JOM最新文献

Carbon steel, widely used in nuclear reactor components, is prone to degradation under extreme conditions such as high radiation doses, temperature, and pressure. To increase their longevity, NASA HR-1 alloy was investigated as a protective coating because of its excellent mechanical strength and corrosion resistance. Cold spray deposition was utilized to coat NASA HR-1 onto the substrates, and the effects of process gases, such as nitrogen (N₂) and helium (He), on coating’s microstructure and corrosion behavior were systematically investigated. Microstructural characterization was conducted using optical microscopy, in situ hot-stage transmission electron microscopy, and scanning electron microscopy. NASA HR-1 coatings deposited using He process gas exhibited an average porosity reduction of ~ 95% compared to coatings deposited using N₂ process gas. Electrochemical testing via potentiodynamic polarization in 3.5 wt.% NaCl solution showed He cold-sprayed coatings had ~ 68 times lower corrosion rates than uncoated steel substrates. The 96-h salt fog tests also showed significantly reduced corrosion-induced weight difference in coated specimens, confirming that He cold sprayed coatings reduced material degradation by ~ 83%. Overall, using He as the process gas produced NASA HR-1 coatings with enhanced particle deformation, reduced porosity, and improved corrosion resistance, demonstrating strong potential for extending the structural component life in harsh environments.

With the increasing demand for sustainable resource utilization, the recovery of iron-rich phases from steel slag has garnered significant attention. This study investigated the transformation of iron-bearing phases in synthetic steel slag through thermodynamic analysis. The crystallization behavior of magnesium ferrite spinel (MgFe₂O₄) was explored using in situ high-temperature laser scanning confocal microscopy (HLSCM), phase analysis, and microstructural characterization. The results indicate that an appropriate basicity promotes the transformation of FeO into strongly magnetic MgFe₂O₄, with an optimal basicity of 2.00. Under oxidation conditions, during the cooling process of molten synthetic slag, MgFe₂O₄ crystal nuclei preferentially precipitate at higher temperatures. Subsequently, epitaxial and vertical growth occurs, eventually forming polyhedral structures. As the temperature further decreases to 1350℃, grain migration and aggregation dominate, leading to further growth of MgFe₂O₄ grains. SEM-EDS and XRD analysis further confirmed the transformation of iron-bearing phases into MgFe₂O₄ and its crystallization behavior. This study reveals the key factors influencing the transformation of iron-bearing phases in molten steel slag and the growth control mechanisms of MgFe₂O₄ grains. It provides a theoretical basis for optimizing steel slag oxidation processes to improve iron recovery rates, offering new insights for the resource utilization of industrial solid waste.

The present work deals with two striking 2D materials possessing contrary features and enormous technological perspectives: graphene and h-BN. Graphene attains a tensile strength of 125 GPa and an elasticity modulus of 1.1 TPa. Various methods have been adopted for the synthesis of graphene, including CVD and mechanical exfoliation. It reaches a high thermal conductivity of 5300 W/m K, with a specific surface area of 2630 m²/g. With its high carrier mobility of 2 × 10⁵ cm²/V s, it enables advanced nanoelectronics and energy storage. Hexagonal boron nitride is an insulating member with a band gap of ~ 5.5 eV. It has a very high thermal conductivity of 600–1000 W/m K and is stable up to 2000°C in inert conditions, synthesized by the CVD method, retains excellent structural integrity, and presents high dielectric strength in the range of 30–40 kV/mm, which renders it an ideal material for applications such as electronic insulation at high temperatures. This review underlines the potential synergy of graphene and h-BN for future applications in nanotechnology, semiconductors, and biomedicine.

Cu-graphite composites (CGC) are used in various applications, such as heat dissipation, lubrication, and electrical contact materials. However, the weak interface bonding between graphite and Cu significantly limits the performance of these composites. To improve the interface bonding and explore new approaches, this study employs an in situ fabrication method to prepare a Ti₂SnC-modified layer on the surface of graphite particles, followed by coating Cu onto the Ti₂SnC-modified layer. Further, the Cu-coated Ti₂SnC-modified graphite powder was used as the raw material for composite preparation via vacuum hot-press sintering. The results show that the Ti₂SnC-modified layer on the graphite surface and Cu can undergo mutual diffusion during sintering, forming a metallurgical bond. Ultimately, the Ti₂SnC-modified layer facilitates the bonding between graphite and Cu, which is chemical-metallurgical.

High-temperature heat treatment can cause carbon loss in steel due to reactions with oxygen, reducing strength and durability. High-temperature protective coatings offer a cost-effective solution to minimize decarburization and its effects. In this study, seven commercially available high-temperature coatings (WBC, ASC, AS, ASV, HTG, HTR-Zr, and HTR-Si) were applied to AISI 4340 low-alloy steel via spraying or dipping at room temperature, and their decarburization protection was evaluated at 1000°C, 1100°C, and 1200°C for 30, 60, 90, and 120 min under atmospheric conditions. The results were also compared with those obtained by wrapping stainless-steel foils on AISI 4340 low-alloy steel substrates. Optical microscopy and micro-indentation hardness measurements were used to determine the decarburization depth/maximum affected depth and to investigate the formation of free ferrite depth and partial decarburization depth during heat treatment, while profilometry was conducted to study surface irregularities after heat treatment. The samples were subsequently characterized using scanning electron microscopy/energy dispersive spectroscopy to examine surface morphology and elemental composition. WBC showed the best decarburization protection by reducing the decarburization depth by 21% to 44%, followed by zirconia oxide-based (HTR-Zr) coating, which reduced the depth of decarburization by 20% to 37%. This was attributed to the formation of thicker and more consistent Al₂O₃ and SiO₂ protective layers. Additionally, decarburization modeling was also performed using Fick’s second law to observe the variation between experimental and modeled depth values, where the same hardness values are observed. Good agreement was observed between experimental and theoretical depth values. These findings can be applied to other steels with similar compositions.