. The stability of this steel was also confirmed by measuring its mechanical properties, which changed only minimally depending on the years of operation. The tensile strength values were in the range of 508 to 579 MPa. In the case of the ductile-to-brittle transition temperature (DBTT), a slight increase was found after 6 years of operation. The DBTT did not change significantly with subsequent operation. Full article

The phase composition and morphological characteristics of eutectic carbides are key factors affecting the wear resistance and fatigue life of high-speed steel. In this study, a combination of experimental characterization and thermodynamic calculations was used to systematically reveal the dynamic regulation mechanism of cooling rate on eutectic carbides in M2Al high-speed steel. The results indicate that within a cooling rate range of 5 to 225 °C/min, the steel always contains a small amount of face-centered cubic-structured MC-type eutectic carbides and a large number of hexagonal close-packed structured M₂C-type eutectic carbides. The three-dimensional morphology of MC-type eutectic carbides is smooth and rod-like, and is insensitive to the cooling rate, while the three-dimensional morphology of M₂C-type eutectic carbides evolves from lamellar to dendritic with an increasing cooling rate. The increase in cooling rate significantly reduces the average size of eutectic carbides, increases the total area fraction, and improves the distribution uniformity. Additionally, the increase in cooling rate also promotes the significant refinement of secondary dendrites in M2Al high-speed steel, and the relationship between secondary dendrite arm spacing and cooling rate is ${\lambda }_{SDAS}=149.42\cdot {C_R}^{-0.39}$. Finally, combining thermodynamic calculations with kinetic analysis, this study found that the formation of eutectic carbides is dominated by the segregation of elements such as V, Mo, and C during the final stage of solidification, while the chemical composition and three-dimensional morphological evolution of M₂C-type eutectic carbides are synergistically controlled by the diffusion and competitive growth of elements such as W, Mo, and C in austenite. This study provides a theoretical basis for the solidification process and eutectic carbide control of M2Al high-speed steel. Full article

In this study, laser melting experiments of Ni60/WC composite powder coatings were carried out using a laser, and the surface morphology and microstructure of the coatings were analyzed using a scanning electron microscope (SEM) coupled with energy dispersive X-ray spectroscopy (EDS). In addition, hardness testing equipment was used to assess the hardness of the coatings and an electrochemical workstation was used to characterize their corrosion resistance. The key findings demonstrate substantial variations in coating performance based on remelting parameters. The coatings processed without secondary laser remelting exhibited an average hardness of 501.36 (standard deviation 154.46) HV_0.2, a self-corrosion potential of −0.039 V, and a self-corrosion current density of 8.11 × 10⁻⁴ A/cm². In contrast, some coatings were subjected to secondary remelting at 800 mm/min (S 800). The laser is used to scan the surface of the cladding with the laser on the surface of the cladding, and the speed is the feed rate of the laser scanning. XRD analysis revealed intensified main peaks, indicative of elevated solid solution and carbide content. SEM micrographs displayed fishbone-like and feather-like morphologies, with the hardness increasing to 622.98 (standard deviation 9.60) HV_0.2 and the corrosion metrics improving to −0.038 V and 2.86 × 10⁻⁵ A/cm². In contrast, coatings remelted at 600 mm/min (S600) exhibited broader but less intense XDR peaks, alongside diminished reticulation in SEM imagery. These samples demonstrated marginally lower hardness 599.91 (standard deviation 8.35) HV_0.2 but superior corrosion resistance, with a self-corrosion potential of −0.012 V and current density of 2.64 × 10⁻⁵ A/cm². The results underscore the critical influence of laser scanning velocity and remelting frequency on microstructural evolution, mechanical strength, and electrochemical stability. Enhanced hardness correlates with refined microstructural features, while enhanced corrosion resistance arises from reduced defect density and stabilized electrochemical activity. Full article

To address the issues of the low pozzolanic activity and high pollution potential of red mud (RM), this study utilizes different industrial solid wastes to synergistically enhance the physicochemical properties of red mud-based filling materials. The compressive strengths of red mud-based filling materials activated by three types of solid wastes—desulfurized gypsum (DG), carbide slag (CS), and steel slag (SS)—were compared, revealing the differences in their effects on the physicochemical properties of the materials. The results showed that DG significantly enhanced the compressive strength of the backfill material. The composite system composed of 65.8% RM, 18.8% FA, 9.4% cement, and 6% DG achieved a compressive strength of 7.36 MPa after 28 days of curing, demonstrating a 97.8% increase compared to the control group. Techniques such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and Brunauer–Emmett–Teller (BET) analysis were employed to characterize the microstructural evolution of the red mud-based filling materials activated by different solid wastes. This study investigated the differences in the pore structure, microscopic morphology, and chemical composition of the materials containing different solid wastes. The results indicated that DG effectively promotes the formation of ettringite and C(-A)-S-H gel, optimizes the pore structure of the filling materials, and forms a dense matrix, thereby enhancing the stiffness and strength of the materials. Additionally, the red mud-based filling materials developed in this study exhibit excellent environmental performance. This not only provides theoretical support for the development of red mud-based filling materials but also offers new insights for mine backfilling and the co-disposal of solid wastes. Full article

The formation of surface austenite leads to microstructural changes, causing grinding hardening. However, the effect of grinding mechanical stresses on surface austenitization remains unclear. Additionally, the mechanical properties of the metamorphic layer are crucial for studying grinding hardening. Therefore, in this study, the evolution of the microstructure and corresponding mechanical properties of the grinding surface in 8Cr4Mo4V steel was analyzed. The microstructure of the metamorphic layer was characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Physical simulation was employed to analyze the effect of mechanical compressive stress on the austenite transformation start temperature (Ac1). Dimensionless analysis, based on nanoindentation results, was conducted to study the mechanical properties of the metamorphic layer. The metamorphic layer in 8Cr4Mo4V steel consists of martensite, retained austenite, and undissolved carbides. The unresolved carbides are distributed within the cryptocrystalline martensite. Increasing the grinding depth and workpiece feed speed results in higher mechanical stress and temperature, which leads to a reduction in Ac1 and a higher content of austenite. The yield strength of the metamorphic layer is 2427 MPa, which is 427 MPa higher than that of the matrix, indicating obvious grinding hardening. Full article

A modified carbide-free bainite (CFB) steel has been developed, building on existing alloys for compatibility with commercial continuous annealing lines (CALs), featuring a low austenitization temperature and short overaging time. The microstructural features of such candidate CFB sheets are compared with those of conventional CFB steel sheets that require higher reheating temperatures and longer overaging times. The effects of annealing parameters such as reheating temperatures and overaging temperatures on phase transformation kinetics and microstructure evolution are presented. The annealing process was simulated in a Gleeble thermomechanical processing simulator, and the microstructural characterization was carried out using XRD, SEM, and EBSD. Reconstruction of parent austenite grains from EBSD data did not reveal any variant selection, regardless of changes in the austenitization temperature, overaging temperature, or carbon content. It was observed that the V1–V2 variant pairing is the most common at the lower overaging temperature for reheating at 950 °C; however, this pairing decreases as the isothermal overaging temperature increases, with variant pairings involving low misorientation boundaries—such as V1–V4 and V1–V8—becoming more frequent. Steels with higher carbon content exhibit no significant changes in their variant pairing, regardless of variations in the austenitizing or isothermal temperatures. The XRD results show that the retained austenite fraction is reduced by increasing the isothermal transformation temperature. Full article

Hydrogen is regarded as an ideal energy carrier to cope with the energy crisis and environmental problems due to its high energy density, cleanliness, and renewability. Although there are several primary methods of industrial hydrogen production, hydrogen evolution reaction (HER) is an efficient, eco-friendly, and sustainably green method for the preparation of hydrogen which has attracted considerable attention. However, this technique is characterized by slow reaction kinetics and high energy potential owing to lack of electrocatalysts with cost-effective and high performance which impedes its scale-up. To address this issue, various studies have focused on electrospun micro/nanofiber-based electrocatalysts for HER due to their excellent electron and mass transport, high specific surface area, as well as high porosity and flexibility. To further advance their development, recent progress of highly efficient HER electrospun electrocatalysts is reviewed. Initially, the characteristics of potential high-performance electrocatalysts for HER are elucidated. Subsequently, the advantages of utilizing electrospinning technology for the preparation of electrocatalysts are summarized. Then, the classification of electrospun micro/nanofiber-based electrocatalysts for HER are analyzed, including metal-based electrospun electrocatalyst (noble metals and alloys, transition metals, and alloys), metal–non-metal electrocatalysts (metal sulfide-based electrocatalysts, metal oxide-based electrocatalysts, metal phosphide-based electrocatalysts, metal nitride-based electrocatalysts, and metal carbide-based electrocatalysts), metal-free electrospun micro/nanofiber-based electrocatalysts, and hybrid electrospun micro/nanofiber-based electrocatalysts. Following this, enhancement strategies for electrospun micro/nanofiber-based electrocatalysts are discussed. Finally, current challenges and the future research directions of electrospun micro/nanofiber-based electrocatalysts for HER are concluded. Full article

Tool wear in machining is inevitable, and determining the precise moment to change the tool is challenging, as the tool transitions from the steady wear phase to the rapid wear phase, where wear accelerates significantly. If the tool is not replaced correctly, it can result in poor machining performance. On the other hand, changing the tool too early can lead to unnecessary downtime and increased tooling costs. This makes it critical to closely monitor tool wear and utilize predictive maintenance strategies, such as tool condition monitoring systems, to optimize tool life and maintain machining efficiency. Acoustic emission (AE) is a widely used technique for indirect monitoring. This study investigated the use of Short-Time Fourier Transform (STFT) for real-time monitoring of tool wear in machining AISI 4340 steel using carbide tools. The research aimed to identify specific wear mechanisms, such as abrasive and adhesive ones, through AE signals, providing deeper insights into the temporal evolution of these phenomena. Machining tests were conducted at various cutting speeds, feed rates, and depths of cut, utilizing uncoated and AlCrN-coated carbide tools. AE signals were acquired and analyzed using STFT to isolate wear-related signals from those associated with material deformation. The results showed that STFT effectively identified key frequencies related to wear, such as abrasive between 200 and 1000 kHz and crack propagation between 350 and 550 kHz, enabling a precise characterization of wear mechanisms. Comparative analysis of uncoated and coated tools revealed that AlCrN coatings reduced tool wear extending tool life, demonstrating superior performance in severe cutting conditions. The findings highlight the potential of STFT as a robust tool for monitoring tool wear in machining operations, offering valuable information to optimize tool maintenance and enhance machining efficiency. Full article

The evolution of the microstructural and mechanical properties of alloy 617B during long-term service on a key-component test platform at 700 °C was systematically investigated. The precipitation behavior and size changes of the M₂₃C₆ and γ′ phases were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that carbide M₂₃C₆ precipitated in the form of discontinuous particles, plates, or needles at grain boundaries and within grains, while the γ′ phase had a spherical shape and was distributed in a dispersed manner. With prolonged service time, both the M₂₃C₆ and γ′ phases gradually coarsened. After 24,000 h of service, the yield strength, tensile strength, and Brinell hardness of alloy 617B significantly increased; however, the impact toughness decreased, accompanied by intergranular embrittlement. The increase in precipitate volume fraction and its contribution to the strength of the alloy were evaluated by a precipitation strengthening model. The coarsening of M₂₃C₆ was identified as the main cause of embrittlement. The findings of this study provide important experimental data and theoretical support for the stability of 617B alloys under long-term high-temperature service conditions. Full article

This paper deals with the development and characterization of an Inconel 625 (IN625) reinforced with 2 wt.% of sub-micrometrical TiC particles produced by the laser powder bed fusion (LPBF) process. IN625 and IN625 2 wt.% TiC microstructural evolution was evaluated in the as-built, solution-annealed (2 h at 1150 °C), and prolonged heat-treated (2 h at 1150 °C + 100 h at 1000 °C) conditions. The IN625 and IN625 + TiC samples were successfully produced with low residual porosity (<0.15%). In the as-built conditions, both materials developed mainly columnar grains elongated to the building direction with melt pools, fine dendric structures, and small fractions of recrystallized grains. Some TiC segregations were observed in the composite, preferentially located at the melt pool boundaries. The heat treatments led to a different microstructural evolution between the base alloy and the composite. After solution annealing, the IN625 alloy was subjected to full recrystallization with a drastic reduction in hardness. Afterward, the prolonged thermal exposures for 100 h at 1000 °C provoked the formation of carbides, increasing the hardness. On the contrary, the composite retained the as-built microstructure with columnar grains in the solution-annealed and prolonged heat-treated conditions, revealing a limited formation and growth of carbides, thus resulting in a reduced hardness variation. The addition of TiC inside the IN625 enhanced the microstructural stability of the composite, preventing the recrystallization and the growth of phases occurring under prolonged thermal exposures. The current study therefore reported the effect of TiC particles on the microstructural stabilization of LPBFed IN625, with a peculiar focus on the prolonged thermal exposure at 1000 °C. Full article

Tailor-made materials used for advanced applications are nowadays of great research interest in various industrial and technological fields, ranging from aerospace and automotive applications to consumer goods and biomedical components. In the present research, Inconel 718 superalloy specimens were fabricated by the selective laser melting (SLM) technique. Structural characterization of the 3D-printed samples showed that they consisted of γ solid solution along with spherical carbide particles. To explore the applicability of these materials in abrasive tribological applications, reciprocating sliding tests were performed under dry conditions versus an Al₂O₃ counter-body. A 3D representation (triboscopy) of the tangential force during each sliding cycle was carried out in order to obtain better insight on the evolution of friction and to visualize localized tribological phenomena. Quantification of wear was performed with confocal microscopy and the wear mechanisms were analyzed with SEM and EDS techniques. Furthermore, the effect of surface finishing (as-printed and polished) on friction and wear were also investigated, and a comparison with other industrial materials is also included to evaluate the applicability of these alloys. The results indicated that surface finishing had an effect on friction during the run-in stage, whereas in steady-state conditions, no significant differences were observed between the as-printed and polished specimens. In all cases, the main wear mechanisms observed were a mixture of two-body and three-body abrasion, along with oxidative wear (indicated by the formation of an oxide-based tribo-layer). Full article

Cylinder liners, considered a crucial component of internal combustion (IC) engines, often require excellent mechanical properties to ensure optimal engine performance under elevated temperatures, pressures, and varying loads. In this work, a new low-alloy cylinder liner, incorporating a low content of molybdenum, copper, and chromium into gray cast iron, was fabricated using a centrifugal casting process. Subsequently, the heat treatment processes were designed to achieve bainite microstructures in the cylinder liner through rapid air cooling, isothermal transformation, and tempering. The effects of different air-cooling rates and tempering temperatures on the microstructure evolution and mechanical properties of cylinder liner were investigated. The results revealed that during the supercooled austenite transformation process, rapid air cooling at a rate of 14.5–23.3 °C/s can effectively bypass the formation of pearlitic structures and directly induce the formation of bainite structures. Once the temperature exceeded 480–520 °C, hardness and tensile strength increased with the temperature increase owing to the enhancement of the lower bainite content, the reduction of residual austenite, and the precipitation of the fine hard carbides in the matrix. With temperatures above 520–550 °C, the carbide and lower bainite organization coarsened, thereby reducing the hardness and tensile strength of the material. Therefore, the optimal heat treatment parameters were rapid cooling at 14.5–23.3 °C/s rate to obtain bainite, and tempering of 480–520 °C for finer and more uniform bainite. In addition, the results of the characterization of the mechanical properties of the cylinder liner after heat treatment showed that the hardness, tensile strength, and wear resistance were improved with the refinement of the bainite. Full article