Martensitic phase transformation plays a crucial role in the functional properties of shape memory metals and alloys, profoundly affecting the mechanical behavior, including transformation-induced plasticity effect in metallic materials, especially steels. Considering the wide-ranging applications and the absolute usage volume, iron (or steels) is undoubtedly the metal among functional and structural materials that is used the most in the world. Quenching has long been employed as a straightforward and historically recognized method for hardening carbon steels, yet its underlying scientific mechanisms remain incompletely understood. Recent transmission electron microscopy investigations have revealed that quenched Fe–C martensite consists of ultrafine ferrite and carbide grains, typically measuring about ∼1-2 nm in size. Rapid quenching can prevent the coarsening of the ultrafine grains. These ultrafine two-phase grains ― ferrite (α-Fe) and carbide (ω-Fe3C) ― are responsible for quenching induced hardening and forming twinned martensite with the ω-Fe3C located at the α-Fe twinning-boundaries. Tempering (auto/post) results in coarsening or recrystallization of fine crystals, leading to the formation of various microstructure, such as pearlite, bainite and tempered martensite. The present study seeks to elucidate the atomic scale mechanisms of quenching and hardening in carbon steels, with particular emphasis on the behavior of carbon atoms during the formation of diverse microstructures. Carbon atoms cannot be super-saturated in the α-Fe lattice, instead, carbides can only precipitate from austenite. The ultrafine grains resulting from martensitic transformation are the origin of quenching hardening. These ultrafine grains consist of both α-Fe and carbides (including θ-Fe3C cementite and its precursors).

Recently, a new phase, ω–Fe, has been observed in martensitic substructures, providing a new path for studying the position and evolution of nitrogen in high-nitrogen steels. In this paper, the density functional method was used to investigate the thermodynamic and dynamic stability of N atoms in the phases of ω–Fe, α–Fe, and γ–Fe in martensite, as well as the influence of magnetic order on them. The calculated results show that in the pure Fe phases, ferromagnetic α–Fe is a stable phase both in thermodynamics and dynamics. ω–Fe and γ–Fe are most stable in ferrimagnetism and show dynamic stability, while in ferromagnetic state they are unstable in both thermodynamics and dynamics. N-atom doping of 25% (Fe3N) makes γ–Fe and ω–Fe thermodynamically and dynamically stable in ferromagnetic state. However, a higher N content is not conducive to the stability of ω–Fe and γ–Fe. The electronic structure shows that as the content of N atoms becomes higher than 25%, the 2p orbitals of N atoms move towards the Fermi level and become more dispersed, resulting in a large contribution of the density of states at the Fermi level. In addition, N atoms are not conducive to the stability of α–Fe, as they relax to the structure of γ–Fe at 25% N content (Fe3N), while α–Fe in higher N contents (Fe3N2 and FeN) relaxes to the structure of ω–Fe correspondingly. Obviously, N tends to stabilize in the ω and γ phases in martensite, and our study provides a new clue for the formation mechanism of nitrides and martensitic transformation in Fe–N alloys.

Photoelectrochemical (PEC) water splitting is a promising green technology for converting solar energy into chemical energy, with great potential for clean energy production. However, developing stable photoanodes remains a significant challenge for large-scale application. Tungsten trioxide (WO3) is a promising semiconductor due to its suitable bandgap, efficient charge separation, environmental friendliness, and low cost. However, WO3 is unstable, mainly due to photocorrosion, chemical corrosion, and peroxide accumulation. This review provides a comprehensive summary of various modification strategies for WO3-based photoanodes, including fundamental modification, doping-induced modification, multilayer structure modification, and external factors modulation. The focus is on assessing the impact of these modification strategies on material stability and evaluating their overall effectiveness. This review aims to provide valuable insights into the design and fabrication of highly stable WO3 semiconductor materials and explores the future prospects and challenges of their application in PEC water splitting.

Eco-friendly water-based epoxy resins (WEP) coatings are widely applied for surface corrosion protection in marine engineering structures but their anti-corrosion performance needs to be further improved. A novel multifunctional benzotriazole (BTA)-loaded PANI@SiO 2 @h-BN (PSB) composite filler was developed to enhance the anti-corrosion and self-repairing capabilities of WEP coatings. Through sol-gel modification and in-situ polymerization, SiO 2 decoration facilitated the uniform dispersion of two-dimensional hexagonal boron nitride (h-BN) in WEP matrices, while polyaniline (PANI) provided active passivation protection. The synergistic effects of PANI and releasing of BTA inhibitors enable corrosion rates orders of magnitudes lower than pure WEP coating. Electrochemical characterization demonstrated exceptional barrier properties (|Z| at 0.01 Hz > 10 9 Ω cm 2 after 30 days immersion in 3.5 wt% NaCl) and self-repairing functionality through chelate/passivation layer formation. The composite coating exhibited enhanced hydrophobicity, mechanical durability, providing a sustainable solution for marine infrastructure protection.

Hydrogen has garnered considerable attention as a promising energy source for addressing contemporary environmental degradation and energy scarcity challenges. Electrocatalytic water splitting for hydrogen production has emerged as an environmentally friendly and versatile method, offering high purity. However, the development of cost-effective electrocatalytic catalysts using abundant and inexpensive materials is crucial. In this study, we successfully synthesized nitrogen-doped Co6Mo6C supported on nitrogen-doped graphene (N-Co6Mo6C/NC). The catalyst exhibited high performance and durability in alkaline electrolytes (1.0 M KOH) for hydrogen evolution, showcasing an overpotential of 185 mV at a current density of 100 mA cm−2 and a Tafel slope of 80 mV dec−1. These findings present a novel avenue for the fabrication of efficient bimetallic carbide catalysts.

A universal machine learning framework is proposed to predict and classify membrane performance efficiently and accurately, achieved by combining classical density functional theory and string method. Through application of this framework, we conducted high-throughput computations under industrial conditions, utilizing an extensive database containing nearly 70,000 covalent organic framework (COF) structures for CH4/H-2 separation. The best-performing COF identified surpasses the materials reported in the previously documented MOF and COF databases, exhibiting an impressive adsorption selectivity for CH4/H-2 exceeding 82 and a membrane selectivity reaching as high as 248. More impressively, some of the best candidates identified from this framework have been verified through previous experimental works. Furthermore, the automated machine learning framework and its corresponding scoring system not only enable rapid identification of promising membrane materials from a vast material space but also contribute to a comprehensive understanding of the governing mechanisms that determine separation performance.

The influence of hydrogen charging potentials on the hydrogen embrittlement susceptibility of R6 ultra-high strength mooring chain steel was investigated via constant potential hydrogen charging slow strain rate tensile tests combined with thermal desorption analysis. The results reveal that hydrogen charging leads to a 38.94% decrease in elongation, while the impact on tensile strength is relatively minor. Furthermore, the specimens experienced intergranular cracking at the critical potential of −1150 mV, with the size of the brittle region increasing as the negative charging potential becomes more negative. And, hydrogen atoms can cause local embrittlement of materials and increase KAM value.

The fracture behaviours of pearlite structures in several typical carbon steels were investigated by scanning electron microscopy (SEM). Microstructural analysis indicated that the fracture of pearlite is a mixed ductile-brittle fracture, and brittle fracture has cleavage fracture characteristics, which often occur inside the pearlite structure. The fracture surface can exhibit any orientation relationship with the ferrite/cementite interface plane in the pearlite structure. The two phases in the pearlite structure (ferrite (α-Fe) and cementite (θ-Fe3C)) are fine grains rather than single-crystal platelets. The cleavage fracture mechanism in any direction of pearlite structure occurs due to the fine grain substructure.

Developing non-noble-metal electrocatalysts for hydrogen evolution reactions with high activity and stability is the key issue in green hydrogen generation based on electrolytic water splitting. It has been recognized that the stacking of large CoP particles limits the intrinsic activity of as-synthesized CoP catalyst for hydrogen evolution reaction. In the present study, N-MoxC/CoP-0.5 with excellent electrocatalytic activity for hydrogen evolution reaction was prepared using N-MoxC as decoration. A reasonable overpotential of 106 mV (at 10 mA cm(-2)) and a Tafel slope of 59 mV dec(-1) in 1.0 M KOH solution was achieved with N-MoxC/CoP-0.5 electrocatalyst, which exhibits superior activity even after working for 37 h. Uniformly distributed ultrafine nanoclusters of the N-MoxC/CoP-0.5 hybrids could provide sufficient interfaces for enhanced charge transfer. The effective capacity of the hydrogen evolution reaction could be preserved in the complex, and the enlarged electrocatalytic surface area could be expected to offer more active sites for the reaction.

After a brief review of the history of pearlite structures in carbon steels, particularly on the pearlite formation mechanism, recent experimental investigations on the pearlite substructure are presented to express a distinct point of view. The water-quenched high-carbon pearlite substructure is investigated in detail by means of scanning electron microscopy and transmission electron microscopy. In the experimental observation results, it is shown that the cementite layer or ferrite layer in pearlite is composed of fine grains, which cannot be simply explained by traditional nucleation and grain growth mechanisms. However, the fine grain structure can be explained by the martensitic transformation products (twinned martensite with ultrafine grains of alpha-Fe and twinning boundaries omega-Fe (or omega-Fe3C)) and detwinning process. Upon tempering or detwinning, recrystallization of the ultrafine grains of both crystalline phases occurs to form the initial pearlite structure, while the grain size of both phases is still fine. The twinned martensite can be treated as the precursor of pearlite structure (pearlite nucleation stage), and the detwinning process can be regarded as the growth of the pearlite structure. Thus, the pearlite reaction can be described as follows: austenite -> twinned martensite -> pearlite. Scanning electron microscopy images of the pearlite structure in the boiling-water-quenched Fe-1.4C (wt%) alloy: a) low-magnification image and b) high-magnification image. The bright "layers" (cementite layers) are formed by the alignment of fine cementite particles, which have a uniform size distribution and almost the same orientation. Each bright-contrast dot in the high-magnification image corresponds to one cementite particle.image (c) 2024 WILEY-VCH GmbH

A new metal-matrix composite, fine Ti(C, N) particles reinforced CoCrFeNiTi high-entropy alloy (HEA), were successfully fabricated via mechanical alloying and spark plasma sintering process. Graphite carbon nitrides (g-C3N4) particles and equiatomic CoCrFeNiTi HEA powders were used as the original materials. The microstructural investigations have been carried out with scanning electron microscope (SEM) and high-resolution transmission electron microscope (HRTEM), and the results reveal that the increase in strength can be ascribed to grain refinement and dislocation strengthening, particularly the fine Ti(C, N) particle strengthening. The fracture modes of composites are mainly combination of brittle fracture with ductile fracture. An interesting microstructural feature is that the fine HEA grains are distributed within Ti(C, N) particles forming a core-shell structure, which further improves the fracture toughness of the composites. The final composite (Ti(C, N)/CoCrFeNiTi HEA) shows exhibits the best combination of compressive strength and fracture toughness, which are 2965 MP and 12.4 MPa m1/2, respectively. The present study not only expands the application field of g-C3N4 but also provides a new idea for the preparation of composites reinforced with Ti(C, N) particles.

A silica/aminated kaolin (SiO2@AK) composite was prepared by modifying kaolin and loading silica, using intercalation complex method and sol-gel method. Quantitative composites were dispersed in epoxy resin to obtain a silica/aminated kaolin/epoxy resin composite coating (SiO2@AK/EP) on stainless steel. The results showed that the thickness of the dry coating was approximately 110 +/- 10 mu m, and the surface was flat without evident agglomeration. As the SiO2@AK composite was introduced, the water contact angle increased from 40 degrees to 88 degrees, the average surface roughness of the prepared composite coating was reduced from 10.3 nm to 3.19 nm, and the corrosion current decreased by nearly three orders of magnitude. After the coating was soaked in 3.5 wt% NaCl solution for 30 days, the impedance modulus of the composite coating remained above 2.511 x 10(9) Omega cm(2), reflecting that the introduction of the composite could effectively improve the anticorrosion property of the epoxy resin.

Capparis spinosa L. (CSL) is used in traditional medicinal purposes for wound dressing because it contains natural phenolic and flavonoid active compounds. In the current study, a bilayer of biocompatible and mechanically stable nanofiber scaffolds with polycaprolactone (PCL)/zinc oxide and Capparis spinosa L. ethyl acetate extract (CSLE)/polylactic acid (PLA) layers was successfully prepared by an electrostatic spinning technique. Microstructural observations carried out by scanning electron microscopy (SEM) have shown that the nanofibers with a smooth surface are continuous and bead-free, and that the size distribution is uniform, with an average diameter of 314.15 nm. The results of careful observation further suggested that polymers in the nanofibers have excellent compatibility with drugs. The results of Fourier transform infrared (FTIR) spectroscopy suggested that CSLE and zinc oxide nanoparticles (ZnO) were successfully loaded in the nanofiber membranes. Water contact angle measurements revealed that the bilayer nanofiber membranes exhibited satisfactory wettability (outside layer, 130°; inner layer, 72.4°). Tensile testing showed that the bilayer PCL/ZnO-CSLE/PLA nanofibers remained unbroken until reaching 10.69 MPa, which is much higher than the tensile strengths of the individual layers or the individual components. Moreover, agar disk diffusion assessment confirmed that the bilayer nanofiber membranes obviously hindered bacterial growth. Cytotoxicity studies showed that the bilayer nanofiber membranes effectively accelerated cell proliferation. The investigated PCL/ZnO-CSLE/PLA bilayer nanofibers have potential for use as membranes for wound dressing applications.

Two mining chain steels 23MnNiMoCr5-4 and 0.3C0.2Si0.3Mn4.2(Cr + Ni + Mo) with tensile strengths of 1200 MPa and 1250 MPa, respectively, were employed to investigate their hydrogen embrittlement behaviors by slow strain rate tests combined with thermal desorption analyses. It is shown that at initial stage the fracture stress decreases linearly as the hydrogen content increases, and the turning points occur at hydrogen content of 1.2 wppm for 0.3C0.2Si0.3Mn4.2(Cr + Ni + Mo) and 0.26 wppm for 23MnNiMoCr5-4. The fractured surface observation suggests that the ratio of intergranular fracture area to quasi-cleavage area increases dramatically at the turning points. The maximum hydrogen contents resulting from the corrosive HCl solutions with pHs of 2 are approximately 0.6 wppm 0.3C0.2Si0.3Mn4.2(Cr + Ni + Mo) and 0.11 wppm for 23MnNiMoCr5-4, corresponding to the activation energies for hydrogen desorption are 21.57 kJ/mol and 14.53 kJ/mol, respectively.

The key issue for green hydrogen generation in the next decades will be the development of non-noble-metal electrocatalysts for hydrogen evolution revolution (HER) from water splitting with high activity and stability. Herein, the as-synthesized CoP with its effective charge transfer capability was utilized, and N-MoxC was then further modified on it. The best electrocatalytic HER activity of N-MoxC/CoP-0.5 was achieved with a reasonable overpotential of 106 mV (at 10 mA cm-2) and a Tafel slope of 59 mV dec-1 in 1.0 M KOH solution. It continued to have superior activity after working continuously for 37 h. N-MoxC modification of CoP results in uniformly distributed nanoparticles with enlarged specific surface area. The formation of the N-MoxC/CoP-m complex preserved CoP's efficient charge transfer rate, while the improved electrocatalytic surface area was predicted to offer more active sites for HER. The synergistic cooperation of the complex’s constituents resulted in enhanced HER activity and good stability.

Modified montmorillonite/graphene oxide composites (AM@GO) were prepared by a hydrothermal method with silane coupling agent-modified montmorillonite (APTES@MMT) and combined with GO. The structures of the composites were characterized by FTIR, XRD, Raman spectroscopy, BET analysis, and SEM. The results showed that the composites had increased interlayer spacing and formed a loosely laminated stacked structure. The specific surface area (31.6863 m 2 /g) and pore volume (0.0104 cm 3 /g) of the composites increased. The hydrophobic and anticorrosive properties of the composite coatings were investigated and compared to the epoxy coating. The composite coatings (AM@GO/EP) had larger contact angles and smoother surfaces than the epoxy coating (EP). After 30 days of immersion, the value of |Z| 0.01 Hz was approximately 10 11 Ω cm 2 , which had changed slightly since initial immersion. Mechanistic analysis shows that the improved corrosion resistance of the composite coatings was due to the high specific surface area of the 2D material, the oxygen-containing groups of GO, the amino groups of APTES@MMT and the synergy between the MMT and the GO nanosheets.

与其他金属或合金相比,钢铁材料的应用更为广泛.淬火和回火的钢的高强度、高硬度和韧性主要源于其马氏体组织.虽然对钢中马氏体组织的研究已逾百年,可是与马氏体相变有关的某些关键科学问题却依然不清楚.值此X射线衍射应用于钢铁材料马氏体组织研究百年之际,简要回顾和探讨了碳钢马氏体的几个基本科学问题.

In quenched Fe-C (C: 0.0 similar to 2.0 wt.%) binary alloys, the body-centered cubic (BCC) {112}< 111 > type twin structure (density, size and morphology) in martensite was investigated by means of transmission electron microscopy (TEM). In the samples quenched to room temperature, the twin density increased as the carbon content increased. In the carbon free or pure iron sample, no twin structure was observed. In high carbon martensite, a high density of twins could be seen with twin thickness of 1 nm-2 nm, which is of the scale of the smallest alpha-Fe grain. The twin density variance is discussed based on a detwinning process, which occurs upon cooling. The twin, as an initial product of martensitic transformation, would experience a higher temperature auto-tempering process in low carbon alloys than in high carbon samples. A noticeable detwinning process takes place in low carbon alloys and results in a low density of twins observed at room temperature. Martensite starting (M-s) temperature plays a crucial role in the detwinning or auto tempering effect on the twins. (C)2022 The Author(s). Published by Elsevier B.V.

The substructure in pearlite structure was investigated in depth by means of transmission electron microscope（TEM） and scanning electron microscope（SEM）. The results show that the pearlite in carbin steel has a own evolution process. Unlike the traditional nucleation and grain growth via the free diffusion of carbon atoms, the laminar pearlite can be formed via the transformation of twinned martensite during low-temperature tempering. Due to the presence of twinning boundary phase in the as-quenched twinned martensite, the twinned martensite（α-Fe/ω-Fe 3 C/α-Fe） exhibits as characteristic as fine laminar pearlite. From observation by transmission electron microscope it is showed that both α-Fe and ω-Fe 3 C phases in the as-quenched martensite are ultra-fine, and recrystallize and coarsen during the tempering, as well as the ω-Fe 3 C phase transforms into θ-Fe 3 C, and the twinning relationship disappears, thus resulting in the formation of a stable pearlite structure.

Understanding the ultrafine substructure in freshly formed Fe-C martensite is the key point to reveal the real martensitic transformation mechanism. As-quenched martensite, whose transformation temperature is close to room temperature, has been investigated in detail by means of transmission electron microscopy (TEM) in this study. The observation results revealed that the freshly formed martensite after quenching is actually composed of ultrafine crystallites with a grain size of 1–2 nm. The present observation result matches well with the suggestion based on X-ray studies carried out one hundred years ago. Such nanocrystals are distributed throughout the entire martensite. The whole martensite shows a uniform contrast under both bright and dark field observation modes, irrespective of what observation directions are chosen. No defect contrast can be observed inside each nanocrystal. However, a body-centered cubic {112}<111>-type twinning relationship exists among the ultrafine α-Fe grains. Such ultrafine α-Fe grains or crystallites are the root cause of the fine microstructure formed in martensitic steels and high hardness after martensitic transformation. The formation mechanism of the ultrafine α-Fe grains in the freshly formed martensite will be discussed based on a new γ → α phase transformation mechanism.