Microstructure and texture of the crystalline phase of steel for high-frequency welded pipelines X65 (2023)

Chemistry and physics of materials, volume 302, 2023, item 127762

This research aimed to control the size of gold nanoparticles (AuNPs) by monitoring the relationship between the pH stabilizer and the concentration of Au(III) in the resulting AuNPs. Through the synthesis of α-cyclodextrin (α-CD) and β-cyclodextrin (β-CD) AuNPs were used as stabilizers, which were reduced by o-hydroxybenzoic acid. Optimization based on CD and Au pH³⁺concentration, the optimal conditions for AuNPs with α-cyclodextrin (AuNPs-αCDs) are pH 11 and Au³⁺concentration of 180 ppm, while AuNPs with β-cyclodextrins (AuNPs-βCDs) at pH 6 and Au³⁺Concentration 180ppm. Dynamic light scattering (DLS) analysis results showed that AuNPs-αCD and AuNPs-βCD have a smaller size (12.89 and 13.10 nm, respectively) than 29.57 nm compared to those without CD (AuNPs-ortho). The results of X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS), zeta potential and stability test showed that AuNP-αCD have smaller size, higher crystallinity and better stability - βCD. AuNPs-αCD performed better than AuNPs-β-CD against Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa).

Materials Letters, Volume 333, 2023, Article 133672

Chromium carbide deposits with MC type primary carbides show a much lower susceptibility to cracking during welding. However, the traditional single-variable approach suddenly makes it difficult to optimize the composition and improve wear resistance. Here, we propose a method to speed up this process using experimental design and machine learning. A closed-loop design process was developed using existing data to predict future experiments and propose new experiments. The effect of Nb, V and Ti on pad hardness was determined in an active database. XRD analysis shows that Nb favors the formation of austenite in the matrix, while Ti favors the formation of martensite. The effectiveness of the method was proven by predicting the simultaneous effect of carbide-forming substances on the hardness of the coating, which indicates the possibility of using machine learning in the design of chromium carbide coating alloys.

Chemistry and physics of materials, volume 302, 2023, item 127760

Ammonium molybdate decomposition reaction for the preparation of molybdenum trioxide (MoO₃) is a key step in the production of molybdenum powder. In this study, the best MoO₃It is obtained by calcining the finest ammonium molybdate in an air atmosphere. Decomposition of the finest ammonium molybdate for the production of MoO₃It has been proven that it is a one-step reaction without intermediates in an air atmosphere. In addition, the effects of temperature and reaction time on the phase composition, morphology and particle size distribution of the product were investigated. The results showed that the temperature (350 ℃ ~ 450 ℃) had a significant effect on the reaction rate, and the time required to complete the decomposition reaction decreased with increasing temperature. However, the particle size of the generated MoO₃almost unchanged. It was also determined that the phase composition of the products in different layers (upper, middle and lower) was different, because the mass transfer of gaseous products in the layers affected the decomposition reaction. In addition, a kinetic model is proposed that takes into account the mass transfer of gaseous products in the material layer and the chemical reaction at the interface. Using the developed model confirms that the model describes the kinetics of ultrafine ammonium molybdate decomposition well.

Chemistry and physics of materials, volume 302, 2023, issue 127769

Niobium carbide (NbC) catalytic film deposited on the surface of a vanadium (V) substrate by reactive magnetron sputtering (RMS) using CH₄Creation of a composite NbC/V membrane for the separation and purification of hydrogen as a carbon source. The influence of CH₄Gas flow ratio (F_CH4= CH₄/(CH₄+Ar)) The phase structure, surface microstructure, catalytic efficiency of the NbC thin layer and hydrogen permeability of the NbC/V composite layer were investigated. The results showed that the structure of the NbC catalytic membrane changed from the dual phase of NbC and Nb to₂Single-phase cubic NbC after the addition of CH₄gas. Moreover, with increasing F_CH4, the carbon content of the NbC catalytic layer increased, but the crystallinity decreased. when f_CH4The hydrogen permeability of the NbC/V composite film is the highest when the concentration is 5% attributed to the appropriate carbon content and crystallinity of the NbC phase. Typically, the hydrogen permeability coefficient is 7.0 × 10⁻⁸Moore H₂Rice⁻¹Other⁻¹Per year^−0,5At 650°C, 2.4 times more than pure Pd.

Properties of Materials, Volume 195, 2023, Article 112502

Liquid metal embrittlement (LME) is a problematic phenomenon that occurs when reactive liquid metals attack the grain boundaries of ductile solid metals, causing brittle fracture under applied tensile stress. Despite extensive research efforts to understand LME, nuances related to the influence of initial microstructure on LME susceptibility and iron and zinc (Fe) destruction mechanismsZn) have not been thoroughly investigated. Previous studies on the susceptibility of microstructures to LME have given conflicting results or no correlation has been established between fracture susceptibility and failure mechanisms. In this study, steels with fully ferritic and austenitic microstructures were subjected to the same thermomechanical treatment to gain insight into how important features of the initial microstructure, such as grain boundary distribution and local chemistry, affect LME fracture susceptibility and failure mechanisms. The results show that both ferritic and austenitic microstructures are susceptible to LME crack formation. The ferrite microstructure is more prone to LME crack initiation, and the LME crack growth rate is relatively low, resulting in a higher frequency of smaller cracks observed in the samples. The austenitic microstructure is resistant to crack initiation, but has a much higher crack growth rate at LME, resulting in fewer cracks with much larger sizes. This leads to mixed ductile/brittle cracks in the ferritic microstructure, but fully intercrystalline brittle cracks in the austenitic samples. The results provide clear evidence of the susceptibility of ferritic and austenitic steels to LME cracking and can be used to guide microstructural modification strategies in the development of new methods for Zn-assisted LME crack removal in steels.

Chemistry and physics of materials, volume 295, 2023, issue 127098

A severely deformed Inconel 718 chip was age-hardened at 600°C for 10 hours to obtain a high proportion of γ^andSum up c^twoprecipitation. These nanometer-sized deposits help anchor the grain boundaries, thereby stabilizing the grain boundaries, preventing them from moving at high temperatures. This strong pinning effect at grain boundaries is expected to lead to increased strength and improved thermal stability. However, the presence of a large number of nanoprecipitates also causes precipitation hardening, which leads to limited plasticity of the material. Therefore, in order to improve plasticity, the precipitation-hardened chips were post-aging heat treated at 700°C, 800°C and 900°C for 15 minutes, hereinafter referred to as post-aging heat treatment. This high-temperature heat treatment is expected to increase dislocation mobility and lead to dislocation annihilation, thereby improving the plasticity of the aged samples. The results show that the recrystallization fraction increases with increasing heat treatment temperature after aging. It was found that heat treatment at 900°C produced a microstructure with the highest proportion of recrystallized grains, high proportion of overlapping lattice boundaries (CSL), relatively smaller grain size and better ductility. The results also show that during heat treatment after aging, two opposite effects occur simultaneously, which determines the possibility of increased dislocation movement and associated improvement in ductility. One of these effects is related to the retention force caused by the presence of sediment at the boundary. Higher confinement forces than fine precipitates prevent movement of grain boundaries, thereby inhibiting recrystallization and thus not improving ductility. The second effect has to do with the driving force of recrystallization. A higher driving force, especially in the highly stressed region of hyperfine shear, will favor a reduction in the total density of dislocations by recrystallization, leading to an increase in plasticity. The current study provides further insight into the competition between pinning and recrystallization in materials aged at elevated temperatures.