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Additive manufacturing offers precise control over part geometry and material composition, making it ideal for creating functionally integrated materials (FIMs). A Ni-Al FIM was fabricated using directed energy deposition (DED) to investigate how local composition variations affect microstructure, precipitation, and mechanical behavior. Advanced microscopy characterization revealed a novel grain structure with distinct compositional regions and a composition transition interface. These distinct regions within a single grain led to abrupt changes in the deformation response, as demonstrated through in-situ micropillar compression. These findings underscore the potential of additive manufacturing to engineer material behavior at the microscale, advancing materials design and manufacturing.

Alloys of Ni–25Cr–(2Mn–1Si) under mixed deposits of ash + (0, 10, 50 and 90) wt% sulphate were exposed to an Ar–60CO2–20H2O gas at 650 and 750 °C for up to 300 h, forming both protective chromia and regions of Ni-rich oxide. The presence of ash + sulphate mixtures improved Ni–25Cr alloy protection, increasing surface coverage by thin, protective chromia compared with the deposit-free condition. Increasing sulphate proportions in these mixtures led to an accelerated chromia scale growth and reduced internal oxidation zone (IOZ). These beneficial effects were more significant at 750 °C, where surface coverage by the protective scale was increased, and a chromia band was formed beneath nonprotective regions at the IOZ-substrate interface. Alloy additions of Mn and Si generally slowed the growth of outer NiO and IOZ but did not lead to exclusive chromia scale formation. [ABSTRACT FROM AUTHOR]

This project studies the influence of different grain sizes of Ni-based Fe-33Ni-19Cr alloy obtained from heat treatment procedure on high temperature isothermal oxidation. Heat treatment procedure was carried out at two different temperatures, namely 1000℃ and 1200℃ for 3 hours of soaking time, followed by quenching in the water. These samples are denoted as T1000 and T1200. The heat-treated Ni-based Fe-33Ni-19Cr alloy was subjected to an isothermal oxidation test at 950℃ for 150 hours exposure. Oxidized heat-treated alloys were tested in terms of oxidation kinetics, phase analysis and surface morphology of oxidized samples. Oxidation kinetics were determine based on weight change per surface area as a function of exposure time. Phase analysis was determined using the x-ray diffraction (XRD) technique and surface morphology of oxidized samples was characterized using a scanning electron microscope (SEM). As a result, the heat treatment procedure shows varying grain sizes. The higher the heat treatment temperature, shows an increase in grain size with a decrease in hardness value. The oxidation kinetics for both heat-treated samples showed an increment pattern of weight change and followed a parabolic rate law. The oxidized T1000 sample recorded the lowest parabolic rate constant of 3.12×10–8 mg2cm–4s–1, indicating a low oxidation rate, thus having good oxidation resistance. Phase analysis from the XRD technique recorded several oxide phases consisting of Cr2O3, MnCr2O4, and (Ti0.97Cr0.03)O2 oxide phases. In addition, a uniform oxide layer is formed on the oxidized T1000 sample, indicating good oxide scale adhesion, thereby improving the protective oxide behavior.

The corrosion behavior of electrodeposited nickel-based coatings with W, Mo, and TiOx as potential catalytic material for hydrogen evolution reaction (HER) in highly aggressive media, 0.5 M H2SO4 and 6 M KOH, is presented. A wide range of electrochemical and spectroscopic methods have been used, such as linear sweep voltammetry, open-circuit potential (OCP), electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) to characterize the coatings before and after a residence time of 336 h in the model corrosion environment. The NiW alloy and the NiWTiOx composite coating demonstrate the best corrosion resistance in an acidic environment due to the stable tungstate phase formation (H0.33O3W and H2O4W) on the surface. In alkaline environments, all the systems studied show enviable resistance, but the alloys containing molybdenum stand out. [ABSTRACT FROM AUTHOR]

This project studies the influence of different grain sizes of Ni-based Fe-33Ni-19Cr alloy obtained from heat treatment procedure on high temperature isothermal oxidation. Heat treatment procedure was carried out at two different temperatures, namely 1000°C and 1200°C for 3 hours of soaking time, followed by quenching in the water. These samples are denoted as T1000 and T1200. The heat-treated Ni-based Fe-33Ni-19Cr alloy was subjected to an isothermal oxidation test at 950°C for 150 hours exposure. Oxidized heat-treated alloys were tested in terms of oxidation kinetics, phase analysis and surface morphology of oxidized samples. Oxidation kinetics were determine based on weight change per surface area as a function of exposure time. Phase analysis was determined using the x-ray diffraction (XRD) technique and surface morphology of oxidized samples was characterized using a scanning electron microscope (SEM). As a result, the heat treatment procedure shows varying grain sizes. The higher the heat treatment temperature, shows an increase in grain size with a decrease in hardness value. The oxidation kinetics for both heat-treated samples showed an increment pattern of weight change and followed a parabolic rate law. The oxidized T1000 sample recorded the lowest parabolic rate constant of 3.12×10-8 mg2cm-4s-1, indicating a low oxidation rate, thus having good oxidation resistance. Phase analysis from the XRD technique recorded several oxide phases consisting of Cr2O3, MnCr2O4, and (Ti0.97Cr0.03)O2 oxide phases. In addition, a uniform oxide layer is formed on the oxidized T1000 sample, indicating good oxide scale adhesion, thereby improving the protective oxide behavior. [ABSTRACT FROM AUTHOR]

Welds of the commercial Ni‐based alloys 602 CA, 699 XA, 601 and 690 were exposed under harsh metal dusting conditions. The pit formation was compared for as‐welded, brushed, ground, glass bead blasted, steel shot peened and dry cathodic pickled surfaces. Surface treatments were applied by industrial partners. When (stainless) steels were involved in the surface treatment, Fe contaminations acted as catalyst sites for pit initiation. A fast metal dusting attack was also observed on dry cathodic pickled samples. A beneficial effect was attributed to deformation of the sub‐surface zone, as it provides diffusion paths for oxide formers (by grinding and glass bead blasting). In the same region, formation of α‐Cr (BCC) precipitates was observed. The best performance was found for samples where the weld bead was fully flattened by grinding to P40 grit. In addition, it was demonstrated that on‐site slurry aluminization further enhances the resistance against metal dusting attack. [ABSTRACT FROM AUTHOR]

CH4-CO2 reforming reaction can convert two greenhouse gases, CH4 and CO2, into syngas with a theoretical n(H2)/n(CO) = 1, which is of great significance for the efficient utilization of natural gas resources and the realization of the two-carbon goal. Commonly used Ni-based catalysts for this process have good application potential due to their low cost and high activity. However, serious sintering and carbon deposits problems make them easy to be inactivated, and their stability cannot meet the industrial requirements. Adding another metal to Ni is an effective way to enhance the stability of Ni-based catalysts. In order to deepen the understanding of the mechanism of Ni-based alloy catalysts in the CH4-CO2 reaction and provide guidance for future research, the research progress of Ni-based alloy CH4-CO2 catalysts in recent years was reviewed. It is found that an appropriate amount of noble metals (Ru, Pt, Rh, etc.) or non-noble metals (Co, Fe, Cu, etc.) doping can effectively improve the sintering and carbon deposits resistance of Ni-based catalysts. On the one hand, noble metals themselves have excellent activity and stability, and on the other hand, they can also change the surface microscopic properties of Ni-based catalysts and play a synergistic role. Most of the non-noble metals themselves do not have significant catalytic activity, and mainly change the surface properties of Ni by forming alloys, thereby affecting the mechanism of reduction or reaction process. The mechanisms of improving the stability of Ni-based alloys are summarized as follows: inhibiting CH4 cracking by occupying the Ni step, adjusting the activation energy of CH4 and CO2 adsorption by changing the density of Ni metal atom electron clouds to promote the oxidation elimination of surface carbon, inhibiting sintering to improve the dispersity of active metals and inhibiting the nucleation of carbon deposits by changing the characteristics of surface atomic structure, etc. A deeper understanding of the surface microstructure characteristics and influencing factors of Ni-based alloys is an important research direction in the future. [ABSTRACT FROM AUTHOR]

In deep unconventional oil and gas development, the problem faced is that PDC bits are eroded by solid-liquid high-speed fluids, resulting in damage. It has led to serious damage to the stability of the drill bit, a decrease in the service life of the drill bit, and an increase in the difficulty in efficient drilling. The essence is that the surface hardness and erosion resistance of the drill bit are not strong enough. Therefore, improving the stability of drill bits is a crucial and urgent problem to be solved. In this paper, Ni60A + 20% WC + 0.3% graphene composite coatings were prepared on a Q235 steel substrate, which is a new type of high hardness coating. Moreover, the effects of microstructure and microhardness of the composite coatings at different laser powers (800 W, 1200 W, 1600 W, and 2000 W) were investigated. The results show that the laser power can significantly affect the microstructure of the coating. The phase composition of the composite coatings is essentially the same at different laser powers. However, there are significant differences in the content of each phase. When the laser power is higher than 1200W, the content of M23C6, Cr3C2 and Fe3C in the composite coating increases and the microhardness of the coating decreases. When the laser power is below 1200 W, the dilution rate of the substrate is low and a metallurgical bond cannot be formed between the composite coating and the substrate.

Ni-based alloys are promising materials for advanced nuclear reactors operating at high temperatures due to their exceptional resistance to high temperatures and corrosion. Understanding the synergy of phase stability and helium effects is crucial for assessing the long-term performance and reliability of these alloys in advanced nuclear reactors. This study has investigated the co-evolution behavior of M 23 C 6 precipitates and cavities in a boron-free solid solution strengthened Ni-based alloy GH3617 under high-temperature He ion irradiation, and its impact on alloy swelling and mechanical properties, by He ion irradiation experiments with the highest fluence of 1 × 1017 He/cm2 up to 800 °C. Transmission Electron Microscopy (TEM) and Nanoindentation are employed to investigate microstructural evolution and mechanical properties, respectively. The findings show that at room temperature and 500 °C, cavities and dislocation loops were the dominant irradiation defects, whereas at 800 °C, the density of cavities and dislocations reduced while the formation of M 23 C 6 precipitates increased. These precipitates act as effective trapping sites for He and point defect, leading to cavity formation at the interfaces or within the precipitates. Moreover, increased irradiation fluence accelerates the co-evolution process, resulting in an increase in the density and size of both precipitates and cavities, ultimately leading to enhanced swelling. The {111} planes are favored interfaces between intragranular M 23 C 6 precipitates and the matrix due to their minimal misfit, while the preferred interface planes between cavities with octahedral or cubo-octahedral shapes and the precipitate/matrix are also {111}, owing to their lower surface energy as well. The co-evolution of cavities and precipitates was found to influence mechanical properties, resulting in an irradiation hardening effect at lower fluences, while softening at higher fluences. This study provides novel insights into the degradation mechanisms of Ni-based alloys under coupling effect of He and high-temperature irradiation. • Co-evolution of M 23 C 6 precipitates and cavities were investigated in a boron-free Ni-based alloys GH3617 under high-temperature He ion irradiation. • The formation of M 23 C 6 precipitates and associated cavities was found at 800 °C. • Increased irradiation dose accelerates the co-evolution process of M 23 C 6 precipitates and cavities • The co-evolution of cavities and precipitates can resultin an irradiation hardening effect at lower fluences, while softening at higher fluences. [ABSTRACT FROM AUTHOR]

Utilisation of additive manufacturing (AM) for the fabrication of Ni-based alloys has seen a massive uptake in both academic and commercial institutions. However, processing of traditional Ni-based superalloys through AM has encountered numerous cracking issues. The primary forms of cracking include solidification, solid-state and liquation mechanisms. Many of these forms of cracking are influenced by the compositions, with certain Ni-based systems showing impressive resistance. The design of novel alloys systems specifically tuned for processing through AM might be necessary to realise the potential of these techniques. Recently, researchers have taken advantage of improved computational alloy design frameworks. These frameworks utilise methods such as neural networks to analyse massive volumes of data and predict compositions that might satisfy specific design criteria. [ABSTRACT FROM AUTHOR]

Hastelloy X is a typical solid solution strengthening superalloy featured by good tolerance against oxidation and adequate mechanical and creep properties at 900 °C. However, current works about Ni‐based superalloys mainly focus on the relationship between microstructure and mechanical performance at high‐temperature regions, leaving the failure mechanism under the circumstance of oxidation as an open issue. Herein, the effects of the microstructure on the high‐temperature oxidation behavior and mechanical properties of Hastelloy X alloys prepared by selective laser melting (SLM) technique and hot isostatic pressing (HIP), respectively, are investigated. The experimental results show the existence of a large number of microcracks in the SLM samples during oxidation at 900 °C, which can contribute to increased oxidation weight gain and ease of oxide layer exfoliation. With the assistance of HIP, thermal cracks are effectively eliminated by the combination of better elemental homogeneity. The further improvement of oxidation resistance is found to result from the densification of Cr2O3 particles and the hindrance of oxygen diffusion. From the perspective of the application, this work provides valuable support for the explanations of the oxidation resistance and fracture mechanism of Hastelloy X superalloys in high‐temperature service environments. [ABSTRACT FROM AUTHOR]

Electrochemical Impedance Spectroscopy (EIS) measurements were carried out in high temperature water with Ni-based Alloy-182. The aim was to correlate the EIS results with differences in Stress Corrosion Cracking (SCC) susceptibility that is present around the Ni-NiO transition. There was a clear difference between the EIS results at and away from the Ni-NiO transition. To make a more quantitative correlation a simple equivalent circuit was used to fit the experimental data. A clear correlation between the CPE exponent (n) and the SCC susceptibility could be obtained. Additionally, it was shown that the high frequency arc of the EIS data was related to the diffuse double layer

Abstract Here, heat treatment-dependent microstructural evolution and tensile properties obtained by uniaxial tensile test and small punch test (SPT) of the selective laser melting (SLM)-fabricated GH4099 alloy are investigated. The columnar grains characterized by predominant Cube texture exponent in the as-SLM condition transform into random-oriented recrystallized grains with profuse twins after solution treatment. Upon aging, dispersed nano-sized coherent γ' precipitates generate. Uuniaxial tensile test results indicate a balance of ultimate tensile strength (UTS) and uniform elongation in the aged sample, i.e., ∼1206 MPa and ∼ 21% vs. ∼948 MPa and ∼ 27% in the as-SLM sample. The present study highlights the predominant role of dispersed coherent γ' precipitates on the appreciable work hardening ability and hence better tensile property. The analysis of work hardening rate curves indicates the dislocation accumulation rate is comparable between the aged sample and the solution-treated sample, both of which are higher than that in the as-SLM counterpart. Appreciably, lower dynamic recovery rate exists in the aged alloy due to strong γ' particle-dislocation interactions, which favors higher work hardening rate among the three conditions. Nevertheless, the strong S, Rotated-Copper and Rotated-Goss components originating from preferential grain growth allow for uniform elongation decreased in the aged sample. Meanwhile, unified correlation equations between SPT and uniaxial tensile test are established for the present GH4099 alloy, which aims at providing an empirical relationship to evaluate tensile properties of the SLM-fabricated GH4099 alloy undergone various post-heat treatment. • A decent combination of UTS of ∼1206 MPa and uniform elongation of ∼21% is obtained in SLM-processed GH4099 after aging. • Dislocation accumulation rate and dynamic recovery rate change with heat treatments during tensile deformation. • Appreciable work hardening ability contributes to the good tensile property in aged GH4099. • Unified correlation equations between small punch test and uniaxial tensile test are established for the present alloy. [ABSTRACT FROM AUTHOR]

The purpose of the present study is to make clear the effect of material compositions on the corrosion behaviors in liquid tin (Sn). The corrosion tests of Fe, Fe-5Cr, 410 (Fe-12Cr), 430 (Fe-18Cr), 316L (Fe-17.3Cr-12.3Ni-2.2Mo-1.6Mn), Mo, Hastelloy C-276 (Ni-15.83Mo-15.67Cr-6.28Fe), Inconel 600 (Ni-15Cr-8Fe) and Inconel 625 (Ni-22Cr-9Mo-5Fe) were performed in liquid Sn at 773 K for 250 h. The Fe-Sn intermetallic compounds (IMCs) which were formed on the steels in liquid Sn were observed and analyzed by scanning electron microscope and energy-dispersive X-ray spectrometer. The thickness of the IMCs was thinner when Fe concentration of the steels was lower. The steels revealed smaller mass losses due to the corrosion when the Fe concentration of steels was lower. The dissolution ratio of Cr from the steels into liquid Sn was smaller than that of Fe. Hastelloy C276 corroded due to the dissolution of Ni and Cr in liquid Sn. However, Mo-rich layer was formed on the surface due to the dissolution of Ni and Cr into liquid Sn, and it mitigated the corrosion. Inconel 600 and Inconel 625 were severely corroded according to the formation of Ni3Sn4.

• Intermittent cooling effect during thermal cycling significantly influences the corrosion behaviour of alloys in Ar. • Thermal cycles in Ar was observed to reduce CR compared to isothermal conditions. • Ni-based alloys show better corrosion resistance than SSs at any conditions. Molten nitrate salts are widely used as heat transfer fluids and heat storage media for concentrated solar power (CSP) plants due to their favourable thermo-physical properties. The corrosion of alloys in nitrate salts used in CSP plants poses a critical challenge to the safety, cost and efficiency of their operations under high temperature. In this study, the corrosion behaviour of stainless steels; 321 and 347, and Ni-based alloy; IN 625 and In 825, in Solar (nitrate) salts has been experimentally investigated under isothermal (at 600 °C) and thermal cycling (between 600 °C and 250 °C) conditions, and under argon atmosphere. Corrosion assessment of test materials was achieved using gravimetric measurements in a simulated metal – molten salt environment in a furnace for 7 days. The micro-morphology and cross-sectional analysis of the corroding interface was carried out using a combination of scanning electron microscopy, energy dispersive X-ray spectroscopy and X-Ray diffraction techniques. Compared with isothermal condition, thermal cycling between the 250 °C (for 12 hrs) and 600 °C (for 12 hrs) reduces the corrosion rate of test materials, the severity of corrosion attack and the thickness of corrosion product layers. The result also shows that corrosion product breakdown due to spallation was also reduced by lower time at maximum temperature and cooling effect during thermal cycling, especially in stainless steels when compared with isothermal conditions at 600 °C. The spallation process became prominent with the formation of a Na-Fe oxide layer at the corrosion interface. Ni-based alloys show better corrosion resistance than stainless steels under both isothermal and thermal cycling conditions due to the superior passivation behaviour from combined Cr and Ni enrichment. Cr 2 O 3 and NiO were formed as an inner layer in a multi-layered corrosion products on the metal surface from reaction with oxygen. Oxygen was made available from the decomposition of nitrate ions at 600 °C. [ABSTRACT FROM AUTHOR]

Alloys of Ni-25Cr-(2Mn-1Si) under deposits of sulphate or ash + sulphate were exposed to a wet CO 2 gas with or without 0.5 vol% SO 2 at 650 °C for 300 h. Without SO 2 , multi-layered reaction products formed. Under sulphate, they were external NiO, inner NiCr spinel + Cr 2 O 3 band, internal oxidation zone and internal Cr x S precipitates. Under ash + sulphate, they were external NiO + Ni above the internal oxidation zone. Introducing SO 2 in the gas promoted alloy passivation, forming thin chromia scales under both deposits. Alloying with Mn and Si produced only minor improvements. These effects are examined in light of gas-deposit-alloy interactions. • Ni-25Cr-(2Mn-1Si) under deposits in wet CO 2 with or without SO 2 was investigated. • Sulphate accelerated NiO growth and led to internal Cr x S precipitation. • Loose ashes in the deposit enabled gas transport and limited sulphate-alloy contact. • SO 2 enhanced alloy passivation, forming a thin Cr 2 O 3 scale under the deposits. • Alloying Mn+Si was less effective than SO 2 in improving corrosion resistance. [ABSTRACT FROM AUTHOR]

Microstructure, hardness, precipitates and phase transformation on the X-Y surface of Inconel 718 Ni-based alloys fabricated by selective laser melting (SLM) were studied before and after a suitable heat treatment. The test results show that the obvious weld beads structure was observed on the surface of the as-built alloys, and the microstructure shows seriously inhomogeneous with distributing columnar crystals and fine dendrites. When the 720°C, 3 h/furnace cooling+620°C and 3 h/air cooling was used, the columnar and small dendritic crystals begun to transform into bulk crystals, and the weld beads structure disappeared instantly. The X-Y surface hardness of alloys is about HV490-540, which is higher than the one of other heat treatment processes. With the increase of solid solution temperature, the microstructure on the surface of alloys shows an obvious refining characterization. The hardness value on the surface was also reduced gradually. The typical columnar crystals, dendrites, intermetallic compounds and precipitated hardening phase (Cr-Fe-Mo-Ni, FeNi and Ni8Nb) were also reduced or could not be found. Under the solid solution process of 950°C, the fine homogeneous δ phase and γ′ phase in the grain or near the grain boundary had an important effect on the suitable surface hardness value (HV476-500) of alloys.

A nickel–indium (Ni–In) ferromagnetic alloy is successfully synthesized through a facile pulsed electrodeposition method. The composition, structure, and morphology are analyzed through atomic absorption spectroscopy (AAS), X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), and electron microscopy. The composition and structural analysis indicate fcc phase for the Ni43In57 and Ni63In37 alloys. The Ni–In alloy shows mixed phases when the Ni content is increased from 63 to 66 at%. Thermal analysis of the Ni63In37 results in an activation energy of 46 and 557 kJ mol−1 that can arise from the grain growth phenomena and phase transformation, respectively. Thermomagnetic studies show a Curie temperature of 340 °C for the Ni–In alloy with 63 at% Ni that also exhibits a saturation magnetization of 36 emu g−1. [ABSTRACT FROM AUTHOR]

Using laser cladding technology, a Ni60A alloy cladding layer added with rare earth oxides CeO2 and Cr3C2 was prepared on the surface of Cr12MoV die steel. Through scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) analyses, the influence of CeO2 on the microstructure, hardness and wear resistance of Ni60A–Cr3C2 laser cladding layer was studied, and the mechanism of action of CeO2 was discussed. The results show that in the laser cladding Ni60A–Cr3C2 coating, after adding CeO2 powder, the cladding layer is well formed and the microstructure is significantly refined. As the addition of CeO2 increases, the microhardness of the cladding layer increases first and then decreases. When the addition amount of CeO2 is 2 wt.%, the microhardness of the coating is the largest, which is 1107 HV. As the content of CeO2 continues to increase, the hardness decreases. As the content of CeO2 in the cladding layer increases, the wear loss of the sample first decreases and then increases. When the mass fraction of CeO2 is 1 wt.%, the wear loss of the cladding layer is the least and the wear resistance is the best. The wear morphology of the Ni60A + Cr3C2 cladding layer without adding CeO2 appears with a lot of abrasive debris, and the main mechanism is adhesive wear. When the addition amount of CeO2 is 1 wt.%, the wear mainly appears as furrow, which denotes abrasive wear. [ABSTRACT FROM AUTHOR]

Mechanochemical hydrogenation of acetylene on fragments of Ni-based alloys was investigated using planetary ball milling. Intermetallic compounds (IMCs) and solid solutions were employed as alloys. Among the alloys, NiAl and NiGa IMCs as well as Ni0.5Fe0.5 solid solution retained their crystal structures after the pulverization. The pulverization exposed fresh surfaces on which ethylene is adsorbed weakly compared to the monometallic Ni surface. [ABSTRACT FROM AUTHOR]

Oxidation-induced degradation of structural materials employed as exhaust valves within internal combustion engines (ICEs) will be a relevant life-limiting mechanism, in addition to creep and mechanical fatigue, due to ever-increasing severity of operating temperatures and pressures. Ni–Cr-based alloys, which form external chromia-based scales at the relevant operating temperatures are being considered as suitable candidate materials. Thermal cycling of these alloys in water vapor-containing atmospheres, such as those present during hydrocarbon fuel combustion within ICEs, can considerably influence their oxidation behavior. In this study, the role of typical alloying additions such as Mn, Si, Al and Ti on the cyclic oxidation behavior of model NiCr–X (X = Mn,Si,Al,Ti) alloys exposed in dry air and air + 10% H 2 O at 800 ∘ C and 950 ∘ C was investigated. Combined additions of Mn and Si reduced scaling rates compared to binary Ni–22Cr alloys. The presence of water vapor possibly suppressed formation of NiMnCr spinel and thereby the Cr depletion in the alloy. Combined Al and Ti additions mainly resulted in accelerated oxidation kinetics due to the Ti doping of chromia scales. More porous external scales were observed in water vapor leading to a much deeper depth of nitridation in the Ni–22Cr–Al–Ti alloys. [ABSTRACT FROM AUTHOR]

Robust and durable non‐precious metal electrocatalysts for the hydrogen evolution reaction (HER) are crucial to realize sustainable hydrogen production by electrocatalytic water splitting. In this work, a superhydrophilic NiCo nanoparticle array coupled with CeO2 is integrated on graphite plate (NiCo–CeO2/GP) by electrodeposition and subsequent high‐temperature selective reduction. The coupled CeO2 can accelerate dissociation of H2O and favor adsorption of hydrogen, prominently boosting the electrocatalytic HER activity of NiCo alloy. Also, the superhydrophilic self‐supported electrode can promote electron conduction, facilitate bubble release, and prevent catalyst shedding, ensuring an efficient and stable working condition. As a result, NiCo–CeO2/GP exhibits an outstanding HER catalytic activity with low overpotentials of 34 mV at 10 mA cm−2 and 140 mV at 500 mA cm−2, as well as remarkable durability in alkaline media. Notably, this catalyst activation strategy by CeO2 is also applicable to other Ni‐based alloys such as NiFe and NiCu, demonstrating its versatility. An alkaline electrolyzer with NiCo–CeO2/GP as cathode and the NiCo(OH)x–CeO2/GP precursor electrode as anode delivers a current density of 10 mA cm−2 at an ultralow potential (1.45 V@10 mA cm−2), surpassing that of the traditional Pt/C||RuO2 electrolyzer (1.54 V@10 mA cm−2). [ABSTRACT FROM AUTHOR]

The mechanical properties of Ni-based superalloys are based on the hardening gamma-prime phase with an ordered structure. A solution for new phase precipitate growth is suggested for the case of the Ni-based alloys. In accordance with solution a mathematical model of gamma-prime phase precipitates growth during direct laser deposition, which is a type of DED-method, was developed in order to be able to predict the size of the hardening gamma-prime phase grains and thus the mechanical properties of the alloy. A series of experiments on depositing samples using Ni-based superalloys powder was carried out to verify this model. [ABSTRACT FROM AUTHOR]

The paper shows the reasons for the growing demand for pipes made of materials with special properties, which include Ni-base alloy CrNi60WoTi. The article is dedicated to results of complex research of opportunity to improve outside surface quality of Ni-base alloy hot extruded pipe. The paper presents analysis of scientific and technical information to determinate the characteristic features of deformation of Ni-based alloys. In work presents the results of plastometric research of samples of metal from an alloy CrNi60WoTi, which made it possible to receive data of value of deformation resistance. According to the results of plastometric tests at the Gleeble 3800 thermo-mechanical process simulator using the module Hydrawedge, metal flow curves were constructed. Using the selected dependence in the work, an approximation of the experimental data is shown based on this information, in the article presents results of calculation technological parameters of pipe extrusion process. This information was used on the factory to product of pilot industrial batch of pipes with an improved quality of outside surface that meets the requirements of Technical conditions (TC) 14-3R-85 without turning the outer surface. [ABSTRACT FROM AUTHOR]

In this paper, the embedded-atom method was used to study the influence of different solute elements (Co, Cu, Yb) on the thermophysical properties of liquid Ni-based alloys. By exploring the relationship between surface tension, viscosity, diffusion coefficient and temperature of liquid Ni-based alloys with three solutes in the range of 1500 ~ 1900 K, we found that under certain components the surface tension of liquid Ni-based alloys with three solutes decreased as temperature increased. Except the case that the atomic radius of the same period decreased with the increase of the atomic number and influence of lanthanide and actinide contraction, the surface tension of liquid Ni-based alloys decreased with the increase of atomic number. The viscosity of liquid alloy showed a downward trend with increasing temperature, and the viscosity decreased exponentially with the temperature increasing under certain components. The variation trend of diffusion coefficient of the three kinds of atoms was similar to that of the temperature, which increased with the increase of temperature under the same component. Especially, the diffusion coefficient increases exponentially with the increase of temperature under certain components. These simulated data provided necessary thermophysical parameters for non-equilibrium dynamics analysis of liquid-phase alloys and also supplied a sound theoretical basis for exploring the internal physical mechanism of "liquid microstructures–thermophysical properties–preferred phase of nucleation". [ABSTRACT FROM AUTHOR]

• Thin wall parts of GH4169 and GH3536 superalloys were prepared by direct energy deposition. • The properties of the two superalloys before and after solution aging heat treatment were compared. • It provides some data support for the preparation of GH4169 and GH3536 functionally graded materials. In this study, thin-walled parts of GH4169 and GH3536 superalloys were prepared using the direct energy deposition (DED) method, respectively. The results revealed that solution aging treatment was effective in eliminating the boundary of the molten pool and refining the grain structure to some extent. Subsequently, the Laves phase redissolved in the γ matrix, releasing Nb element. This was followed by the formation of γ′, γ″, and δ phases, which effectively improved the yield strength and tensile strength of the GH4169 alloy after high temperature heat treatment. In the case of the GH3536 alloy, heat treatment caused a change in microstructure from columnar crystals to larger equiaxed crystals. Additionally, chain carbides precipitated at the grain boundaries, which increased the elongation after fracture but decreased the yield strength and tensile strength to some extent. Following solid solution aging treatment, the ultimate tensile strength of GH4169 deposited parts exhibited a 27.7% increase in the deposition direction and a 15.6% increase in the laser scanning direction. Conversely, the tensile strength of GH3536 showed minimal variations, but the elongation in both directions experienced notable improvements, rising by 22% and 20.7%, respectively. Solution aging treatment further eliminated the mechanical anisotropy of the two superalloys due to the inhomogeneity of microstructure and grains, as well as the existence of molten pool boundaries and grain boundary segregation. Furthermore, the microstructure and mechanical properties of GH3536 alloy were found to be better than those of GH4169 alloy, both before and after aging. [ABSTRACT FROM AUTHOR]

• Review theories and simulation approaches for electron and phonon thermal transport in metal alloys. • Present electrical and thermal conductivities of pure Ni and Ni-base alloys, from binary to quinary, depending on temperature and element compositions. • Discuss measured and calculated results of phonon dispersion and lifetimes of Ni-based alloys. • Discuss the effects of mass and interatomic force constant disorders on phonon thermal transport and lattice dynamics in Ni-based HEAs. • Suggest potential research topics to advance understanding of thermal transport in HEAs. High-entropy alloys (HEAs) including Ni and other 3 d transition metals present a unique class of materials characterized by single phase solid solutions in face-centered cubic structure with complicated chemical disorder, in terms of atomic size, mass, and force constants. While they are renowned for excellent mechanical properties in extreme environment, their thermal transport properties are underexplored, despite the importance in relevant applications. This article comprehensively reviews the experimental and theoretical research on thermal transport and lattice dynamics in Ni-based alloys focusing on HEAs, along with fundamental theories for electron and phonon thermal conductivity in metals and alloys. The influence of the disorders is discussed for Ni-based alloys, from binary to quinary, which particularly reveals the importance of the interatomic force constant disorder. Future research is expected to further advance the understanding of interactions between electrons and phonons and microscopic mechanisms of phonon transport, as well as methodologies for extreme environment. [ABSTRACT FROM AUTHOR]

The Ni57Nb33Zr5Co5 metallic glass is a promising alloy for bipolar plates in proton exchange membrane fuel cells. It is important to know which phase forms in this alloy under different cooling rates in order to understand its influence on the thermal stability and mechanical properties. In this work, melt-spun ribbons and rod samples with 1, 2 and 3 mm diameters were prepared and their phase formation, microstructure and mechanical properties were investigated by X-ray diffraction, differential scanning calorimetry, optical microscopy, scanning electron microscopy and microhardness. It is found that a completely crystalline structure forms in the lower cooling rate samples (2 and 3 mm diameter rods) with the presence of the equilibrium phases Ni3(Nb,Zr) and Nb7Ni6 as primary phases or as a very fine eutectic structure, while a fully glassy structure is attained in the samples with the highest cooling rate (ribbons). For the sample with an intermediate cooling rate (1 mm diameter rod), polymorphically crystals of an unknown metastable phase with spherical morphology precipitate in the glassy matrix with virtually the same composition as the matrix. The 2 mm diameter sample exhibits higher hardness than the other samples, which is attributed to its very fine eutectic colonies.

The aim of this study was to assess the long‐term impact that the addition of biomass provokes on superheater materials exposed to fireside corrosion environments. Alloys covering a broad range of commercially available materials were investigated. Their corrosion kinetics under different corrosive deposits and atmospheres was evaluated, and their corrosion products analyzed to deepen understanding of the underlying corrosion mechanisms. Therefore, three nickel‐based alloys and three austenitic steels containing 20–24 wt.% Cr were tested at 650°C for 7,000 hr. The long‐term exposure shows new mechanistic aspects of Type II hot corrosion that were revealed by accelerated material depletion. The formation of Ni–NiS eutectic and the formation of a Cr depleted zone close to the substrate corrosion product interface are indicative of the breakaway occurrence. Differences in the corrosion behavior are related to the balance of Ni, Mo, Co, and Cr and can serve as the material selection argument. The evaluation concluded with the finding that alloys presenting Mo and Ni might be preferentially used in fireside corrosion in the presence of biomass, whereas the use of austenitic steels suffer less corrosion if no biomass is present in the corrosive atmosphere. [ABSTRACT FROM AUTHOR]

A one-to-one correspondence is developed between the phase stability and corrosion resistance of the commercial (Ni-Cr-Mo)-based alloys C-276 and C-4. Alloy C-4 is shown to outperform alloy C-276 in acidic oxidizing media and approaches its resistance in acidic reducing media. Both alloys are found to have similar resistance to chloride-induced stress corrosion cracking in the annealed condition with short-range order. The aqueous corrosion resistance of both alloys is found to be improved by long-range order; however, they become highly susceptible to chloride-induced stress corrosion cracking. Alloy C-4 is distinguished by being stable toward precipitation of detrimental intermetallic compounds. However, alloy C-276 is shown to be prone to precipitation of mu phase which degrades its resistance to aqueous corrosion and chloride-induced stress corrosion cracking. It is concluded that the chemical composition of alloy C-4 is tailored to make it more versatile than alloy C-276 in acidic oxidizing media and the results are found to be consistent with the concept of atomic percent factor of each alloy. [ABSTRACT FROM AUTHOR]

Abstract Microstructural and surface characterization of Ni-based alloys viz. Alloy 690, Alloy 693 and Ni-17 wt.% Mo- 7wt.% Cr exposed to molten FLiNaK salt under air atmosphere at 973 K was carried out. Patches of mixed oxide layers of type NiO + Cr 2 O 3 , NiO + Al 2 O 3 +Cr 2 O 3 and MoO 3 + NiO + Cr 2 O 3 were observed for Alloy 690, alloy 693 and Ni-Mo-Cr alloy, respectively. Corrosion susceptibility index and calculated Cr diffusivity in the alloys followed the order: Alloy 690 > Alloy 693>Ni-Cr-Mo alloy. The oxide layers developed are only partially protective as they form a galvanic micro-couple with exposed surface which makes the later more prone to attack. The lower Cr depletion in case of Ni-Mo-Cr alloy as compared to Alloy 690 and 693 can be attributed to the fact that MoO 3 layer is formed over the areas devoid of oxide patches which may prevent/reduce galvanic coupling between Ni-,Cr-rich oxides and exposed surface. Highlights • Ni-based alloys exposed to molten FLiNaK salt under air atmosphere develop patches of mixed oxides at surface. • Alloy 690 and Alloy 693 developed mixed oxide layers of the types NiO +Cr 2 O 3 and NiO + Al 2 O 3 +Cr 2 O 3 , respectively. • These oxides formed galvanic micro-couples with exposed alloy surface leading to increase in Cr depletion from the alloy. • Ni-17 wt.% Mo-7wt.% Cr alloy formed MoO 3 +NiO + Cr 2 O 3 type mixed oxide layer. • A thin MoO 3 layer present on the exposed alloy surface reduces the effect of galvanic coupling thereby lowering Cr depletion. [ABSTRACT FROM AUTHOR]

A new class of polycrystalline gamma-prime strengthened superalloys with alloy compositions of (wt%) Ni-20Co-13Cr-6Fe-4Al-3W-2Mo-(4-x)Nb-(x)Ti (x = 0,1,2) were subjected to cyclic oxidation exposures in dry air at 800 °C for 3600 h. The alloys were borderline chromia/alumina formers, showing good oxidation resistance relative to commercially available materials of similar composition. While all alloys formed alumina scales initially, only the alloy with the lowest Ti/Nb ratio retained an alumina scale for the duration of the exposure. Formation of a continuous layer of rutile TiO 2 at the alumina/alloy interface is proposed to cause eventual alumina failure for the alloys containing Ti. • Ni-based high entropy superalloys subjected to cyclic oxidation in dry air at 800 °C. • Ti and Nb content varied from 0, 1, 2 wt% and 4, 3, 2 wt%, respectively. • All alloys formed alumina scales initially. • Eventual alumina scale failure occurred for alloys containing Ti. • Alumina scale failure associated with rutile TiO 2 formed at the alumina/alloy interface. [ABSTRACT FROM AUTHOR]

The microstructure in the Z-Y surface of Inconel 718 alloys fabricated by selective laser melting (SLM) shows the relatively homogeneous and irregular fine grain structure after the heat treatment process of 1050ºC solid solution + double ageing. A large number of bulk precipitates were observed on the grain boundary, and the typical dendritic crystallization and Laves phases disappeared. It is possible that a large number of δ phases (NbNi3) were precipitated on the grain boundary since the enrichment effect of element Nb. The hardness in the Z-Y surface increased from 350HV to 500HV, and the residual stress was transformed from the tensile stress to compressive stress.

Abstract The influence of temperature and pressure on the electronic, elastic, structural, and thermodynamic properties of Ni 3 Al alloy was investigated by performing a first-principles study. The calculated elastic constants, equilibrium lattice constants, and elastic modulus agree well with the recorded theoretical and experimental data. The calculated elastic constants indicate that C 11 is more sensitive than C 12 and C 44 to pressure. The Young's modulus, bulk modulus, and shear modulus increase with the increase of pressure. The ratio of bulk to shear modulus (B / G) and anisotropy factor A were also analyzed. The Debye temperature was obtained by calculating the elastic constants, and it changes with the change in the pressure. The thermal expansion coefficient, normalized volume, heat capacity, bulk modulus, and Debye temperature Θ D were determined and analyzed using the quasi-harmonic Debye model at pressures of 0∼60 GPa and temperatures of 0∼1600 K. Finally, the density of states and Mulliken population were investigated and the effect of pressure on these was analyzed. [ABSTRACT FROM AUTHOR]

Phase composition and structural features of nickel-based alloy EP741 obtained by high-speed direct laser deposition were discussed in the paper. The technology of high-speed direct laser deposition has been successfully applied during the formation of samples with the various operating parameters of the experimental device. The laser power was between 450 and 1200 W, the scanning speed was 1.2 mm/s, the powder feed rate was 45 g/min, and the laser beam diameter was 1.2 mm. The structure and phase composition of the initial material and as-deposited samples were studied using optical and scanning electron microscopy, x-ray analysis and transmission electron microscopy. The investigation has shown that spherical particles of powder (EP741) can be used to form products by additive manufacturing with the presence of additional heat treatment, since almost all the as-deposited samples obtained do not contain cracks, and large volume of pores was observed only in the sample obtained with the power of 450 W. In addition, the phase composition of the as-deposited samples showed a high content of precipitating phase Ni3(Al, Ti) in matrix, which is coherent to the solid solution based on nickel. In theory, the presence of Ni3(Al, Ti) phase corresponds to the heat-treated nickel-base alloy obtained by standard methods of processing. [ABSTRACT FROM AUTHOR]

Aiming at covering grain boundary (GB) with a geometrically close-packed (GCP) type intermetallic phase in Ni-based superalloys, GB precipitation behavior of the δ-Ni 3 Nb phase with the D0 a structure in the A1 matrix is investigated using a model alloy Ni-12Nb-3Fe. The D0 a phase precipitates on GB prior to grain interior (GI). The precipitation of D0 a phase tends to take place in a continuous manner above its nose temperature (1373 K) and in a discontinuous manner below the temperature. The area fraction of a GB covered by the precipitate ( ρ ) significantly differs by GB in aging at 1423 K, i.e. between 0 and 80% in short time aging and between 30 and 100% in long time aging, while their average area fraction ( ρ ¯ ) increases up to about 75% after long time aging. The observed large difference in ρ is found to be enhanced in the growth stage of the precipitation. A crystallographic orientation analysis indicates that the difference may be caused by the geometry of the habit planes, {111} in the matrix phase, with respect to the GB plane; that is, in the case that one of the habit planes is nearly parallel to the GB plane, the D0 a phase grows along the GB, resulting in high ρ , while the phase grows towards GI when any habit planes are inclined to the GB plane, resulting in low ρ . A multi-step heat treatment is proposed to suppress the growth of the precipitates towards GI. [ABSTRACT FROM AUTHOR]

One drawback of the laser powder-bed fusion additive manufacturing (AM) technique is the build-up of residual stresses during processing that requires a stress-relief heat treatment prior to components being removed from the build plate. Here, we demonstrate the coprecipitation of the γ″-phase alongside the known δ-phase, during stress-relief annealing of AM Inconel 625 at 870 °C. The unexpected precipitation of γ″ in the AM material is attributed to the local solute enrichment to the interdendritic regions of the as-built solidification microstructure. Dissolution of the δ and γ″ phases is achieved after annealing for 15 min at 1150 °C. [ABSTRACT FROM AUTHOR]

The aim of the work was to investigate corrosion resistance of highly alloyed steels and Ni-based alloys in a steam atmosphere for 1000 h at 700 °C. In these steam oxidation experiments, two solid solution strengthened alloys; Haynes® 230®, 617 alloy, two gamma-prime (γ′) strengthened alloys; 263 and Haynes® 282® and three Cr+Ni- rich stainless steels: 309S, 310S and HR3C austenitic steels were exposed. The study showed that the materials exposed commonly developed thin oxide scales; in Ni-based alloys, these consisted of mainly MnCr2O4 spinels and Cr2O3, with the exception of 617 alloy where NiCr2O4 spinels and Cr2O3 were found. In Fe-based alloys, Cr2O3, MnCr2O4 spinels, Fe,Mn(SiO)4, and finally Fe3O4 developed. No evaporation of chromia has been found within 1000 h test period. Furthermore, the development of TiO2 was not observed into a large extent in Haynes® 282® and 263 alloy, in contrast to the study performed at 800 °C under the same steam environment conditions. [ABSTRACT FROM AUTHOR]

Pure Ni and Ni-xCr (x = 7, 14, 22 and 27 wt%) binary alloys were exposed to supercritical-carbon dioxide environment at 600 °C and 20 MPa for 200 h. For pure Ni, a thick NiO layer was formed on the surface. Meanwhile, for Ni-7Cr alloy, an inner oxide layer consisted of rather irregular chromia and NiO was formed below the outer NiO layer. When Cr content was greater than 14%, a continuous chromia layer was formed, resulting in much lower weight gain and oxide thickness. However, amorphous carbon layers had developed along the oxide-matrix interface when chromia was formed. The presence of the carbon layer was explained in view of the high C activity corresponding to the low equilibrium oxygen potential of chromia. [ABSTRACT FROM AUTHOR]

Laser cladding Ni-based composite coating was fabricated on the surface of 42CrMo steel using 6 kW fibre laser. By the addition of Mo powder, a well-formed and crack-free laser cladding composite coating was obtained. The morphology, composition, microhardness and wear resistance of composite coatings were studied using a scanning electron microscopy, an energy-dispersive spectroscopy, an X-ray diffraction spectrum, a microhardness tester and a wear tester. The results show that the cladding layer has metallurgical bonding with the substrate. The main phases of Ni45 + 10%Mo laser cladding layer are (Fe, Ni), Cr23C6, Cr3C2, Mo2FeB2 and Cr2B3. After the addition of Mo powder, the size of the microstructure of composite coatings is finer than that of Ni45 cladding layer. Stubby-rod carbides are displayed in the interdendritic interface. The molybdenum and chromium are rich in the grain boundaries. The distribution of hardness is uniform in Ni-based cladding layer, and its microhardness is significantly higher than that of the substrate. Ni45 + 10%Mo composite coating has the best wear resistance. Its wear resistance reaches 1.734 times of Ni45 coating and 2.367 times of 42CrMo steel. [ABSTRACT FROM AUTHOR]