Resistivity Of Metals Research Articles

Multiple Metal-Nitrogen Bonds Synergistically Boosting the Activity and Durability of High-Entropy Alloy Electrocatalysts.

The development of Pt-based catalysts for use in fuel cells that meet performance targets of high activity, maximized stability, and low cost remains a huge challenge. Herein, we report a nitrogen (N)-doped high-entropy alloy (HEA) electrocatalyst that consists of a Pt-rich shell and a N-doped PtCoFeNiCu core on a carbon support (denoted as N-Pt/HEA/C). The N-Pt/HEA/C catalyst showed a high mass activity of 1.34 A mgPt-1 at 0.9 V for the oxygen reduction reaction (ORR) in rotating disk electrode (RDE) testing, which substantially outperformed commercial Pt/C and most of the other binary/ternary Pt-based catalysts. The N-Pt/HEA/C catalyst also demonstrated excellent stability in both RDE and membrane electrode assembly (MEA) testing. Using operando X-ray absorption spectroscopy (XAS) measurements and theoretical calculations, we revealed that the enhanced ORR activity of N-Pt/HEA/C originated from the optimized adsorption energy of intermediates, resulting in the tailored electronic structure formed upon N-doping. Furthermore, we showed that the multiple metal-nitrogen bonds formed synergistically improved the corrosion resistance of the 3d transition metals and enhanced the ORR durability.

Preparation of highly dewetted porous steel for shallow water AUV based on laser ablation method

Over the past two decades, autonomous underwater vehicles (AUVs) have been developed for various marine, commercial, and military applications. Porous metals, known for their lightweight high performance, suit AUV hulls, especially in shallow waters. However, because of their inherent hydrophilicity and porous structure, high humidity causes corrosion. In this study, a novel solution involving laser ablation and subsequent heat treatment of porous steel is proposed to improve the waterproofing performance both above and below water. By analyzing the surface structures, wetting attributes, and droplet behavior, the optimal laser and heat treatment parameters for superior performance are revealed. The porous nested structures created by laser ablation effectively reduce fog accumulation and, enhance the anti-fogging capabilities. Furthermore, the underwater stability ofsuperhydrophobic porous steels at different depths is systematically investigated. A method involving air injection into porous steel is proposed to address the limited air-pocket lifespan and instability of dehumidified surfaces. Experimental results confirm rapid and complete restoration of superhydrophobicity at a 0.9-meter depth. Thus, this study presents a practical corrosion-resistant surface material for AUVs in shallow-water environments and a new approach for achieving corrosion resistance in porous metals exposed to long-term aquatic conditions.

First-principles calculations on the intrinsic resistivity of realistic metals: a case study of monolayer V2N.

The Ziman resistivity formula is extensively employed to calculate the intrinsic resistivity of realistic metals using recent works of first-principles calculations. Owing to the approximation, Allen's generalization, which relates the solution of the Boltzmann transport equation (BTE) for metals to the transport electron-phonon (e-ph) spectral function, the applicability of the Ziman resistivity formula still needs to be discussed. In this work, we perform first-principles calculations of the intrinsic resistivity of the V2N monolayer, a kind of MXene material, by employing the Ziman resistivity formula and the iterative solution of BTE. We find that in the wide temperature range of 50-1400 K, the intrinsic resistivity of the V2N monolayer obtained by means of the two approaches, has the same order of magnitude. However the Ziman resistivity formula fails to correctly describe the Fermi level dependence of the intrinsic resistivity of the V2N monolayer. The underlying reason is that the band edge of the V2N and hence Van Hove singularity (VHS), is near the shifted Fermi level. We suggest a modified Ziman resistivity formula which is valid even if there is a band edge at the Fermi level.

Influence of MC Carbides on Pitting Corrosion Resistance of Weld Metal in Austenitic Stainless Steels

Influence of MC Carbides on Pitting Corrosion Resistance of Weld Metal in Austenitic Stainless Steels

Technological features of fusion welding of Al – Mg system alloys rationally alloyed with scandium

The results of the formation of macro- and microstructure of welded joints of aluminum alloy sheets of the Al– Mg–Sc system obtained by automatic argon-arc and electron-beam welding are presented. The mechanical characteristics of welded joints and weld metal under the types of welding used are given. Satisfactory weldability of the studied alloy by fusion welding methods is established with the provision of strength properties of welded joints at the level of 0.8...0.85 of temporary resistance of the base metal. The effect of the welding direction in relation to the rolling direction of the sheets on the mechanical properties of welded joints is studied. The destruction of welded joints during the tests occurred in the metal and fusion zone. The fractures are of a macro viscous nature with a viscous pit micro mechanism of destruction. The strength factor of welded joints of aluminum V-1579 alloy is at the level of 0.89 for automatic argon arc welding and 0.79 for electron beam welding.

Semimetallic electrical properties of rock salt-type LaBi thin films grown by solid-phase reaction of La/Bi multilayer precursors

Highly crystalline LaBi thin films, grown by solid-phase reaction of La/Bi multilayer precursors, showed metallic conduction and nonlinear Hall resistance, indicating the semimetallic nature with electron and hole carriers.

Optimization of Wire-bonding Process Parameters for Gold Wire and Aluminium Substrate using Response Surface Method

Wire bonding is a connecting technique that uses a combination of temperature, force, ultrasonic power, and time to attach two metallic materials, a wire, and a bond pad. In electronics, gold-aluminium (Au-Al) contact wire bonds are widespread due to corrosion resistance and great conductivity of both metals. However, due to the large contact-potential difference, the intermetallic compound growth at the metal’s interaction boundary has considerably worsened the advantageous properties of Au-Al intermetallic system. This intermetallic exhibit low toughness, and possibly low corrosion resistance, which would result in poor bonding quality. In this work, the materials used are 4x8 aluminium substrates and a 100-meter-long gold wire spool. This study aims to investigate the most optimised set of parameters to be used in Au-Al wire bond system, due to how problematic this system could have towards bonding quality. The experimental array was created using a response surface methodology (RSM)-based design of experiments. The effect of parameters and their significance to bonding quality in the Au-Al bond system were studied using analysis of variance (ANOVA). A correlation model was created for the wire bond strength data. The findings suggest that, within the range of parameters examined, the proposed correlation model can be utilized to predict performance measures. The optimum value of Au-Al wire bond system parameters was established at the time of bond at the first bonding site selected for 300 milliseconds (ms), wire looping height selected for 1200 micrometre (μm), wire bond Y-axis length selected for 996 micrometre (μm), and ultrasonic force at second bonding site selected for 300 milli Newton (mN). The outcomes of this research add to our understanding of the Au-Al wire bonding contact, in addition, to enhancing the wire bond's quality.

Strong Catalyst-Support Interaction in WOx Nanowires Supported Iridium Nanocatalysts: A Pathway to Efficient Water Electrolysis

This paper investigates the use of sub-stoichiometric tungsten oxide nanowires (WOxNW) as a support material for Ir nanocatalysts in the oxygen evolution reaction (OER) for proton exchange membrane water electrolysis (PEMWE). The results demonstrate that Ir@WOxNW has exceptional activity and durability, which paves the way for large-scale PEMWE deployment. The catalyst-support interaction plays a crucial role in explaining this performance boost.The preparation and characterization of Ir@WOxNW involved loading ultra-fine Ir nanoparticles onto WOxNW through hydrothermal treatment. High-resolution transmission electron microscopy (HR-TEM) and energy-dispersive X-ray spectroscopy (EDS) mapping analysis revealed that the iridium nanoparticles were uniformly loaded on the WOxNW support material, indicating efficient loading and dispersion. X-ray photoelectron spectroscopy (XPS) analysis showed that the supported Ir catalysts had a mixed valence state of Ir0 and Ir4+. Ir@WOxNW was compared with three other Ir-based OER catalysts, outperforming them in terms of activity and durability.The Ir@WOxNW catalyst demonstrated superior OER activity compared to the other three catalysts, with a mass activity of 812 A/gIr at 1.55 V vs reversible hydrogen electrode (RHE). The Tafel slopes of the OER catalysts were grouped into two categories: Ir Black and Ir@WOxNW showed smaller values (about 40 mV/dec), and larger values for Ir@ATO and Ir Oxide (about 120 mV/dec), respectively. Electrochemical impedance spectroscopy (EIS) measurements indicated that the high mass activity of Ir@WOxNW was due to a high population of catalytic sites with fast intrinsic kinetics from the dispersed ultra-fine Ir catalyst on WOxNW. The durability of all catalysts was investigated using an accelerated durability test (ADT), and the Ir@WOxNW catalyst demonstrated unexpectedly high durability compared to the other catalysts.The postmortem XPS analysis showed that the Ir@WOxNW catalyst exhibited a subtle change in Ir0/Ir4+ ratio after the ADT, indicating suppressed Ir oxidation and greater stability compared to the other catalysts. Additionally, non-destructive depth profile analysis by synchrotron based XPS was conducted on the supported ultrafine Ir catalysts before and after the ADT test. The difference in oxidation state increased as the supported Ir catalysts were probed deeper into the core. The results showed that after oxidation potential cycles ADT, the WOxNW-supported Iridium exhibited strong resistance to oxidation. The core location remained a high percentage of metal peak, in contrast to the other three control catalysts.Density functional theory calculations suggested that the oxygen-deficient WOxNW support helps to maintain the OER-active metal@metal oxide core@shell-like form of the Ir catalyst particles by enhancing electron transfer from the WOxNW to the Ir surface, thereby weakening the binding of oxygen to the Ir surface and enhancing the oxidation resistance of the Ir metal to oxides.In conclusion, ultrafine Ir nanoparticles supported on WOxNW have significant potential for practical applications in electrochemical water splitting. The high activity and durability of Ir@WOxNW make it a promising candidate for large-scale PEMWE deployment.

ACCELERATED TESTING OF MECHANICAL AND CHEMICAL EFFECT OF THE ENVIRONMENT ON WEAR RESISTANCE OF PARTS OF TRIBOCOUPLES UNDER COMPLEX DYNAMIC LOADING

The wear of tribocouplings parts under complex dynamic loading conditions is considered. A methodology for accelerated testing of friction pairs under multi-component dynamic loading is offered. The designs stand for modeling the processes of contact interaction, and studies of the wear resistance of tribocouplings, which operate under complexdynamic loading conditions with various lubricating and cooling media, are presented. The results of the impact assessment of mechanic and chemical transformations in the contact zone of tribological interfaces for wear resistance according to the developed method are presented. The variable effectiveness evaluation of the degradation influence products of macromolecular compounds in the composition of cutting fluid on wear resistance of metals in the contact zone of tribocouplings are analysed. The use ofthe presented materials allows rationally selecting friction pair materials for given operating conditions, developing new wear-resistant materials and coatings, lubricant composition and cooling mediums.

Heat Resistance of Transition Metals with an Aluminized Coating

Heat Resistance of Transition Metals with an Aluminized Coating

Effect of Anisotropy of Elastic Energy and Shear Waves on Electron–Phonon Relaxation and Electrical Resistivity of Noble Metals. Review 4

Effect of Anisotropy of Elastic Energy and Shear Waves on Electron–Phonon Relaxation and Electrical Resistivity of Noble Metals. Review 4

ANTI-CORROSION PROTECTION OF PIPELINES

Currently, in our country, the issue of protecting metals from corrosion has achieved high results, so there is a big gap between the achievements of scientific research in this direction and their use in industry. It is necessary to develop and implement highly effective methods of increasing the strength, corrosion resistance, heat and cold resistance of metals and alloys. Popularization, dissemination and implementation of effective methods of protection against corrosion and corrosive-mechanical destruction of machines, devices, equipment and metal structures are of great importance.
 During surface-plastic deformation, a chip is not formed, but a fine plastic deformation of the surface layer takes place. As a result, the surface layer is strengthened, wear resistance and resistance to corrosive environment increases. In many cases, the use of surface-plastic deformation makes it possible to increase the safety margin of parts working under variable loads by 1.5 to 3 times, and to increase the service life of parts. The paper examines directions for increasing the stability of parts of oil industry equipment by the method of surface plastic deformation, for resistance against various types of corrosion and corrosive-mechanical destruction.
 Fatigue is the phenomenon of gradual accumulation of material damage under the action of variable loads, which leads to changes in the properties of crack formation, their development and destruction. The processes of metal fatigue have been studied by many researchers, many hypotheses have been put forward, but the nature of fatigue remains largely unexplained.

Enhanced wear and corrosion resistance of the laser direct metal deposited AISI 316L stainless steel by in-situ interstitial N alloying

To meet the applicability in aggressive environments, the wear and corrosion resistance of additively manufactured 316L stainless steel can be improved by alloying with N. In this work, the in-situ interstitial N alloying of 316L with varying amount of CrxN is first manufactured at ambient environment utilizing the rapid cooling character of laser direct metal deposition (DMD). Combined effects of CrxN addition and DMD processing parameters on the relative density, dissolved N content, microstructure, microhardness, wear performance and corrosion behavior are systematically investigated. The results show that the relative density of the DMD 316L decreases with increasing additive amount of CrxN. A full density 316L sample with a high N content of 0.5 wt% is obtained. The N alloying transforms the solidification mode of DMD 316L from “AF” to “A”, resulting in a fully austenitic phase. The interstitial N promotes the formation of planar dislocations, nano-stacking faults and nano-twins during DMD. As the CrxN addition increases, both the microhardness (278–312 HV) and wear resistance are significantly enhanced owing to the dislocation strengthening and interstitial N solid solution strengthening. Compared with CrxN-free DMD 316L, the DMD 316L with CrxN addition presents superior pitting corrosion resistance. The increasing CrxN addition progressively improves the pitting corrosion resistance due to the positively synergistic effect Cr-N on the stability and repassivation ability of the passive film. This work provides a practical and cost-effective approach for manufacturing advanced 316L with exceptional properties.

The Effect of Sliding Speed on the Tribological Properties of Ceramic Materials

Ceramics are considered to be candidate materials for galvanising pot bearing materials due to their excellent corrosion resistance in many molten metals. Galvanising pot roll bearings must have excellent wear resistance, and, therefore, it is important to understand the wear behaviour of prospective bearing materials. This study investigates the friction- and wear-resistant properties of select ceramics, namely, pure hBN, BN M26, AlN-BN, Macor, 3YSZ, Al2O3 and Si3N4. The ceramics were tested at different sliding speeds using a pin-on-disc device equipped with SiC pins. The lowest coefficient of friction (COF) achieved was below 0.1, and it was measured for pure hBN at a 3.14 m/min sliding speed. However, a wear scar analysis showed that the BN grades suffered from severe wear. The highest wear rate was obtained for BN M26 at a 9.42 m/min sliding speed and was equal to 17.1 × 10−6 mm3 N−1 m−1. It was shown that the wear coefficient of the tested ceramics varied exponentially with hardness. The lowest wear was observed on the 3YSZ, Al2O3 and Si3N4 ceramics, which showed no volume loss, and, for this reason, they can be potentially used as bearing materials in continuous galvanising lines.

Insights from symmetry: Improving machine-learned models for grain boundary segregation

Grain boundary (GB) segregation substantially alters structural and functional properties of metallic alloys, including strength, fracture mode, and corrosion resistance. A critical factor causing the variability in the segregation of solute atoms at GBs is the atomic structure of the boundary. GB segregation and its link with GB structure should thus be included in modern computational strategies for polycrystalline materials design. Here, we first propose an efficient and user-friendly Machine-Learning (ML) framework capable of predicting the segregation of different solute atoms at grain boundaries in the form of a segregation energy density, from the corresponding undecorated GB atomic structure. We then show that ML provides a fresh and promising perspective to address the long-standing issue of GB structure-segregation property relationships, in the form of two correlated atomic parameters quantifying the degree of structural and segregation symmetry respectively.

Особенности формирования сварных соединений алюминиевого сплава АК9, полученного селективным лазерным плавлением

The problem of obtaining high-quality plate welds made of AL9 alloy and powder by selective laser melting is viewed. Welded butt joints of plates of AK9CH alloy with a thickness of 3.0 mm were made by melting welding (automatic argon arc and electron beam welding) and friction stir welding. After welding the base metal of the AK9 alloy plates and their welded joints were subjected to X-ray transmission, computed tomography, metallographic analysis and mechanical tests for static tension and static three-point bending. X-ray inspection of welded joints made by automatic argon arc and electron beam welding revealed multiple porosity inside welds. The nuclei of pores in the weld metal are spherical micropores, formed in the parent metal during selective laser melting. The diameter of these micropores is 150...200 microns. In the welding bath during fusion welding, micropores develop up to 420...1070 microns in diameter in case of argon arc welding and 215...420 microns in case of electron beam welding. Metallographic analysis of cross-sections of welded joints performed by fusion welding revealed a characteristic pore distribution in the weld metal. So in case of argon arc welding, the largest pores were located near the front surface of the weld. In the fusion zone at the border of the weld and the base metal, pores with a diameter of 80.220 microns were located in the form of chains along the entire thickness of the plates being welded. When testing welded joints for static tension, the destruction of joints occurred precisely in this zone. The strength coefficient of the AK9 alloy joints obtained by fusion welding is as follows: for automatic argon arc welding 0.46, for electron beam welding - 0.66. It is established that the problem of porosity of welded joints is eliminated when using solid -phase welding for jointing (friction stir welding). The strength coefficient of the jointing of the AK9CH alloy plates made by friction stir welding is at the level of 0.81.0.86 of the time resistance of the base metal. The destruction of welded joints occurs along the mixing zone. In the weld zone during friction stir welding, as a result of dynamic recrystallization, a fine-grained equiaxed structure with an average grain size of 4.5...6.2 microns was formed with virtually no pores. The parent metal is represented by a cellular structure in which there are pores up to 168 microns in size.

Epoxy Resin-Assisted Cu Catalytic Printing for Flexible Cu Conductors on Smooth and Rough Substrates.

Flexible copper conductors have been extensively utilized in flexible and wearable electronics. They can be fabricated by using a variety of patterning techniques such as vacuum deposition, photolithography, and various printing techniques. However, vacuum deposition and photolithography are costly and result in material wastage. Moreover, traditional printing inks require posttreatment, which can damage flexible substrates, or grafting polymers, which involve complex processes to adhere to flexible substrates. Therefore, this study proposes a facile method of fabricating flexible metal patterns with high electrical conductivities and remarkable bonding forces on a diverse range of flexible substrates. Catalytic ink was prepared by using a mixture of epoxy resin, copper nanopowder, and nanosilica. The ink was applied to a variety of flexible substrates, including a poly(ethylene terephthalate) (PET) film, polyimide film, and filter paper, using screen printing to establish a bridge layer for subsequent electroless deposition (ELD). The catalytic efficiency was significantly improved by treating the cured ink patterns with air plasma. The fabricated flexible metals exhibited excellent adhesion and desirable electrical conductivity. The sheet resistance of the copper layer on the PET substrate decreased to 9.2 mΩ/□ after 150 min of ELD. The resistance of the flexible metal on the PET substrate increased by only 3.125% after 5000 bending cycles. The flexible metals prepared in this study demonstrated good foldability, and the samples with filter paper and PET substrates failed after 40 and 70 folds, respectively. A pressure sensor with a bottom electrode consisting of a copper interdigital electrode on a PET substrate displayed favorable sensing performance.

Textile‐Based Stretchable Supercapacitors with Liquid Metal Current Collectors

AbstractStretchable supercapacitors (SCs) have attracted attention as energy storage devices for wearable electronics due to their excellent power performance, low heat generation, and ease of integration into clothing. This paper presents a stretchable SC composed of liquid metal current collectors on textile substrates. For the liquid metal and textile‐based supercapacitors (LM/Tex SCs), the wetting characteristics and electrical resistance of the liquid metal on different types of textile substrates are investigated. The wettability of the carbon nanotube suspension for an electrochemically active material is also affected by the chemical and structural properties of the textile substrates. The intrinsically stretchable LM/Tex SCs are fabricated by sandwiching a soft gel electrolyte layer between the two liquid metal and textile‐based electrodes. The optimized SCs based on the polyester/neoprene textile exhibit a high areal capacitance of 527.8 mF cm−2 and maintain more than 90% of their initial capacitance after 1000 repetitive stretching cycles. Finally, it is demonstrated that the LM/Tex SC is readily integrated into a shirt and reliably supplies electrical energy to light up a light‐emitting diode even under human motion.

Structure and tribological properties of “carbon steel – VC containing coating” compositions formed by non-vacuum electron-beam surfacing of vanadium-containing powder mixtures

Vanadium carbides are known as efficient reinforcing components for surface layers of steel parts. They provide good tribological characteristics of material under sliding friction conditions and against dry abrasive particles. Since wear conditions usually are quite severe, a thick coating is needed to provide the reliable protection of the part. The majority of currently used surfacing technologies ensure the coatings of insufficient thickness. For this reason, the non-vacuum electron beam cladding which is able to provide thick coatings is a reasonable alternative to other surfacing methods. This paper presents an analysis of the microstructure, micro- and nanohardness, elasticity, and tribological characteristics of coatings formed by non-vacuum electron-beam surfacing of vanadium and graphite-containing powder mixtures. In the course of the study, coatings with the average thicknesses of 1.8, 2.5, 2.6, 3.4 mm were formed on the surface of blanks made of medium‑carbon steel. Hardness of cladding layers was significantly improved compared to the low-carbon steel (by the factor of 5–7). The wear resistance of coatings under conditions of sliding friction was 5.8 times higher than the wear resistance of the base metal after quenching and tempering; the wear resistance of coatings under conditions of friction against fixed and loosely fixed abrasive particles was ∼2 and ∼4.8 times higher, respectively. Surface hardening of steel alloyed with vanadium and carbon derives from the presence of a martensitic matrix, ledeburite precipitates and a high volume fraction (14.5–29.5 vol%) of vanadium carbide particles of a dendritic form, which act as rigid barriers.

Influence of operating hours of water pipes in aggressive mediums to degradation of structural steel

Ruining the design of water pipelines can lead to negative economic and environmental consequences. The usual scientific, technical and technological developments to ensure reliable corrosion-mechanical resistance and durability of water pipelines are not sufficiently systematic, so there is no need to report the reasons, minds and mechanisms of corrosion-mechanical servicing. Laboratory and experimental investigations were carried out in relation to the operation of structural steels on the structure and instead of schoolhouses. The causes and mechanisms of degradation of metal structures due to routine operation in chemically aggressive technological media were studied. X-ray diffraction studies have established that, with increasing service life of pipes, the surface metal balls adsorb a significant amount of gases. It manifests itself especially strongly in the area of corrosion defects (stains, pittings). During regular operation, the metal walls of the pipes are heavily flooded, which leads to a hardening, increased hardness and decreased ductility. There is a significant change in the mass fraction of cementite in the metal, which indicates a decrease in the value of the material and a decrease in its resistance to corrosion-mechanical damage. Such research is a pioneer in the corrosion-mechanical resistance of metal and its degradation during heavy use in the presence of significant pressures and in the immediate presence of aggressive media.