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GaAs surfaces require electrical and chemical passivation for semiconductor devices, but in order to have air stable passivation, high temperatures have been previously required in the passivation step. Here, we demonstrate air-stable, ex situ plasma passivation of GaAs using consecutive hydrogen and nitrogen plasmas at room temperature. No pre-clean using deoxidizing wet chemistry or other means is required. The hydrogen plasma step removes surface oxides and As, which leaves a Ga-rich layer that the nitrogen plasma then turns to GaN. The formed GaN layer efficiently passivates the surface. The plasma-passivated GaAs shows upto 5 × room-temperature photoluminescence after 1 year, and room-temperature time-resolved photoluminescence demonstrates robust passivation even after 3 years, both comparisons to similarly aged unpassivated GaAs. Atomic force microscopy was used to confirm that the passivated surfaces can be made smooth enough for microelectronic applications. Grazing incidence x-ray diffraction indicated that the nitride films are amorphous, and energy-dispersive x-ray spectroscopy was used to estimate the nitrogen content. We used a common inductively coupled plasma reactive ion etching system for plasma passivation, thus enabling the rapid adoption of this technique. [ABSTRACT FROM AUTHOR]

The virgin copper electrode has limited application due to its wear and mechanical properties using Electrical Discharge Machined (EDMed) on Inconel 718 superalloys. In order to enhance the performance of copper electrodes, in this work, Ion Nitriding (IN), Surface Hardening by Laser (LSH) and Hybrid Process (IN+LSH) are performed on copper electrodes to reduce the electrode wear in frontal and lateral. The electrode wear in the frontal and lateral of virgin copper electrode is processed and studied using EDM with varying pulse durations, current and Silicon Carbide (SiC) mixed EDM oil. The surface hardness in virgin and processed electrodes is also investigated. Overall analysis found that the hybrid technique produced a 59% higher hardness than that of virgin copper. The hardness in the EDMed surface was higher than that of the processed copper surface. A 1000μs pulse duration, 2 A current and 15 g/l SiC powder mixing EDM oil produced a low frontal wear in both virgin and processed copper electrodes. The electrode wear was reduced by 30% for frontal and 76% for lateral using a hybrid method. [ABSTRACT FROM AUTHOR]

Porous Si 3 N 4 ceramics with an interconnected pore structure were prepared by a paraffin emulsified suspension method. The effects of the volume ratio of paraffin to silicon and Y 2 O 3 addition on the structure and properties of porous Si 3 N 4 were studied. Uniform dispersed pores introduced by the emulsified paraffine droplets can be observed in the green samples. With the increase of the volume ratio of paraffin to silicon, the bulk density and the strength of the sample were decreased, and the apparent porosity and Darcy permeability were increased. The formation of α-Si 3 N 4 whiskers could be promoted by the addition of the Y 2 O 3 during the nitriding process, and numerous nano whiskers could be obtained in the pores left by the paraffine droplets with suitable addition of the Y 2 O 3. The porous Si 3 N 4 with interconnected whiskers prepared via the paraffin emulsion method exhibited potential application for hot gas particular matter filtration. [ABSTRACT FROM AUTHOR]

The nature of the support can fundamentally affect the function of a heterogeneous catalyst. For the novel type of isolated metal atom catalysts, sometimes referred to as single‐atom catalysts, systematic correlations are still rare. Here, we report a general finding that Pd on nitride supports (non‐metal and metal nitride) features a higher oxidation state compared to that on oxide supports (non‐metal and metal oxide). Through thorough oxidation state investigations by X‐ray absorption spectroscopy (XAS), X‐ray photoelectron spectroscopy (XPS), CO‐DRIFTS, and density functional theory (DFT) coupled with Bader charge analysis, it is found that Pd atoms prefer to interact with surface hydroxyl group to form a Pd(OH)x species on oxide supports, while on nitride supports, Pd atoms incorporate into the surface structure in the form of Pd−N bonds. Moreover, a correlation was built between the formal oxidation state and computational Bader charge, based on the periodic trend in electronegativity. [ABSTRACT FROM AUTHOR]

The nature of the support can fundamentally affect the function of a heterogeneous catalyst. For the novel type of isolated metal atom catalysts, sometimes referred to as single‐atom catalysts, systematic correlations are still rare. Here, we report a general finding that Pd on nitride supports (non‐metal and metal nitride) features a higher oxidation state compared to that on oxide supports (non‐metal and metal oxide). Through thorough oxidation state investigations by X‐ray absorption spectroscopy (XAS), X‐ray photoelectron spectroscopy (XPS), CO‐DRIFTS, and density functional theory (DFT) coupled with Bader charge analysis, it is found that Pd atoms prefer to interact with surface hydroxyl group to form a Pd(OH)x species on oxide supports, while on nitride supports, Pd atoms incorporate into the surface structure in the form of Pd−N bonds. Moreover, a correlation was built between the formal oxidation state and computational Bader charge, based on the periodic trend in electronegativity. [ABSTRACT FROM AUTHOR]

This work aims to evaluate the effects on surface hardness and wear resistance of plasma nitriding treatment on SAE 6160 steel that exhibits cathodic cage deposition of AISI 904L, with high nickel content and medium chromium content, varying the treatment time and temperature. The deposition temperature is 450 °C, and after deposition, the samples are nitrided at 450 and 500 °C for 2 and 4 h. All samples are characterized by X‐Ray diffraction, Vickers microhardness, optical microscopy, and wear resistance. The results show that for longer nitriding times and temperatures, there is the formation of the S phase, expanded austenite, and the precipitation of CrN, resulting in lower wear resistance among the nitrided samples, but considering that the resistance of all samples is higher to AISI 6160 samples. All samples show high surface hardness and a diffusion layer between 69 and 170 μm; the only deposited sample shows good resistance to wear due to the deposition efficiency of films based on Ni–Cr–Mo. [ABSTRACT FROM AUTHOR]

The given text is a compilation of research papers on various topics related to metallurgy and materials science. The papers cover a wide range of subjects, including new materials, physical metallurgy, process metallurgy, plastic processing of metals and alloys, and more. The papers provide valuable insights and experimental results in their respective fields of study. This document is a valuable resource for library patrons conducting research in the field of materials science and metallurgy. [Extracted from the article]

Among metallic biomaterials, AISI 316L has the cheapest price yet but the lowest mechanical properties and it is prone to corrosion. Bone plate failure is often triggered by dynamics load, crevice or pitting corrosion, or a combination of fatigue and crevice or pitting corrosion attack at the same time. Shot peening and plasma nitriding are surface treatments that enhance material properties. This work examined the shot peening duration effects and plasma nitriding on surface to the depth hardness, roughness, droplet contact angle, and fatigue life in environment containing rich chloride ions. The results revealed that shot peening and plasma nitriding improved both surface layer roughness and hardness. Furthermore, shot peening and plasma nitriding reduced droplet contact angle and enhanced the fatigue life of the material. [ABSTRACT FROM AUTHOR]

To manufacture metallic components with high wear resistance, treatments such as nitriding and carburising followed by quenching and tempering (NQT and CQT, respectively) are applied to various types of steel to increase the hardness (H) of the friction surface. However, the wear mechanism of the resulting functionally graded materials has not been fully understood. In this study, specimens of industrial 99.82% pure iron treated with NQT at 913 and 1033 K, and CQT at 1203 K, as well as hot-rolled sheets without heat treatment were examined by performing nanoindentation tests to measure changes in their H, reduced Young's moduli (Er), elastic deformation energies (We), and plastic deformation energies (Wp) along the depth direction. The relationship between Wp/We and the elastic strain resistance (H/Er) can be expressed for all specimens via the equation Wp/We = −1.0 + 0.16 (H/Er)−1. Furthermore, the obtained H/Er av measured at 5 µm intervals based on the specimen profile and wear volume has a good correlation depending to the sliding distance, as confirmed by the results of the ring-on-plate sliding tests conducted for the carbon-treated, nitrogen-treated, and hot-rolled specimens. This study provides a new approach, using H/Er parameters to identify the dominant factors affecting wear resistance at the initial stage of wear that may contribute to the development of wear-resistant materials. [ABSTRACT FROM AUTHOR]

Rationalizing material features according to the adopted synthetic strategy, aiming then to tune them on demand, is among the most relevant purposes of investigation in materials science. Herein, the systematic analysis of the dependence of graphitic carbon nitride (g‐C3N4) physical characteristics on the decomposition temperature of urea, rationalizing the impact of synthetic temperature on several characteristics of the materials (degree of N–H condensation, carbon vs nitrogen content, structural parameters, photoluminescence lifetime, surface area, pores volume), is discussed. g‐C3N4 nanostructures are fabricated by thermal decomposition of urea at different temperatures under ambient atmosphere, obtaining an almost ideal stoichiometry (C/N = 0.72) when setting the temperature at 600 °C. The samples show structural, textural, compositional, and optical differences directly depending on the fabrication temperature: specific surface area, pore volume and size, intralayer distance, and speed of radiative recombination of photogenerated charges are proportionally enhanced by increasing the synthesis temperature. The role played by all the physicochemical features of the prepared samples in promoting the catalytic degradation of Rhodamine B is investigated, highlighting their synergistic role in enhancing the catalytic efficiency. Significant differences in the dye degradation are recorded when using either UV or solar simulated light, demonstrating that Rhodamine B photosensitization rules the process. [ABSTRACT FROM AUTHOR]

The low-temperature plasma nitriding was utilized to describe the microscopic solid-phase separation in the austenitic stainless-steel type AISI316, induced by the nitrogen supersaturation. This nitrogen supersaturated layer with the thickness of 60 μm had a two-phase nanostructure where the nitrogen-poor and nitrogen-rich clusters separated from each other. Due to this microscopic solid-phase separation, iron and nickel atoms decomposed themselves from chromium atoms and nitrogen solutes in this nitrogen supersaturated AISI316 layer. These microscopic cluster separation and chemical decomposition among the constituent elements in AISI316 were induced in the multi-dimensional scale by the plastic straining along the slip lines in the (111)-orientation from the surface to the depth of matrix. The nitrogen solute diffused through the cluster boundaries into the depth. With the aid of masking technique, this nitrogen supersaturation and nanostructuring was controlled to take place only in the unmasked AISI316 matrix. The nanostructures with two separated clusters were mesoscopically embedded into AISI316 matrix after the masking micro-textures. This microscopic and mesoscopic structure control was available in surface treatment of multi-host metals such as superalloys and high entropy alloys. [ABSTRACT FROM AUTHOR]

Society of automotive engineers (SAE) 52100 (100Cr6) steel, used in manufacturing bearings and shafts, deserves attention due to wear and corrosion problems that cause machine losses in the industry. To solve these problems, heat treatments such as quenching and tempering are adopted to reduce wear mechanisms. However, in this work, the effect of these previous heat treatments on the final properties of plasma nitrided steel at three different temperatures (400, 450, and 500 °C) is evaluated. Surface hardness, tribological behavior, and corrosion resistance are evaluated. In the results of Vickers hardness, wear, and electrochemical analysis, it is shown that performing plasma nitriding at 400 and 450 °C on previously heat‐treated SAE 52100 steel provides better mechanical resistance and chemical integrity in a corrosive environment, making the studied steel more comprehensive for important industrial applications. [ABSTRACT FROM AUTHOR]

Graphitic carbon nitride (g-CN) has emerged as a promising visible-light-responsive photocatalyst, and its activity is highly sensitive to synthesis conditions. In this work, we attempt to correlate the photocatalytic activity of g-CN with its production yield, which is kinetically determined by the specific condensation process. Bulk g-CN samples were synthesized by the conventional condensation procedure, but in static air and flowing air, respectively. The one synthesized in static air showed a lower production yield with an increased specific surface area and preferential surface chemical states, corresponding to a significantly improved activity for photocatalytic hydrogen evolution (PHE) and dye degradation. We further synthesized a series of g-CN samples by merely changing the synthetic atmosphere, the ramping rate, and the loading amount of the precursor, and the difference in their PHE performance was found to be as high as 7.05 times. The notable changes in their production yields as well as the photocatalytic activities have been discussed from the point of view of polymerization reaction kinetics, and the self-generated NH3 atmosphere plays a crucial role. [ABSTRACT FROM AUTHOR]

The chemical composition, microstructure and properties of races of a foreign aircraft engine bearing are studied. The material and the heat treatment method are determined, the microstructure of the diffusion layer is analyzed, the thickness of the diffusion and effective layers is calculated, and curves of the distribution of hardness and residual stresses over the diffusion layer depth are plotted. The data obtained can be used for import substitution of heat-resistant bearings for aerospace applications. [ABSTRACT FROM AUTHOR]

Using the methods of advanced materials science, the structural-phase states and properties of multiple plasma-surfaced layers of the R2M9U steel formed in a shielding-alloying nitrogen environment on the 30HGSA steel are studied after its subsequent triple high tempering. It is found out that a framework-type structure is formed in the surfaced layer, wherein the base element is iron and the atoms of Mo, N, Cr, and V are localized in lengthy interlayers of the skeletal network formed by the carbide phase of different compositions. The atoms of Al are concentrated in the globular particles chaotically distributed in the surface layer volume. Both in the layer surface and in the zone of its contact with the substrate there are microcracks located along the phase boundaries. After the triple high tempering, the framework material structure is retained. A significant increase (a factor of 1.4) in the surfaced layer microhardness is revealed, which is attributed to the formation of a martensitic structure in the grain bulk, implying substructural strengthening of the material. The tempering is accompanied by a decomposition of the solid solution, followed by the formation of submicron-sized second-phase particles, indicating a dispersion strengthening mechanism. [ABSTRACT FROM AUTHOR]

Commercially available gray‐solidified cast iron exhibits reduced load‐carrying capacity under locally concentrated pressure with simultaneous sliding stress. Electron beam remelting dissolves the graphite near the surface, and the surface layer solidifies according to the metastable system. During subsequent gas nitriding, a dense compound layer forms on this white‐solidified, hard surface layer. The phase composition of the compound layer depends not only on the gas nitriding conditions, but also on the chemical composition of the cast iron. The effect of the individual processes of remelting and gas nitriding and their combination on the corrosion behavior of one ferritic and one pearlitic cast iron with different copper contents is investigated using potentiodynamic polarization measurements in 5% sodium chloride solution at room temperature. The remelted and nitrided surface layers exhibit the highest corrosion resistance. The proportion of iron carbonitrides γ' and ε contained in the compound layer influences the corrosion behavior. [ABSTRACT FROM AUTHOR]

Thermal conductivity (TC) of sintered reaction bonded silicon nitride (SRBSN) ceramics was predicted from process conditions using support vector regression (SVR) as a machine learning algorithm. A total of ten explanatory variables were selected from the process conditions for building a SVR model. The determination coefficient (R 2 ) in the testing results of the trained SVR model reached a satisfactory level (R 2 = 0.8 on average) when more than 100 data points were used as the training data. The relative importance scores of the explanatory variables revealed that sintering conditions (temperature and time) had the largest contribution to the TC prediction while those of oxygen impurity content in the main starting powder, types and concentrations of sintering additives and nitriding conditions were also influential to a certain extent. [ABSTRACT FROM AUTHOR]

This work demonstrates high-performance AlN/GaN double-barrier resonant tunneling diodes (RTDs) with high peak current density grown by plasma-assisted molecular beam epitaxy on c-plane free-standing GaN substrates, featuring stable and repeatable negative differential resistance (NDR) characteristics at room temperature. By scaling down the barrier thickness of AlN barrier and the lateral mesa size of collector, the record peak current density of 1551 kA/cm2 is achieved along with a peak-to-valley current ratio (PVCR) of 1.24, which is attributed to the reduced resonant tunneling time under thinner AlN barrier and the suppressed external incoherent valley current by reducing the dislocation number contained in the RTD device with the smaller size of collector. By statistically analyzing the NDR performance of RTD devices with different thicknesses of AlN barrier, the average peak current density increases from 145.7 to 1215.1 kA/cm2, while the average PVCR decreases from 1.45 to 1.1, correspondingly, accompanying with a decreased peak voltage from 6.89 to 5.49 V, with downscaling the AlN barrier thickness from 1.5 to 1.25 nm. The peak current density obtained in this work is the highest value among all the reported nitride-based RTDs up until now while maintaining high PVCR value simultaneously, which illustrates that ultra-scaled RTD based on vertical quantum-well structure and lateral collector size is a valuable approach for the development of nitride-based RTDs with excellent NDR characteristics and reveals their great potential applications in high-frequency oscillation sources and high-speed switch circuits. [ABSTRACT FROM AUTHOR]

The possibility of obtaining a composite material from a ferroalloy based on silicon, aluminum, and zirconium nitrides using self-propagating high-temperature synthesis is considered. It is shown that introducing up to 35% of a nitrogen-containing additive on the basis of ferroalumosilicozirconium to the initial ferroalloy leads to an increase in the nitrogen fraction, emission of the basic nitride phases in combustion products, deceleration of the combustion wave front, and reduction of the maximum combustion temperature. It is revealed that adding more than 20% of a preliminary nitrided material makes it possible to stabilize the combustion wave front propagation conditions and to obtain combustion products with a macroscopically homogeneous composition. Under the conditions of natural filtration of nitrogen, combustion of a powder mixture based on ferroalumosilicozirconium and a nitrided material yields a composite consisting of AlN, Si3N4, ZrN, and -Fe phases. [ABSTRACT FROM AUTHOR]

The development of a surface barrier discharge driven by a negative steplike voltage pulse with an amplitude of V = –8 kV in air at the atmospheric pressure and a pulse with an amplitude of V = –15 kV in nitrogen at a pressure of 6 atm is simulated numerically. Calculations for V = –8 kV were carried out using the local-electric-field and the local-electron-energy approximations. It is demonstrated that both approximations yield similar results on the dynamics of discharge development as a whole, the cathode-layer structure, and the field distribution at the front of the discharge. Substantial differences are observed in parameters of the discharge layer adjacent to the dielectric surface, which allowed to simulate an effect similar to filamentation of the discharge in nitrogen at a pressure of 6 atm and voltage of V = –15 kV in the local-energy approximation. [ABSTRACT FROM AUTHOR]

The ultrasonic impacting process was carried out on the fillet of 34CrNi3MoA steel crankshaft treated by quenching and tempering, medium frequency quenching and gas nitriding respectively, and the variations of surface integrity of crankshaft were analyzed. The results show that the Ra of fillet can be decreased to below 0.2 µm after the ultrasonic impacting. The ultrasonic impacted crankshaft with initial process of gas nitriding has the highest hardness but the lowest hardness increase rate due to its high deformation resistance of nitriding layer. The ultrasonic impacting can transfer the tensile residual stress to the compressive residual stress on the fillet, the specimens with initial process of gas nitriding exhibit the highest compressive residual stress of −412.17 MPa. The fatigue performance model of the crankshaft was established based on Basquin and Goodman equations, the crankshaft treated by gas nitriding and ultrasonic impacting is supposed to have the highest fatigue limit. [ABSTRACT FROM AUTHOR]

Fuel recirculation is a system configuration designed to improve the fuel utilization of fuel cells by recirculating the unreacted fuels at the outlet to the fuel inflow stream. In this study, fuel recirculation of a solid oxide fuel cell (SOFC) operated with ammonia is investigated. Recirculation operation results in a notable elevation of nitrogen content within the cell, originating from the decomposition of ammonia within the cell and subsequently reintroduced into the inflow stream. Therefore, the fuel flow rate needs to be increased to maintain the fuel utilization level the same as the base operation, which is an ammonia-fueled operation without recirculation. A multiscale model of an SOFC stack is used to compare the base operation and saturated level of the recirculation operation cases based on their polarization curves and distributions of ammonia, hydrogen, current density, temperature, first principal stress, and nitriding in the fuel electrode. The results show that overall stack performance, as reflected in the polarization curves, remains comparable between the base and recirculation operation cases. The power densities exhibit a difference of less than 2% between the base and recirculation operation cases. Moreover, it is indicated that the recirculation operation cases lead to more uniform hydrogen and current density distributions, lower temperature gradients, and lower thermal stresses. The results demonstrate that the recirculation operation cases lead to a reduction of up to 38% in the maximum tensile stresses within the fuel support layer. Nevertheless, these recirculation operation cases also induce nitriding across a larger portion of the active area. But as shown here this is a challenge that can effectively be addressed by applying nickel coatings to the inlet headers. • Overall stack performance remains comparable for the base and AOR operation cases. • AOR operation results in more uniform hydrogen and current density distributions. • AOR operation decreases temperature gradients, reducing thermal stresses. • AOR operation increases nitriding across a broader portion of the active area. • Mitigation of nitriding is achievable through nickel coatings over inlet headers. [ABSTRACT FROM AUTHOR]

The development of low-cost earth-abundant electrocatalysts to produce ammonia (NH3) with high efficiency for the nitrogen (N2) reduction reaction (NRR) remains challenging. Herein, we propose the development of highly efficient ultrathin nitrogen-vacancy-rich molybdenum nitride nanosheets (MoN-NV) for NRR using basic electrolytes under ambient conditions. In 0.1 M KOH, this catalyst attained a high faradaic efficiency (FE) of ∼14% with an NH3 yield of 22.5 μg h−1 mg−1cat at −0.3 V vs. a reversible hydrogen electrode under ambient conditions. The characterization results and electrochemical studies disclosed that nitrogen vacancies in the MoN-NV nanosheets played a critical role in the enhanced electrocatalytic activity for NRR. Furthermore, the recycling tests confirmed the stability of the catalyst during NRR electrolysis. [ABSTRACT FROM AUTHOR]

Operating solid oxide fuel cell (SOFC) stacks with ammonia induces the risk of nitriding in the fuel electrode and other metallic surfaces in the stack. This study aims to investigate the nitriding in the fuel electrode of an ammonia-fueled SOFC stack using a 3D Multiphysics model of a full stack. Based on the resulting species concentrations, a so-called nitriding potential is determined and compared to its critical level for various operating conditions and design modifications. The effects of the gas inflow temperatures, counter-flow configuration, and nickel coating over the inlet header of the stack are investigated. The results show that nitriding occurs in the first few centimeters of the fuel electrode for all investigated operating conditions considered in this study. Moreover, it is indicated that higher gas inflow temperatures and counter-flow configuration reduce the nitriding in the fuel electrode. Furthermore, the model illustrates the nitriding in the fuel active electrode for the gas inflow temperatures up to 700 °C. Finally, a significant reduction in nitriding in the fuel electrode is shown for a proposed nickel coating over the metallic inlet header due to a spreading of the ammonia decomposition. • Numerical investigation of Ni nitriding in an ammonia-fueled SOCF stack. • Nitriding occurs in the first few cm of the fuel electrode for base case operation. • Higher temperatures and counter-flow configuration reduce the nitriding. • Nitriding happens in the fuel active electrode for inflow temperatures up to 700 °C. • Nickel coating over the fuel inlet header reduces nitriding significantly. [ABSTRACT FROM AUTHOR]

A method of producing nitrogen-alloyed steel is considered. The nitrogen alloying technologies based on the use of nitrided ferromanganese and nitrogen purge gas are analyzed and compared to choose the most effective one for the TAGMET conditions. To produce SA 20A steel with a regulated nitrogen content (100–300 ppm), it is proposed to purge metal with nitrogen and argon during treatment in a ladle furnace and during and after degassing. Proprietary software controlling the purging of steel with nitrogen and argon from the control panel of the ladle furnace and the vacuum degassing unit has been developed. This ensured effective control of the nitriding process and achievement of the required nitrogen content in steel. Changing over from alloying with nitrided ferromanganese to purging with nitrogen gas made it possible to eliminate the pyroelectric effect and to reduce the secondary oxidation and contamination of steel with non-metallic inclusions. [ABSTRACT FROM AUTHOR]

The structure and properties of the surface and of the core of steel 08Kh18N10T-Sh subjected to radial forging and subsequent saturation by the method of ion-plasma nitriding are studied. It is shown that the complex deformation–ion-plasma treatment accelerates the nitriding process and provides a high level of strength of the surface and of the core of steel 08Kh18N10T-Sh. The lower the saturation temperature, the shorter the hold time and the higher the degree of the deformation of the steel, the more deformed α-phase capable to accelerate the saturation process is preserved in the structure. [ABSTRACT FROM AUTHOR]

In this study, the effect of different heat treatments on the microstructure and hardness of an X40CrMoV5-1 hot work tool steel used as a mold material was investigated. Heat treatment processes were applied as austenitization, cryogenic treatment and two-stage tempering at three different temperatures. After heat treatments, the microstructures of the samples were examined with a light microscope and RockwellC hardness was measured. Then, tribological properties were investigated by applying nitriding surface treatment with gas nitriding method to certain samples selected according to tempering temperature and cryogenic treatment condition. The effect of cryogenic treatment on the tribological properties of nitrided samples was investigated with the specific wear rate and microscopic examinations as a result of the dry friction wear test. The results showed that the tribological properties of the nitrided samples in terms of specific wear rate and wear mechanism were better in the deep cryogenic treatment applied sample. [ABSTRACT FROM AUTHOR]

This research presents a comprehensive analysis of deep neural network models (DNNs) for the precise prediction of Vickers hardness (HV) in nitrided and carburized M50NiL steel samples, with hardness values spanning from 400 to 1000 HV. By conducting rigorous experimentation and obtaining corresponding nanoindentation data, we evaluated the performance of four distinct neural network architectures: Multilayer Perceptron (MLP), Convolutional Neural Network (CNN), Long Short-Term Memory network (LSTM), and Transformer. Our findings reveal that MLP and LSTM models excel in predictive accuracy and efficiency, with MLP showing exceptional iteration efficiency and predictive precision. The study validates models for broad application in various steel types and confirms nanoindentation as an effective direct measure for HV hardness in thin films and gradient-variable regions. This work contributes a validated and versatile approach to the hardness assessment of thin-film materials and those with intricate microstructures, enhancing material characterization and potential application in advanced material engineering. [ABSTRACT FROM AUTHOR]

To solve the shortage of austenite phase precipitation caused by nitrogen loss in the welding process of UNS S2205 duplex stainless steel (DSS), shielding gas nitriding was investigated by adding different N2 contents in Ar shielding gas during the welding process. A good thin-walled pipe butt joint was formed using the pulsed tungsten inert gas (P-TIG) welding method with Ar-N2 shielding gas. High cycle fatigue tests of the weld joints were conducted to study the effect of shielding gas nitriding on the fatigue properties. Fatigue tests at three stress levels of 225 MPa, 270 MPa, and 360 MPa were carried out on the weld joints with different N2 contents, and the fatigue samples were all fractured in the high temperature heat-affected zone (H-HAZ). Within the current process parameters, the fatigue life of the 4 vol.% N2 welded joints was optimal. Fatigue striations appeared in the fatigue crack propagation zone, and the transient fracture zone was similar to the tensile fracture. Under the low-stress level, the area of the crack propagation zone under 4 vol.% N2 was the highest, the tear ridges all expanded around the crack source area, and the fatigue crack propagation zone presented a radial distribution. The proliferation and expansion of dislocations were mainly carried out in the austenite grains, and the dislocation density of the fatigue specimens under 4 vol.% N2 was smaller than that of the Ar specimens. Shielding gas nitriding effectively improved the balance of the two-phase ratio and the hardness of austenite phase, optimized the internal slip system, inhibited the proliferation of dislocations in the austenite phase, and improved the fatigue life of weld joints. [ABSTRACT FROM AUTHOR]

To enhance the wear resistance of TC4, the fabrication of a TC4/Co12/Ag self-lubricating composite coating was fabricated using laser cladding with N2 as the protective gas. The resultant composite coating demonstrates a crack-free and defect-free structure. The microstructure, phase composition, and hardness of the composite coatings were analyzed. At the same time, the anti-wear performance of the coating at different temperatures (room temperature (RT), 300 °C, 500 °C) and loads (10 N, 30 N) was systematically investigated. The results show that the in situ generation of TiN and the rapid solidification of the molten pool have an inhibitory effect on the diffusion of Ag. The uniform distribution of Ag with other phases resulted in small fluctuations in hardness. The average hardness reached 597.6 HV0.5. The load was increased from 10 to 30 N. The coefficient of friction decreased due to the increase in Ag diffusion. The wear resistance of the coating is superior to the substrate at different conditions, and the minimum wear rate is only 0.005 times of the substrate. The wear rate of the coating increased with increasing temperature at 10N, whereas the opposite trend was observed at 30 N. At RT, the coating experiences abrasive wear caused by Ag. When subjected to a temperature of 300 °C, the coating demonstrates a combination of abrasive and oxidative wear. At 500 °C, the predominant wear mechanism shifts to oxidative wear. [ABSTRACT FROM AUTHOR]

Low-temperature plasma nitriding of austenitic stainless steel can ensure that its corrosion resistance does not deteriorate, improving surface hardness and wear performance. Nevertheless, it requires a longer processing time. The hollow cathode discharge effect helps increase the plasma density quickly while radiatively heating the workpiece. This work is based on the hollow cathode discharge effect to perform a rapid nitriding strengthening treatment on AISI 304 stainless steels. The experiments were conducted at three different temperatures (450, 475, and 500 °C) for 1 h in an ammonia atmosphere. The samples were characterized using various techniques, including SEM, AFM, XPS, XRD, and micro-hardness measurement. Potentiodynamic polarization and electrochemical impedance spectroscopy methods were employed to assess the electrochemical behavior of the different samples in a 3.5% NaCl solution. The finding suggests that rapid hollow cathode plasma nitriding can enhance the hardness, wear resistance, and corrosion properties of AISI 304 stainless steel. [ABSTRACT FROM AUTHOR]

One of the best ways to obtain TiN coatings is through the nitriding process by efficient methods such as dense plasma focus (DPF). The gas composition of the nitrogen environment is a crucial factor affecting the properties of the coating. In this study, three different atmospheres of 100%N2, 50%N2–50%O2, and 75%N2–25%Ar were used to investigate their impact on the mechanical and biological properties of TiN coatings on NiTi substrate. The operating condition that yielded the coating with the highest hardness, as well as the lowest contact angle and Ni ion release, was chosen as the optimum condition. According to the XRD results, TiN was recognized as the dominant phase which causes high hardness and prevents Ni ion release. Moreover, surface analyses determined that the sample coated in 50%N2 composition possessed higher hardness and as a result displayed better mechanical properties. Also, the improved microstructural properties lead to an enhanced coating/substrate adhesion strength. On the other hand, the reaction of TiO2 and TiN lead to the formation of TiN0.6O0.4 ternary compound and for this reason, the 50%N2–50%O2 sample exhibited better performance in preventing the release of the toxic nickel ion compared to the other samples. Finally, due to the presence of TiO2 and TiN0.6O0.4 in the sample surface treated at 50%N2–50%O2, better hydrophilicity was observed compared to other samples. Results confirm that the applied surface modification method is effective in increasing the mechanical and biological properties of the NiTi, where it may open numerous possibilities for efficient use in orthopedic applications. [ABSTRACT FROM AUTHOR]

The paper studies the corrosion resistance of 40Cr130 in different structural states. The material is thus characterized in the annealed, normalized, quenched, tempered state and, respectively, following a thermochemical treatment. Good corrosion resistance was found in all states, and substantial improvements were noted following the thermochemical nitriding treatment. [ABSTRACT FROM AUTHOR]

Considering the relevance of Inconel 718 alloy for the oil and gas industry and the nature of the tribological system to define the friction and wear behaviors during sliding, this investigation presents results obtained in reciprocating tests under saline solution for active-screen plasma-nitrided Inconel 718. Bearing steel and silicon nitride ceramic were used as counterbodies, balls of 4 mm diameter. Extensive plastic deformation was confirmed using nanoindentation analysis, and oxidation governed the tribological responses when the steel ball was used as a counterbody. In these conditions, the presence of a nitrided layer was significant in reducing wear by one order of magnitude. On the other hand, when the ceramic ball was tested, abrasive wear was the primary mechanism, and the nitrided layer did not affect either the friction or the wear rate of Inconel 718. The corrosion behavior helped to confirm the predominance of described wear mechanisms. [ABSTRACT FROM AUTHOR]

It is necessary to explore new energy sources to alleviate the excessive demand for fossil energy. Water electrolysis is a promising means of sustainable hydrogen evolution. Herein, a Cu/NCF precursor was nitrized to prepare a nitrogen-doped carbon-coated multi-component NC@NiCoCu-N/NCF composite material. The good synergistic interactions among the three nitride phases, Cu3N, Ni4N, and Co2N, make H2O decomposition and H2 release more balanced during the reaction. The content and temperature were adjusted to explore the changes in the catalyst morphology and the trapezoidal nanosheets were transformed into a disordered rough coral-like nanostructure that facilitates better electrolyte penetration and provides more accessible active sites during the nitriding process. Nitrogen-doped carbon can enhance the conductivity of the catalyst, protecting the internal active structure from the erosion of the electrolyte and improving the structural stability. The NC@NiCoCu-N/NCF composite exhibited excellent hydrogen evolution performance and the overpotentials reached 89 mV and 131 mV under the current density of 10 mA cm−2 in 1.0 M KOH and 0.5 M H2SO4, respectively. Chronopotentiometry results indicated that the catalyst could operate continuously for at least 48 h and still maintain excellent structural stability. This study has great significance for the development of polymetallic or multicomponent catalysts designed to accelerate the field of hydrogen energy. [ABSTRACT FROM AUTHOR]

The structure, phase composition, wear resistance, and electrochemical behaviors of oxynitride films on the surface of austenitic 316L stainless steel substrates formed via plasma oxynitriding using gas mixtures of different compositions are studied. Plasma oxynitriding is carried out at a temperature of 425 °C for 2 h at various ratios of the gas mixtures, i.e., 25% O2 – 75% N2, 50% O2 – 50% N2, 75% O2 – 25% N2. The structure of the coatings is studied by scanning electron microscopy and x-ray diffraction. The wear resistance of the films is evaluated by sliding an alumina ball under dry conditions and in an SBF environment simulating body fluid conditions. The corrosion resistance of the films is determined in the SBF medium. It is shown that the formation of the S (111) and S (200) phase layer upon oxynitriding of steel 316L increases its wear and corrosion resistances. The films formed during the treatment at the gas ratio of 75% O2 – 25% N2, have the highest properties. [ABSTRACT FROM AUTHOR]

Using plasma surfacing in a nitrogen environment with a PP-R18U non-current-carrying flux-cored wire, the layers up to 10 mm thick were formed on a 30HGSA steel, followed by an additional high-temperature tempering (at 580°C for 1 hour in 4 tempers). It is shown that the deposited layer has a frame-type structure formed by α-iron grains with extended layers of the Fe3W3C (M6C) carbide phase located along the boundaries. Nanosized particles of carbides of the V4C3, Cr7C3, Fe3C, Cr23C6 and WC1–x types are identified in the grain volume. It is found out that high tempering increases the microhardness of the deposited PP-R18U layer by 13% (up to 5.3 GPa) and decreases its wear resistance by 12.3% the friction coefficient by 7.7%. [ABSTRACT FROM AUTHOR]

Nitrogen‐bearing K‐cymrite was synthesized in experiments at high pressures but so far has not been found/identified as inclusions in minerals subducted and subsequently exhumed from mantle depths. K‐cymrite is a potential carrier of nitrogen; it can store and transport up to 4 wt% of nitrogen in the deep mantle, thus contributing to the global nitrogen cycle. The stability of nitrogen‐bearing K‐cymrite synthesized at pressure of 6.3 GPa, upon exhumation to the Earth's surface, remains unknown. Here, we report an in situ Raman spectroscopic study of nitrogen‐bearing K‐cymrite, using Linkam heating and freezing microscope stage (THMS600). The transition induced in this experiment corresponds to the retrograde PT‐path of deeply subducted rocks. Our results demonstrate that (i) nitrogen‐bearing K‐cymrite structure is more stable upon heating than pure H2O bearing specimens (KAlSi3O8·H2O), (ii) phase transformation (e.g., H2O, N2, and NH3 release) starts at 550°C leading to the formation of kokchetavite (an anhydrous hexagonal polymorph of KAlSi3O8) frequently observed in high‐pressure metamorphic rocks, and (iii) Raman spectra of kokchetavite obtained from different precursors (e.g., nitrogen‐bearing and H2O‐bearing K‐cymrite) are identical. Thus, nitrogen‐bearing K‐cymrite can be considered a potential host phase for nitrogen in subduction‐related environments, and it can be preserved as inclusions in refractory minerals during the exhumation of deeply subducted rocks. [ABSTRACT FROM AUTHOR]

The effect of ion nitriding and nitriding in a melamine-based powder mixture on the structure and properties of AISI A290C1M steel was studied in the paper. Using ion nitriding made it possible to shorten the technological cycle's duration by 5–6 times compared to two-stage nitriding, optimize the diffusion layer's composition, provide a technologically simple process automation scheme, and improve the quality of nitride coatings. After the proposed mode of ion nitriding, a saturated layer depth of 0.25–0.32 mm, hardness up to 1000 HV, and an increase in wear resistance by 2.17 times were obtained. Using 95% melamine + 5% sodium fluoride during nitriding in a powder mixture significantly simplified the technological process. It did not require additional expensive equipment, which in turn significantly simplified the nitriding process with energy savings. The proposed technology and the composition of the mixture contributed to a significant acceleration of the nitriding process of AISI A290C1M steel, compared to traditional gas nitriding, and to obtain a hardness of the nitride layer of 970 HV and an increase in wear resistance by 2.6 times. A nitriding speed is explained by a significantly higher amount of atomic nitrogen when using melamine instead of ammonia and by the almost simultaneous disintegration of nanodispersed particles when the nitriding temperature was reached. After nitriding in a powder mixture, steel was subject to the slightest wear. [ABSTRACT FROM AUTHOR]

To improve the wear resistance of TC4 and mitigate surface cracking defects in laser cladding NiCrAlY/TC4 composite coatings, thermal boundary conditions were altered and in-situ generation of enhanced phase transition layers was employed during laser cladding. The microstructure, hardness, and wear behavior were characterized. The results indicated that the TC4/NiCrAlY anti-wear composite coating without cracking defects was manufactured by using insulation layer with the in-situ generation of enhanced phase transition layer technology and has the highest hardness and the best wear resistance. The highest hardness of TC4/NiCrAlY anti-wear composite coating is 653.56 HV0.5, which is about twice the hardness of the substrate (350 HV0.5), benefiting from the in-situ synthesis of reinforcing phases such as TiN and Ti2AlN. Comparative analysis showed coatings from natural convection, insulation, and in-situ synthesized transition layers possessed mean hardness values of 570.57, 620.91, and 653.56 HV0.5, respectively. Enhanced hardness resulted from altered thermal boundary conditions, extending the molten pool's existence, impacting grain size and nitride morphology, etc. Coatings crafted using insulation with in-situ transition layer exhibited minimal wear rates of 2.588 × 10–4 mm3/N m and 0.125 × 10–4 mm3/N m at room temperature and 500 °C. This was due to boundary condition changes fostering dendritic TiN formations, with the finely dispersed reinforced phase exhibiting heightened adherence. Furthermore, the relationship between wear performance and hardness was positively correlated at room temperature but not at 500 °C due to TC4's softening. The coating's wear mechanisms transitioned from abrasive and adhesive wear at room temperature to oxidative wear at 500 °C. [ABSTRACT FROM AUTHOR]

The study investigates the impact of microstructure modifications on the corrosion, passivation, and plasma-nitriding behaviour of 316L steel. Microstructure modifications are achieved through the laser powder bed fusion (L-PBF) process and surface mechanical attrition treatment (SMAT). Three scanning strategies (concerning the orientation of the sample surface with scanning directions) are used in the L-PBF process, and the corresponding samples are labelled as HNS (0°), INS (45°), and VNS (90°). The scanning strategies have altered the average grain size (maximum for HNS and minimum for VNS) and porosity (HNS has the highest). Porosity disappears after SMAT. The surface of the SMATed specimen (VS) has equiaxed austenite nanograins (∼32 nm) with a fine distribution of α'-martensite, nanotwins, and high dislocation density. Microstructure affects the passivation, corrosion, and nitriding behaviour of the steel. The VNS has the lowest corrosion rate, decreasing further after SMAT. The SMATed sample exhibits the lowest nitrided layer thickness (∼65 μm). SMAT followed by nitriding causes a gradient-structured layer (with improved hardness) consisting of a nitrided layer, SMATed layer, and core. The nitrided HNS sample (∼78 μm thick nitrided layer) is dominated by γ'-Fe4N, while the nitrided VNS and VS samples have a relatively higher proportion of expanded austenite. [ABSTRACT FROM AUTHOR]

The aim of this study was to determine the impact of the heating rate of steel balls made of AISI 52100 alloy steel on the kinetics and efficiency of the gas nitriding process when carried out using a chemical reactor with precise thermo-gravimetric measurements, which allowed for changes in sample mass during heating and nitriding to be monitored with an accuracy of 50 µg. In the chemical reactor, the examined alloy steel was subjected to a heating process at the selected nitriding temperature of 590 °C. Two heating variants were used: the first variant relied on heating to the nitriding temperature with different rates—1 °C per minute, 2 °C per minute, 5 °C per minute and 10 °C per minute, respectively—whereas the second variant relied on the fast—25 °C per minute—heating of treated specimens to a temperature of 475 °C, at which, the nitrogenous potential of the atmosphere promotes faster nitrogen diffusion deep into the nitrided substrate, followed by reheating up to the nitriding temperature at different rates: 1 °C per minute, 2 °C per minute, 5 °C per minute, and 10 °C per minute, respectively. To evaluate the impact of heating rate kinetics and effectiveness during nitriding on the obtained surface layer quality, we investigated the phase composition, microhardness distribution, and thickness of the obtained diffusion layers. It was found that heating to a temperature of 475 °C in the nitriding process does not significantly affect the average mass gain of a sample. Above this temperature, within the range of nitriding temperatures, the extension of time increases the sample's mass gain. Simultaneously, it was found that the use of a constant heating rate allows for thicker nitrided layers and a greater sample hardness to be obtained. Dual-stage heating, in turn, is more effective in the context of sample mass gain per time unit. [ABSTRACT FROM AUTHOR]

The application of titanium alloys is limited due to their low surface hardness and wear resistance, especially for parts operating under friction and contact loads. One of the most widely used technologies for the thermochemical treatment of titanium alloys is gas nitriding. A new method in this direction is surface plasma gas nitriding using indirect arc plasmatrons operating in a chamber with a controlled nitrogen atmosphere. In the present work, the changes in the phase transformations, microstructure, and surface hardness of titanium alloy Ti-8Al-1Mo-1V after plasma gas nitriding at the power of 18 kW, and 25 kW for a time between 5 and 30 minutes are studied. The plasma gas nitriding with the indirect plasmatron of the titanium alloy produced continuous surface layers. Analysis of the surface showed the presence of TiN and TiO2. The thickness of the plasma gas nitrided layers ranges between 100 μm and 350 μm, depending on the technological parameters. [ABSTRACT FROM AUTHOR]