Search Results (373)

The structure, mechanical and electrical properties of Zr-based melt-spun Zr–(Al)–Ni–Cr–Ag alloys were investigated as a function of elemental composition. X-ray diffraction reveals the structural evolution from fully amorphous to nanocrystalline states, with the latter containing Zr₂Ni “big-cube” (space group Fd3̄m, cF96), fcc-Zr₂Ni, and β-Zr phases depending on the alloying ratio: Cr-rich compositions (≥15 at.%) stabilize β-Zr within the amorphous matrix, whereas Ag-enriched alloys promote “big-cube” phase formation. Ag atoms can replace both Zr and Ni sites in the “big-cube” lattice, yielding a (Zr,Ag)₂(Ni,Ag) solid solution and highlighting its role as a structural bridge between the amorphous and crystalline states. Nanoindentation measurements show that hardness increases from 6.5 GPa in fully amorphous ribbons to 10.12 GPa in three-phase nanocrystalline composites, with an H/E ratio of ~0.08 indicating predominantly covalent bonding, and the fracture strength of the amorphous alloys is ~2 GPa, exceeding literature values for related Zr-based systems. Electrical resistivity measurements over the 4–298 K range show that most alloys deviate from Matthiessen’s rule, exhibiting a negative temperature coefficient of resistivity consistent with the Mooij correlation; the presence of the icosahedrally ordered “big-cube” phase further increases resistivity relative to fully amorphous alloys. Full article

Cementite morphology is known to govern the mechanical performance of steels, yet its influence on actual crystal structure, like unit cell parameters, is not well quantified. Here, we show that cementite morphology-dependent surface stresses generate measurable lattice distortion in nanocrystalline cementite. Lamellar and spheroidized cementite powders were extracted from a Cr-alloyed hypereutectoid steel and characterized by high-energy synchrotron X-ray diffraction combined with double-Voigt profile modeling. Despite a higher Cr content in spheroidized cementite, lamellar cementite exhibits systematically larger lattice parameters, corresponding to an average volumetric lattice strain of 6.3 ± 2.2 × 10⁻⁴. This counter-intuitive expansion is rationalized by a continuum mechanics framework that incorporates the orthorhombic elastic anisotropy of cementite and particle morphology. The model predicts the sign and magnitude of morphology-induced lattice strain, demonstrating that surface-stress effects constitute a systematic bias in diffraction-derived lattice parameters of nanostructured carbides. Full article

This study investigates the microstructural evolution, mechanical performance, and electrochemical corrosion behavior of nanocrystalline boride layers formed on an Fe-20Cr-5Al ferritic alloy by pack boriding at 950 °C for 4 h. X-ray diffraction (XRD) and scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) analyses confirmed the formation of a hierarchical boride layer approximately 80–85 μm in thickness, consisting of orthorhombic (Fe,Cr)B and tetragonal (Fe,Cr)₂B phases at the surface and (Fe,Cr)₂₃(C,B)₆ carboboride phases in the diffusion zone, the latter attributed to the carbon push-ahead mechanism. Rietveld refinement yielded a quantitative phase fraction of 51.9 wt.%. (Fe,Cr)B, 46.1 wt.% Fe₂B, and 2.0 wt.% (Fe,Cr)₂₃(C,B)₆, with a theoretical boride layer density of 7.40 g cm⁻³. Williamson–Hall analysis yielded an average crystallite size of 50.7 nm and a microstrain of 1.686 × 10⁻³, confirming the nanocrystalline character of the boride phases. Mechanical evaluation revealed a ~9-fold increase in surface hardness in Fe20Cr5Al-B relative to Fe20Cr5Al, reaching 1854 HV (18.18 GPa). Tribological testing demonstrated an ~18-fold reduction in wear rate (from 3.29 × 10⁻⁴ to 1.82 × 10⁻⁵ mm³/m) and a 14.5% reduction in the coefficient of friction (0.76→0.65), confirming the effectiveness of the boride layer as a tribological barrier. However, electrochemical analyses in 5 wt.% H₂SO₄ revealed a paradoxical deterioration in corrosion resistance: despite a noble shift in E_corr from −0.459 to −0.295 V, the corrosion rate increased ~4-fold (from 9.67 × 10⁻³ to 3.83 × 10⁻² mm/year), driven by Al-repulsion-induced passive film loss and micro-galvanic cell formation through micro-crack and porosity networks. These findings emphasize that while pack-boriding is highly effective for tribological enhancement of FeCrAl alloys, minimizing boride layer defects is essential to achieve concurrent corrosion protection in acidic environments. Full article

A nanostructured Ti_0.8V_0.2C solid solution carbide was successfully synthesized via high-energy mechanical alloying (MA) of elemental Ti, V, and C powders for 20 h in a planetary ball mill under argon atmosphere. Phase evolution and microstructural transformation were tracked using XRD, SEM/EDX, and TEM. Progressive alloying resulted in continuous refinement of the carbide structure, where the crystallite size was reduced to ~11–15 nm and the lattice microstrain increased up to 0.93 % after 20 h of MA. TEM observations confirmed the formation of highly dispersed nanocrystalline Ti_0.8V_0.2C solid-solution carbide particles with sizes of 15–20 nm. This work demonstrates the effectiveness of MA in generating a novel Ti–V-based nanocarbide solid solution and highlights the critical role of milling duration in tailoring structural refinement and defect accumulation at the nanoscale. Full article

CoCrNiTiAl_x high-entropy alloy films with varied Al contents were fabricated on 42CrMo steel substrates via magnetron sputtering. By adjusting the sputtering power of the Al target, an investigation was systematically carried out to explore the effect of different Al contents on the microstructural evolution, mechanical properties, and corrosion resistance of the film, with the underlying synergistic mechanism governing these properties being elucidated. With increasing Al content, the film microstructure gradually transforms from an amorphous phase at low Al contents to a nanocrystalline–amorphous composite structure, until it is converted into the BCC phase, and the film’s crystallinity exhibits a trend of first increasing and then decreasing. In terms of mechanical properties, the film hardness is significantly enhanced from 7.6 ± 1.3 GPa to 18.9 ± 1.1 GPa with increasing Al content, while the toughness gradually declines. Wear tests show that the film wear rate first decreases and then increases with rising Al content, reaching a minimum of 2.06 × 10⁻⁵ mm³/N·m. The superior protective state, characterized by a corrosion potential reaching −361.2 mV and corrosion current density dropping to 1.12 μA/cm², arises from the generation of an integrated, consistently structured composite passivation barrier in 3.5 wt.% solution. This study confirms that appropriate Al doping can synergistically optimize the microstructure, mechanical properties, and corrosion resistance of CoCrNiTiAl_x films, providing experimental and theoretical support for the compositional design and engineering applications of high-performance high-entropy alloy protective films. Full article

High-temperature corrosion severely impairs the service life of boiler heating tubes and threatens the safe and economical operation of thermal power units. With diversified fuels (coal, biomass and refuse-derived fuels) and continuously elevated operating parameters (steam temperature exceeding 620 °C for ultra-supercritical units), boiler heating surfaces are exposed to increasingly complex corrosive environments. High-temperature oxidation, sulfidation, chlorination, molten salt hot corrosion and deposit-induced multi-factor coupled corrosion coexist and exacerbate each other. This paper adopts a four-dimensional analytical framework of “mechanisms–technologies–materials–evaluation” to systematically summarize relevant research progress. From the perspective of corrosion mechanisms, the evolution of understandings from single high-temperature oxidation to multi-factor coupled corrosion is reviewed. In terms of surface coating technologies, seven mainstream processes including HVOF/HVAF spraying, plasma spraying, cold spraying, laser cladding and weld overlay are compared in terms of preparation characteristics and engineering applicability. For coating materials, twelve material systems such as NiCr alloys, MCrAlY, cermets, Fe-based amorphous/nanocrystalline alloys and high-entropy alloys are evaluated for their corrosion resistance under diverse service conditions. As for monitoring and evaluation, this work introduces full-range corrosion management technologies covering electrochemical monitoring, non-destructive testing, numerical simulation and life assessment. Finally, the paper discusses the application prospects of gradient coating design, AI-assisted material screening and digital twin technology, and points out key research gaps including long-term service reliability verification of coatings and quantitative prediction models for multi-factor coupled corrosion. Full article

The coupled effects of Ni and Ti additions on amorphization, spark plasma sintering (SPS) response, and hardness evolution were investigated in Al-rich Al–Fe–Nb-based metastable alloys. Mechanically alloyed Al₈₂Fe₁₄Nb₂Ni₂, Al₈₂Fe₁₄Nb₂Ti₂, and Al₈₂Fe₁₂Nb₂Ni₂Ti₂ powders showed progressive loss of long-range order, with the quinary alloy exhibiting the strongest amorphization tendency, consistent with its higher configurational entropy (5.420 J·mol⁻¹·K⁻¹) and more negative mixing enthalpy (−9.36 kJ·mol⁻¹). SPS displacement analysis revealed that primary displacement contribution occurs during heating and is progressively limited by crystallization-induced stiffening. Consolidation at 500 °C produced amorphous–nanocrystalline composites containing Al₁₃Fe₄ and Al₃Nb, whereas increasing the temperature to 550 °C promoted further devitrification. The highest hardness, 445.4 HV, was obtained for Al₈₂Fe₁₄Nb₂Ni₂, despite its lower amorphous-forming ability than the quinary alloy. This demonstrates that hardness is controlled not by maximum amorphization, but by the kinetic balance between amorphous retention, fine intermetallic precipitation, and densification efficiency. The results identify SPS as a coupled densification–transformation route for designing high-strength Al-based amorphous–nanocrystalline alloys. Full article

High-entropy alloys exhibit a broad light-responsive spectrum, spanning the ultraviolet to visible range, and their light absorption coefficient is significantly higher than that of traditional binary oxides. Cr/AlCrNbSiTiN/AlCrNbSiTiO gradient nano-multilayer coatings with excellent solar selective absorption properties are prepared using ion source enhanced magnetron sputtering. The effects of thickness of the absorption layer of AlCrNbSiTiN (3/4/5 min, denoted as S-3/4/5) are systematically investigated. It is worth noting that nano-multilayer coatings of S-3, S-4, and S-5 exhibit nearly perfect absorption rates of 0.9847, 0.9888, and 0.9879, respectively. The TEM images shows clear interfaces between the various coating layers, exhibiting a gradient structure that combines nanocrystalline and amorphous characteristics. From the substrate to the surface, there is an increase in the content of nanocrystalline phases, coarsening of grain sizes, and a decrease in the amount of amorphous phases. The primary absorption layer of AlCrNbSiTiN displays a typical face-centered cubic nitride structure. The XPS analysis reveals that the high-valent oxides (Nb⁵⁺, Cr⁶⁺) ensure thermal stability, whereas mixed valence states of Cr³⁺/Cr⁶⁺ may enhance visible light absorption through multi-electron transitions. This study analyzes how both the thickness of absorbing layers and high-temperature annealing affect the optical properties and photothermal conversion performance of AlCrNbSiTiN-based high-entropy coatings, which provides valuable insights for developing high-performance selective absorbers. Full article

Metallic glasses can be transformed into nanocrystalline–amorphous alloys via controlled crystallisation with fast nucleation and slow grain growth. This can be achieved either through appropriate chemical composition of amorphous precursors or by applying ultra-rapid annealing (URA). Typically, heating between preheated copper blocks is used to ensure the URA conditions. In this work, ribbons were heated by an electric current flowing along their length, and the temperature was monitored using pyrometers. The investigated alloys were Fe_86-xNi_xB₁₄ (at. %), where x = 4, 6 or 10. Properly adjusted isothermal annealing at 380–410 °C for 1–20 s induced crystallisation, with the nanocrystalline bcc-Fe(Ni) phase occupying 0–55% of the volume. With increasing annealing time, the coercive field increased from 9 A/m in the amorphous state to 25 A/m and 17 A/m for x = 4 and x = 10, respectively. Transmission electron microscopy confirmed that samples annealed at higher temperatures for shorter times exhibited smaller grain sizes compared to those annealed at lower temperatures for longer times, which resulted in improved magnetic softness. An increase in nickel content reduced coercivity, improved ductility, and offered a wider window for the choice of annealing temperature. Full article

We constructed a multi-layer composite magnetic shield composed of Fe-based nanocrystalline (FN) and Co-based amorphous (CA) ribbons, and focused on the influence of the number of layers and their arrangement on the shielding effectiveness (SE). Finite element analysis (FEA) and layer-by-layer inversion calculations were performed to analyze the attenuation process of the magnetic field between shield layers. Increasing the number of shield layers improves the maximum value of SE (SE_max) and significantly broadens the working range (WWR). In a weak magnetic field, CA exhibits higher shielding performance, whereas FN is better in a strong magnetic field. The FN/FN/CA combination (FN is closer to the field source) exhibits an SE_max of up to 51.7 dB within a WWR of 674.3 A/m, and demonstrates a 14.4% improvement in SE compared to FN/FN/FN combination across the entire tested magnetic field range. Finally, a gradient layering design is proposed that enables each layer to operate within its optimal permeability range, thereby improving the overall SE and broadening the effective working magnetic field range. Full article

Molecular dynamics (MD) simulations were performed to investigate the dynamic deposition behavior, growth mechanism, and mechanical properties of nickel–tungsten (Ni-W) alloy films on single-crystal Al(001) substrates. The results demonstrate that the incorporation of W atoms lowers the Ehrlich–Schwoebel (ES) barrier for Ni adatoms, facilitating downhill diffusion and effectively suppressing Volmer–Weber (VW) mode, thereby improving surface morphology and reducing film roughness. Additionally, W atoms exhibit a tendency to segregate at grain boundaries, inducing lattice distortion and structural disorder. With increasing W content (≥15 at%), the films undergo a transition from a nanocrystalline to an amorphous structure. Nanoindentation simulations reveal that film hardness increases with W content, with the strengthening mechanism being composition-dependent: dislocation pinning dominates at low W concentrations (≤5 at%), while the formation of an amorphous structure emerges as the primary strengthening mechanism at higher W contents (≥15 at%). This work elucidates the growth regulation and strengthening mechanisms of Ni-W films from an atomic-scale perspective, providing a theoretical foundation and simulation-driven guidance for the design and optimization of high-performance, environmentally benign Ni-W coatings. Full article

A 2D multiphase-flow coupling simulation model for preparing nanocrystalline ribbons using planar-flow casting (PFC) with a cooling roller was established. The influence of roller speed on molten pool characteristics, cooling-roller heat transfer, and ribbon thickness was analyzed. The effect of ribbon thickness on the total loss and permeability of the magnetic cores was investigated. The results indicate that the molten pool size decreased as the roller speed increased. At t = 5 ms, the maximum heat-transfer coefficient of the roller surface increased from 2.09 × 10⁶ W·m⁻²·K⁻¹ at 15 m/s to 2.6 × 10⁶ W·m⁻²·K⁻¹ at 24 m/s. The ribbon thickness decreased from 39.96 μm to 20.02 μm (a 49.9% reduction) as the roller speed increased from 18 m/s to 30 m/s. The total loss of the nanocrystalline magnetic cores increased with ribbon thickness, whereas their permeability increased as ribbon thickness decreased. At 100 kHz, the nanocrystalline magnetic core made of 10–12 μm ribbons exhibited a high permeability of 59,507. Full article

In order to conduct a systematic study on the influence of the copper element on the soft magnetic properties of alloys, a series of alloy ribbons with compositions of Fe_90.70−xGd_2.32B_6.98Cu_x (x = 0.25, 0.5, 0.75, 1.0, 1.25, and 1.5) were fabricated via the single-roller melt-spinning method. The microstructure and magnetic properties of these ribbons were systematically characterized using X-ray diffraction (XRD), differential scanning calorimetry (DSC), and vibrating sample magnetometry (VSM). The research findings indicate that the introduction of the copper element significantly enhances the soft magnetic properties of the alloys. For the alloy ribbon with the optimized composition of Fe_89.95Gd_3.32B_6.98Cu_0.75, the saturation magnetization (B_s) attains 1.74 T. The improvement in performance is primarily attributed to the precipitation of the nanocrystalline α-Fe phase. This phase features fine grain sizes and relatively wide magnetic domain structures, which contribute to an increase in the saturation magnetization and a reduction in the coercivity, thus comprehensively optimizing the soft magnetic properties of the alloys. Full article

Hybrid atomization represents a novel method for powder production with high cooling and crushing capacities, but previous studies have primarily focused on tin and aluminum alloy systems. In present study, FeSiBNbCu nanocrystalline powders were prepared using a hybrid atomization system and the effects of atomization parameters on the sphericity of the powders and soft magnetic properties of the nanocrystalline magnetic powder cores (NMPCs) were investigated. Orthogonal experiments reveal that atomization pressure is the most critical factor affecting powder size, while melting temperature primarily influences sphericity. By optimizing the atomization parameters, the nanocrystalline powders with a high sphericity of up to 91.2% can be achieved, and the core loss at 1 MHz@20 mT of the corresponding NMPCs is reduced by 59.2% to 464 mW/cm³. This study provides valuable guidance for the fabrication of Fe-based nanocrystalline powders with excellent soft magnetic properties via hybrid atomization. Full article

This study explores the effects of sputtering pressure and power on FeCoNi high-entropy alloy films prepared by DC magnetron sputtering, focusing on microstructure, surface morphology, and static/high-frequency magnetic properties. In situ Lorentz TEM (LZ-TEM) was used to directly observe magnetic domain evolution. Results show that low sputtering pressure (1 mTorr) promotes strong FCC (111) crystallization, and smooth and dense surfaces. Increasing pressure leads to amorphization, higher roughness, and degraded magnetic performance. Under optimized pressure, 100 W sputtering power yields the best crystallinity, the smoothest surface, and optimal soft magnetic properties, including high remanence ratio, low coercivity, and clear ferromagnetic resonance in the 2–7.5 GHz range. The optimal parameters are confirmed as 1 mTorr and 100 W, producing uniform nanocrystalline FeCoNi films. In situ LZ-TEM reveals river-like domain walls, vortex–antivortex structures, and uniform magnetic moment precession, indicating weak domain pinning and excellent high-frequency magnetization consistency. This study provides experimental and theoretical support for the controllable fabrication of high-performance FeCoNi soft magnetic films for high-frequency devices. Full article