Explore the vast range of titles available.

A hot-forged Fe-30Mn-11Al-1C-10Ni (wt.%) low-density steel was developed, possessing a comparable strength-ductility synergy to those subjected to prior cold rolling and aging treatment. The initial microstructure after hot forging contained austenite matrix ( 70 vol.%) and a large fraction of B2 phases ( 30 vol.%) owing to the addition of high content of Al and Ni. The resultant dual-phase morphology effectively blocked the grain growth during hot forging, resulting in extremely fine grain size of both austenite (< 3 m) and B2 phases (< 2 m). In addition, dual precipitation of nano-sized -carbides and DO.sub.3 particles was formed during air cooling within austenite and B2 grains, respectively. Consequently, an excellent combination of strength (yield strength of 1250 MPa, ultimate tensile strength of 1381 MPa) and ductility (total elongation of 25%) was achieved in the hot-forged specimens owing to the synergy of the multiple strengthening mechanisms and excellent strain hardening capability. Particularly, the sequentially activated slip-band refinement in austenite and B2 phases and the hindering effect on dislocation movement of B2 phase provided a consistently high strain hardening rate, contributing to the superior strength-ductility balance. However, further aging treatment resulted in a gradual increase in strength but a severe loss in ductility, due to the formation of coarse intergranular -carbides. The present study suggests that an excellent strength-ductility synergy in Ni-alloyed low-density steel could be achieved through simple hot forging followed by air cooling.

Thermal protection materials with excellent performance are critical for hypersonic vehicles. Carbon fiber/phenolic resin composites (C[sub.f]/Ph) have been widely used as thermal protection materials due to their high specific strength and ease of processing. However, oxidative failure limits the extensive applications of C[sub.f]/Ph in harsh environments. In this paper, a novel hafnium carbide (HfC) and boron carbide (B[sub.4]C)-modified C[sub.f]/Ph was fabricated via an impregnating and compression molding route. The synergistic effect of HfC and B[sub.4]C on the thermal stability, flexural strength, microstructure, and phase evolution of the ceramizable composite was studied. The resulting ceramizable composites exhibited excellent resistance to oxidative corrosion and ablation behavior. The residual yield at 1400 °C and the flexural strength after heat treatment at 1600 °C for 20 min were 46% and 54.65 MPa, respectively, with an increase of 79.59% in flexural strength compared to that of the composites without ceramizable fillers. The linear ablation rate (LAR) and mass ablation rate (MAR) under a heat flux density of 4.2 MW/m[sup.2] for the 20 s were as low as −8.33 × 10[sup.−3] mm/s and 3.08 × 10[sup.−2] g/s. The ablation mechanism was further revealed. A dense B–C–N–O–Hf ceramic layer was constructed in situ as an efficient thermal protection barrier, significantly reducing the corrosion of the carbon fibers.

HfC[sub.x]N[sub.1−x] nanoparticles were synthesized using the urea-glass route, employing hafnium chloride, urea, and methanol as raw materials. The synthesis process, polymer-to-ceramic conversion, microstructure, and phase evolution of HfC[sub.x]N[sub.1−x]/C nanoparticles were thoroughly investigated across a wide range of molar ratios between the nitrogen source and the hafnium source. Upon annealing at 1600 °C, all precursors demonstrated remarkable translatability to HfC[sub.x]N[sub.1−x] ceramics. Under high nitrogen source ratios, the precursor exhibited complete transformation into HfC[sub.x]N[sub.1−x] nanoparticles at 1200 °C, with no observed presence of oxidation phases. In comparison to HfO[sub.2], the carbothermal reaction of HfN with C significantly reduced the preparation temperature required for HfC. By increasing the urea content in the precursor, the carbon content of the pyrolyzed products increased, leading to a substantial decrease in the electrical conductivity of HfC[sub.x]N[sub.1−x]/C nanoparticle powders. Notably, as the urea content in the precursor increased, a significant decrease in average electrical conductivity values was observed for the R4-1600, R8-1600, R12-1600, and R16-1600 nanoparticles measured at a pressure of 18 MPa, yielding values of 225.5, 59.1, 44.8, and 46.0 S·cm[sup.−1], respectively.

Carbon dioxide (CO[sub.2]) is a greenhouse gas, and its resource use is vital for carbon reduction and neutrality. Herein, the nucleophilic addition reaction of calcium carbide (CaC[sub.2]) to CO[sub.2] was studied for the first time to synthesize propiolic and butynedioic acids by using CuI or AgNO[sub.3] as catalyst, Na[sub.2]CO[sub.3] as additive, and triphenylphosphine as ligand in the presence/absence of a hydrogen donor. The effects of the experimental conditions and intensification approach on the reaction were investigated. The reactivity of CaC[sub.2] is closely associated with its synergistic activation by the catalysts, solvent, and external intensification, such as the ultrasound and mechanical force. Ultrasound helps to promote the reaction by enhancing the interfacial mass transfer of CaC[sub.2] particulates. Mechanochemistry can effectively promote the reaction, yielding 29.8% of butynedioic acid and 74.8% of propiolic acid after 2 h ball milling at 150 rpm, arising from the effective micronization and interfacial renewal of calcium carbide. The present study sheds a light on the high-value uses of CO[sub.2] and CaC[sub.2] and is of reference significance for the nucleophilic reaction of CaC[sub.2] with other carbonyl compounds.

Nanoscale carbides enhance ultra-strong ceramics and show activity as high-performance catalysts. Traditional lengthy carburization methods for carbide syntheses usually result in coked surface, large particle size, and uncontrolled phase. Here, a flash Joule heating process is developed for ultrafast synthesis of carbide nanocrystals within 1 s. Various interstitial transition metal carbides (TiC, ZrC, HfC, VC, NbC, TaC, Cr 2 C 3 , MoC, and W 2 C) and covalent carbides (B 4 C and SiC) are produced using low-cost precursors. By controlling pulse voltages, phase-pure molybdenum carbides including β-Mo 2 C and metastable α-MoC 1-x and η-MoC 1-x are selectively synthesized, demonstrating the excellent phase engineering ability of the flash Joule heating by broadly tunable energy input that can exceed 3000 K coupled with kinetically controlled ultrafast cooling (>10 4  K s −1 ). Theoretical calculation reveals carbon vacancies as the driving factor for topotactic transition of carbide phases. The phase-dependent hydrogen evolution capability of molybdenum carbides is investigated with β-Mo 2 C showing the best performance. Nanoscale carbides provide access to ultra-strong ceramics and show activity as high-performance catalysts. Here, the authors report a flash Joule heating process for the ultrafast, general synthesis of various transition metal carbides nanocrystals with phase controllability.

Due to the complex products and irradiation-induced defects, it is hard to understand and even predict the thermal conductivity variation of materials under fast neutron irradiation, such as the abrupt degradation of thermal conductivity of boron carbide ([B.sub.4]C) at the very beginning of the irradiation process. In this work, the contributions of various irradiation-induced defects in [B.sub.4]C primarily consisting of the substitutional defects, Frenkel defect pairs, and helium bubbles were re-evaluated separately and quantitatively in terms of the phonon scattering theory. A theoretical model with an overall consideration of the contributions of all these irradiation-induced defects was proposed without any adjustable parameters, and validated to predict the thermal conductivity variation under irradiation based on the experimental data of the unirradiated, irradiated, and annealed [B.sub.4]C samples. The predicted thermal conductivities by this model show a good agreement with the experimental data after irradiation. The calculation results and theoretical analysis in light of the experimental data demonstrate that the substitutional defects of boron atoms by lithium atoms, and the Frenkel defect pairs due to the collisions with the fast neutrons, rather than the helium bubbles with strain fields surrounding them, play determining roles in the abrupt degradation of thermal conductivity with burnup. Keywords: boron carbide ([B.sub.4]C); thermal conductivity; fast neutron irradiation

Refractory carbides are attractive candidates for support materials in heterogeneous catalysis because of their high thermal, chemical, and mechanical stability. However, the industrial applications of refractory carbides, especially silicon carbide (SiC), are greatly hampered by their low surface area and harsh synthetic conditions, typically have a very limited surface area (<200 m² g−1), and are prepared in a high-temperature environment (>1,400°C) that lasts for several or even tens of hours. Based on Le Chatelier’s principle, we theoretically proposed and experimentally verified that a low-pressure carbothermal reduction (CR) strategy was capable of synthesizing high–surface area SiC (569.9 m² g−1) at a lower temperature and a faster rate (~1,300°C, 50 Pa, 30 s). Such high–surface area SiC possesses excellent thermal stability and antioxidant capacity since it maintained stability under a water-saturated airflow at 650°C for 100 h. Furthermore, we demonstrated the feasibility of our strategy for scale-up production of high–surface area SiC (460.6 m² g−1), with a yield larger than 12 g in one experiment, by virtue of an industrial viable vacuum sintering furnace. Importantly, our strategy is also applicable to the rapid synthesis of refractory metal carbides (NbC, Mo₂C, TaC, WC) and even their emerging high-entropy carbides (VNbMoTaWC₅, TiVNbTaWC₅). Therefore, our low-pressure CR method provides an alternative strategy, not merely limited to temperature and time items, to regulate the synthesis and facilitate the upcoming industrial applications of carbide-based advanced functional materials.

In this comprehensive yet compact monograph, Michel W.Barsoum, one of the pioneers in the field and the leading figure in MAX phase research, summarizes and explains, from both an experimental and a theoretical viewpoint, all the features that are necessary to understand and apply these new materials.

Two-dimensional transition metal carbides (MXenes) have attracted a great interest of the research community as a relatively recently discovered large class of materials with unique electronic and optical properties. Understanding of adhesion between MXenes and various substrates is critically important for MXene device fabrication and performance. We report results of direct atomic force microscopy (AFM) measurements of adhesion of two MXenes (Ti 3 C 2 T x and Ti 2 CT x ) with a SiO 2 coated Si spherical tip. The Maugis-Dugdale theory was applied to convert the AFM measured adhesion force to adhesion energy, while taking into account surface roughness. The obtained adhesion energies were compared with those for mono-, bi-, and tri-layer graphene, as well as SiO 2 substrates. The average adhesion energies for the MXenes are 0.90 ± 0.03 J m −2 and 0.40 ± 0.02 J m −2 for thicker Ti 3 C 2 T x and thinner Ti 2 CT x , respectively, which is of the same order of magnitude as that between graphene and silica tip. The adhesion of two-dimensional transition metal carbides (MXenes) is important for potential MXene device fabrication and performance. Here, the authors show that adhesion of MXenes depends on their monolayer thickness and, in contrast to graphene, does not show number-of-monolayers dependency.

In this study, the influence of different process parameters on the macroscopic and microscopic morphology of the microgroove in the water-jet guided laser was studied. In addition, the microstructure evolution and material ablation mechanism of the microgroove were studied. The results show that with the increase in laser power, the depth of the microgroove increases from 154 μm to 492 μm, the width from 63 μm to 74 μm, and the depth-to-width ratio from 2.45 to 6.62; with the increase in scanning speed, the depth of the microgroove decreases from 525.33 μm to 227.16 μm, and the width from 67.61 μm to 71.02 μm, and the depth-to-width ratio from 7.77 to 3.20. With the increase in water jet pressure, the depth increases from 312.29 μm to 3.20. With the increase in water jet pressure, the depth increased from 312.29 μm to 362.39 μm, the width decreased from 71.59 μm to 62.78 μm, and the depth-to-width ratio increased from 4.38 to 5.77. In addition, the water guided laser processing of SiC[sub.p]/Al composites produces thermal–mechanical coupling and chemical reaction synergies: the material melts and vaporizes under the action of a high-energy laser beam, and the SiC particles are oxidized and thermally decomposed at local high temperatures due to their high thermal stability.