Search Results (50)

This study investigates the thermal response and surface modification of low-carbon manganese-alloyed 20GL steel during electrolytic plasma hardening. The objective was to evaluate the feasibility of surface hardening 20GL steel—traditionally considered difficult to quench—by combining high-rate surface heating with rapid cooling in an electrolyte medium. To achieve this, a transient two-dimensional heat conduction model was developed to simulate temperature evolution in the steel sample under three voltage regimes. The model accounted for dynamic thermal properties and non-linear boundary conditions, focusing on temperature gradients across the thickness. Experimental temperature measurements were obtained using a K-type thermocouple embedded at a depth of 2 mm, with corrections for sensor inertia based on exponential response behavior. A comparison between simulation and experiment was conducted, focusing on peak temperatures, heating and cooling rates, and the effective thermal penetration depth. Microhardness profiling and metallographic examination confirmed surface strengthening and structural refinement, which intensified with increasing voltage. Importantly, the study identified a critical cooling rate threshold of approximately 50 °C/s required to initiate martensitic transformation in 20GL steel. These findings provide a foundation for future optimization of quenching strategies for low-carbon steels by offering insight into the interplay between thermal fluxes, surface kinetics, and process parameters. Full article

Recent progress in metal matrix composites (MMCs) has led to significant research efforts aimed at refining reinforcement methods and processing techniques and enhancing material properties. Incorporating reinforcements has notably improved both mechanical strength and tribological performance while addressing issues such as porosity and particle agglomeration. This study investigates the impact of copper reinforcement (1–4 wt.%) on the tribological characteristics of A356 alloy under both as-cast and heat-treated conditions. The process of heat treatment involved age hardening, where the composites were solution heat treated (SHT) at 535 °C for 2 h, followed by rapid quenching and aging at 100 °C and 200 °C. The results demonstrate that increasing the copper content enhances the composite’s mechanical properties. Specifically, heat treatment promoted the redistribution of the Al₂Cu intermetallic phase during peak aging, leading to improved hardness and wear resistance. Wear testing demonstrated that heat-treated composites exhibited significantly better wear resistance than their as-cast counterparts, with improvements of 50–60% under lower loads and 80–90% under higher loads. Among the tested samples, A356 alloy reinforced with 4 wt.% copper showed the lowest wear rate across all the applied loads, along with a reduced coefficient of friction and enhanced load-bearing capacity, minimizing material deformation. Additionally, aging at 100 °C resulted in the greatest hardness and the lowest wear rate in comparison to untreated A356 alloy. These findings underscore the viability of copper-reinforced A356 composites for applications demanding enhanced mechanical characteristics and wear resistance. Full article

In the automotive industry, structural components are often produced via press hardening, enabling rapid production and the use of ultra-high-strength steels. In this process, steels are heated to an austenitic state and are then formed and quenched in rapid succession. The initial steel that enters the press-hardening production line varies, where the microstructure is a result of previous production steps. This work was performed to investigate the possible effects of the initial microstructure on the final mechanical properties for rapidly quenched samples. Although the initial microstructure is transformed during austenitization, the steel can still be affected by its prior history. Steels with three different initial microstructures were evaluated, with only minor variations in chemical composition and thicknesses. The Lankford coefficients and the failure strains were dependent on the orientation of the samples. However, for a given orientation, there were only minor variations between the different steels with respect to anisotropy, strength, and ductility. The anisotropy could be correlated with the microstructure through the calculation of Taylor factors based on measurements using electron backscatter diffraction. The minor influence from the initial steel microstructure on the final mechanical properties indicates robustness suitable for mass production. Full article

Exposing insects to mild and/or severe heat can protect them from future heat stress by regulating the expression of certain stress markers. In this study, 60 queen larvae, one day old, were divided into the following two groups: a control group of non-heat-treated mother queens (nH-T MQ) kept for 15 min at 34.5 °C and 70% relative humidity (RH) and a pre-heat-treated mother queen group (pH-T MQ) that was kept for 15 min at 41 °C and 70% RH. Then, 500 daughter workers were collected from brood combs of each group and incubated at room temperature (22 °C) for 30 min, then divided into five groups (n = 100); each group was incubated for one hour at 35, 40, 45, 50, and 55 °C, respectively. The expression levels of several antioxidant genes and markers in 10 workers of each treatment were assessed by relative quantitative Real-Time qPCR and/or ELISA. The pH-T MQ showed improved basal and dynamic expression of several genes and enzymes, which indicated a protective response against heat stress and the effectiveness of tissue hardening on the biological process and/or mechanisms in oxidative stress and antioxidant activity response. These recorded changes may have global implications by improving thermotolerance acquisition during heat stress conditions. Full article

A total of 0.3%C-Cr-Mo-V steel, a high-strength alloy steel widely used in rocket motor housings, suspension systems in high-performance vehicles, etc., is noted due to its high strength-to-weight ratio. However, its high carbon equivalent (CE > 1%) makes it challenging to weld, as it is prone to brittle martensitic formation, which increases the risk of cracking and embrittlement. The present paper focuses on enhancing the microstructure and mechanical properties of 0.3% C-Cr-Mo-V steel by gas tungsten arc welded (GTAW) joints, utilizing post-weld heat treatment and cooling strategies (PWHTCS). A systematic experimental approach was employed to ensure a defect-free weld through dye penetrant testing (DPT) and X-ray radiography techniques. Subsequently, test specimens were extracted from the welded sections and subjected to PWHT protocols, including hardening, tempering, and rapid quenching using air and oil cooling (AC and OC, respectively) mediums. Results show that OC has enhanced tensile strength and hardness while simultaneously maintaining and improving ductility, ensuring a well-balanced combination of strength and toughness. Fractography analysis revealed ductile fracture in AC samples, whereas OC weldments exhibited a mixed ductile–brittle fracture mode. Thus, the findings demonstrate the critical role of PWHTCS, with OC, as an effective method for achieving enhanced mechanical performance and microstructural stability in high-integrity applications. Full article

Stainless steel 17-4PH is valued for its high strength and corrosion resistance but poses machining challenges due to rapid tool wear. This research investigates the use of pulsed electron beam surface treatment to enhance the surface properties of components fabricated by binder jetting additive manufacturing. The aim is to improve the tribological performance compared to the as-sintered condition and the H900 aging process, which optimizes hardness and wear resistance. Printed samples were sintered in a reducing atmosphere and superficially treated with an electron beam by varying the voltage and the pulse count. Results showed that the voltage affects the roughness and thickness of the treated layer, while the number of pulses influences the hardening of the microstructure and, consequently, the wear resistance. A reciprocating linear pin-on-disk wear test was conducted at 2 N and 10 Hz. Surface-treated samples exhibited lower coefficients of friction, though the values approached those of aged samples after the abrasion of the melted layer, indicating a deeper heat-affected zone formation. Still, the friction remained lower than that of as-printed specimens. This study demonstrates that optimizing electron beam parameters is vital for achieving surface performance comparable to bulk aging treatments, with significant implications for long-term wear resistance. Full article

Properties of high early-strength concretes (HESCs) containing Type V, Type III, and rapid hardening calcium sulfoaluminate (CSA) cements were investigated at curing ages of opening time, 24 h, and 28 days. Investigated properties included the fresh (workability, setting time, air content, unit weight, and released heat of hydration), mechanical (compressive and flexural strengths), transport (absorption, volume of permeable voids, water penetration, rapid chloride permeability, and accelerated corrosion resistance), dimensional stability (drying shrinkage), and durability (de-icing salt and abrasion resistance) properties. Test results revealed that the HESC containing Rapid-Set cement achieved the shortest opening time to attain the required minimum strength, followed by Type III and Type V cement HESCs. For the most part, Type V cement HESC produced the best transport and de-icing salt resistance, whereas Rapid-Set cement HESC displayed the best dimensional stability and wear resistance. Full article

Surface layers of agricultural machinery working bodies are subjected to intensive abrasive wear during operation, which leads to rapid wear of equipment and reduction of its service life. To increase the wear resistance of the working surfaces of tools, the method of induction cladding using ‘Sormait-1’ materials is widely used. However, after coating, additional heat treatment is required, which improves physical and mechanical properties of the material and increases its durability. When using electrofriction technology (EFT) hardening, the surface of the parts is subjected to melting under the influence of electric arcs, which affects the surface characteristics of the coatings. In this work, two types of surface treatment of L53 steel were investigated: induction cladding using ‘Sormait-1’ material, as well as a combination of induction cladding and subsequent electrofriction treatment. The coatings were characterized and compared with the substrate in terms of the following parameters: microstructure, phase composition, hardness distribution, and friction-wear characteristics. After induction cladding of the Sormait-1 material, a dendritic structure was formed; however, subsequent electrofriction treatment resulted in a reduction of this dendritic structure, which contributed to an increase in the hardness of the material. The average hardness of the coatings after electrofriction treatment was 786 HV_0.1, which is more than three times the hardness of the substrate. Furthermore, the influence of structural characteristics and hardness on abrasive wear resistance was examined in accordance with ASTM G65 international standards. Field tests were conducted on plough shares before and after electrofriction hardening to evaluate their performance. Each ploughshare was scanned with a structured 3D scanner before and after use in the field. From the scan data, the cutting-edge profile was calculated and three key parameters were determined: linear wear, volumetric wear, and mass reduction. According to the results of field tests, it was found that the service life of the blades hardened by electrofriction technology was 12%–14% higher compared to serial blades processed by induction cladding with the use of ‘Sormait-1’ material. Operational tests of hardened plough shares confirmed the results of laboratory tests and proved the advantages of electrofriction technology for increasing the wear resistance of soil tillage machine working bodies. Full article

The research conducted in this study aimed to determine whether the production of a layered casting in the material system of X46Cr13 steel (working part) and gray cast iron (base part) can be integrated with the hardening process of this steel within the conditions of the casting mold. Accordingly, a series of layered castings was produced by preparing the mold cavity, where a monolithic steel insert was poured with molten gray cast iron with flake graphite. The variable factors in the casting production process included the pouring temperature T_p and the thickness of the support part g. Importantly, given that the hardening of the X46Cr13 steel insert occurred directly within the mold, the selection of casting parameters had to balance the ability to heat the insert to the austenitization temperature Tγ_≥950°C while also creating thermokinetic conditions conducive to the rapid cooling of the system. Therefore, chromite sand—commonly regarded as a rapid-cooling material—was selected as the matrix for the molding material. Based on the conducted studies, it was determined that the thermokinetic properties of this material allowed the surface of the cast working part to be heated to the austenitization temperature. The microstructure consisted of Cr(Fe) carbides within a martensitic-pearlitic matrix, with martensite filling the grains of the primary austenite and pearlite situated along their boundaries. The carbides were primarily located at grain boundaries and, to a lesser extent, within the primary austenite grains. Through transmission electron microscopy and X-ray diffractometry, the type of Cr(Fe) carbide in the microstructure of the working part was identified as M₂₃C₆. Full article

Naphthalene is a fungicide that can also be a phase-change agent owing to its high crystallization enthalpy at about 80 °C. The relatively rapid evaporation of naphthalene as a fungicide and its shape instability after melting are problems solved in this work by its placement into a cured epoxy matrix. The work’s research materials included diglycidyl ether of bisphenol A as an epoxy resin, 4,4′-diaminodiphenyl sulfone as its hardener, and naphthalene as a phase-change agent or a fungicide. Their miscibility was investigated by laser interferometry, the rheological properties of their blends before and during the curing by rotational rheometry, the thermophysical features of the curing process and the resulting phase-change materials by differential scanning calorimetry, and the blends’ morphologies by transmission optical and scanning electron microscopies. Naphthalene and epoxy resin were miscible when heated above 80 °C. This fact allowed obtaining highly concentrated mixtures containing up to 60% naphthalene by high-temperature homogeneous curing with 4,4′-diaminodiphenyl sulfone. The initial solubility of naphthalene was only 19% in uncured epoxy resin but increased strongly upon heating, reducing the viscosity of the reaction mixture, delaying its gelation, and slowing cross-linking. At 20–40% mass fraction of naphthalene, it almost entirely retained its dissolved state after cross-linking as a metastable solution, causing plasticization of the cured epoxy polymer and lowering its glass transition temperature. At 60% naphthalene, about half dissolved within the cured polymer, while the other half formed coarse particles capable of crystallization and thermal energy storage. In summary, the resulting phase-change material stored 42.6 J/g of thermal energy within 62–90 °C and had a glass transition temperature of 46.4 °C at a maximum naphthalene mass fraction of 60% within the epoxy matrix. Full article

In recent years, the issue of increasing the wear resistance of the working bodies of agricultural machinery designed for cutting and breaking the soil has received special attention. The surface layers of working bodies of agricultural machinery during operation are subjected to intensive abrasive wear, which leads to rapid wear of equipment and a reduction in its service life. The induction cladding method using materials such as Sormait-1 is widely used to increase the wear resistance of tool working surfaces. However, after coating, additional heat treatment is required to improve the physical and mechanical properties of the material and increase its durability. In electrofriction technology (EFT) hardening, the surfaces of the parts are subjected to melting under the influence of electric arcs. In this work, three types of surface treatment of L53 steel have been investigated: induction cladding using Sormait-1, electrofriction treatment, and a combination of induction cladding followed by electrofriction treatment. The microstructure was analyzed using optical microscopy and scanning electron microscopy. Erosion and abrasion tests were carried out in accordance with ASTM G65 and ASTM G76-04 international standards to evaluate the wear resistance of the materials under mechanical stress. A dendritic structure was formed after the induction cladding of the Sormait-1 material, but subsequent electrofriction treatment resulted in a reduction of this dendritic structure, which contributed to an increase in the hardness of the material. However, the highest hardness, reaching 965 HV, was recorded after electrofriction treatment of L53 steel. This is explained by needle martensite in the structure, which is formed as a result of quenching. Further, the influence of structural characteristics and hardness on erosion and abrasion wear resistance was examined. The analysis showed that the material microstructure and hardness have a decisive influence on the improvement of wear resistance, especially under conditions of intensive erosion and abrasive friction. Full article

In this study, we investigated the effect of grain size of an initial microstructure (pearlite + ferrite) on a resulting microstructure of induction-hardened microalloyed steel 38MnVS6, which is one topical medium carbon vanadium microalloyed non-quenched and tempered steel used in manufacturing crankshafts for high-power engines. The results show that a coarse initial microstructure could contribute to the incomplete transformation of pearlite + ferrite into austenite in reaustenitization transformation by rapid heating, and the undissolved ferrite remains and locates between the neighboring prior austenite grains after the induction-hardening process. As the coarseness level of the initial microstructure increases from 102 μm to 156 μm, the morphology of undissolved ferrite varies as granule, film, semi-network, and network, in sequence. The undissolved ferrite structures have a thickness of 250–500 nm and appear dark under an optical metallographic view field. To achieve better engineering applications, it is not recommended to eliminate the undissolved ferrite by increasing much heating time for samples with coarser initial microstructures. It is better to achieve a fine original microstructure before the induction-hardening process. For example, microalloying addition of vanadium and titanium plays a role of metallurgical grain refinement via intragranular ferrite nucleation on more sites, and the heating temperature and time of the forging process should be strictly controlled to ensure the existence of fine prior austenite grains before subsequent isothermal phase transformation to pearlite + ferrite. Full article

This study aims to compare the effects of three calcium compounds on the workability, setting time and mechanical properties of red mud (RM)–blast furnace slag (BFS)-based geopolymers. The crystalline phase, hydration process and microstructure of RM-BFS-based geopolymers were characterized by X-ray diffraction (XRD), heat evolution, X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM) tests. The results showed that an appropriate amount of calcium compounds can improve the flowability and compressive strength of the geopolymers, but the excessiveness causes a decrease in strength due to rapid hardening. Other than calcium carbonate, both calcium oxide and calcium chloride played important roles in accelerating the setting times of RM-BFS-based geopolymers. The acceleration in the setting times of geopolymers could be attributed to the calcium hydroxide produced by the dissolution of the calcium compounds, which also provides nucleation sites for the geopolymerization reaction. This study gives new insights into the effect of calcium on the setting times and mechanical properties of geopolymers in the geopolymerization process. Full article

Aluminium nitride (AlN) materials are widely used in heat-dissipation substrates and electronic device packages. However, the application of aluminium nitride ceramics is hindered by the obvious anisotropy and high brittleness of its crystals, leading to poor material surface integrity and high grinding force. With the rapid development of microelectronics, the requirements for the material’s dimensional accuracy, machining efficiency, and surface accuracy are increasing. Therefore, a new machining process is proposed, combining laser and ultrasonic vibration with grinding. The laser–ultrasonic-assisted grinding (LUAG) of aluminium nitride is simulated by molecular dynamics (MD). Meanwhile, the effects of different processing techniques on grinding force, stress distribution, matrix damage mechanism, and subsurface damage depth are systematically investigated and verified by experiments. The results show that laser–ultrasonic-assisted grinding produces 50% lower grinding forces compared to traditional grinding (TG). The microhardness of AlN can reach more than 1200 HV, and the coefficient of friction and wear is reduced by 42.6%. The dislocation lines of the AlN substrate under this process are short but interlaced, making the material prone to phase transformation. Moreover, the subsurface damage depth is low, realising the substrate’s material hardening and wear resistance. These studies not only enhance the comprehension of material build-up and stress damage under the synergistic impact of laser, ultrasonic, and abrasive processing but also indicate that the proposed method can facilitate and realise high-performance machining of aluminium nitride substrate surfaces. Full article

The microstructure and texture of an AlFeMn alloy were studied under different intermediate annealing processes, and the changes in microhardness during cold rolling were analyzed. After annealing at 420 °C with a slow heating rate, the alloy showed a high number of small dispersed particles and recrystallization textures dominated by R texture, with deformation textures of 23.5%. Annealing at 610 °C with a rapid heating rate resulted in a significant decrease in the number of small-sized particles and an increase in recrystallization texture contents, with Cube_ND being the majority. The deformation texture contents decreased to 14.9%. The electrical conductivity of the 420 °C annealed sheet was higher than before annealing, whereas the sheet annealed at 610 °C showed a decrease in electrical conductivity after annealing. This indicated that annealing at 610 °C led to a higher degree of recrystallization and the development of Cube/Cube_ND due to the dissolution of dispersed particles. During the subsequent cold rolling process, the microhardness of both annealed sheets initially increased and then decreased. However, the microhardness of the 420 °C annealed sheet with varying cold rolling reductions consistently remained lower than that of the 610 °C annealed sheet, as was the cold rolling reduction corresponding to the peak microhardness. The results showed that the precipitation at 420 °C facilitated work softening, while the dissolution at 610 °C promoted work hardening. Full article