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Precipitation hardening stainless steel (PHSS) possesses high strength, impact resistance, and corrosion resistance, making it extensively employed in aerospace, nuclear power equipment, and petrochemical industries. The precipitates and reversed austenite (RA) generated during heat treatment significantly influence the properties of PHSS. This study investigates the impact of aging temperature (480–620 °C) on PH 13-8Mo stainless steel. As the aging temperature increased from 480 °C to 620 °C, the yield strength (YS) and ultimate tensile strength (UTS) initially increased and then decreased, while the impact energy initially decreased and then increased. At an aging temperature of 510 °C, the strength and hardness reach their maximum values, indicating peak aging conditions. The microstructure after aging treatment is lath martensite, RA and NiAl. With increasing aging temperature, the size of NiAl precipitates increases, accompanied by a rise in RA content. The quantitative analysis assessed the contributions of various strengthening mechanisms (precipitation strengthening, solid solution strengthening, grain refinement strengthening, dislocation strengthening, etc.) to YS. Quantitative calculations revealed that the precipitation strengthening effect was most pronounced at an aging temperature of 510 °C. [ABSTRACT FROM AUTHOR]

This study reports the effects of post-annealing on the electrical reliability of a NiAl/SiO2 interconnect structure for potential use as post-Cu interconnect. Our materials characterization using transmission electron microscopy and secondary ion mass spectrometry discloses that annealing at elevated temperatures induced the diffusion of Al into SiO2: Al, for a 400 °C-annealed sample, diffused only to a few nanometers from the interface, forming a thin aluminum-rich oxide layer, while samples annealed at higher temperatures show an extensive Al diffusion and interfacial reactions. In a voltage ramp dielectric breakdown test, the 400 °C annealed sample shows the lowest breakdown voltage, possibly, due to the aluminum-rich oxide layer serving as a self-forming barrier while the samples annealed at higher temperatures display a drastic reliability degradation with the annealing temperature increasing. In addition, analyzing data acquired from time-dependent dielectric breakdown tests using the E-model helps us predict the lifetime of the 400 °C sample to be longer than 105 h at 1 MV/cm.

Intermetallic compounds with special physical and chemical properties are considered to be advanced materials. However, the brittleness at room temperature of intermetallic compounds leads to poor performance, which limits its widespread application in engineering. The objective of this study is to investigate the strengthening mechanism of the copper (Cu) on the microstructure and material performance of WC/NiAl/TiC composite coatings by the laser cladding process. The results reveale that Cu element has a significant effect on the microstructure evolution of the coatings by inhibiting coarse crystal formation. The refined microstructure of the layer had been realized. X-ray diffraction (XRD) analysis demonstrate a reduction in lattice spacing within the composite coating structure as the proper Cu is added. Furthermore, the addition of Cu contributed to an enhancement in microhardness (868.9 HV0.2) and wear resistance. With 3% copper been added, the wear loss of the coatings has been reduced by 81.13% and the average microhardness value has been increased by 1.4 times as well. Moreover, the chemical metallurgical bond is produced between the particles and bonding phase resulting in strengthened compactness within the layer acting as a physical barrier-like film that increases polarization resistance. [ABSTRACT FROM AUTHOR]

Due to their superior corrosion resistance at high temperatures, stainless steels have a wide range of applications in numerous industries (including chemistry, the petrochemical industry, the paper industry, and nuclear engineering), it is also utilized in the medical industry as an implant material. To enhance the outstanding qualities of stainless steel such as high temperature corrosion, surface coating methods are also used. Boronizing, nitriding, thermal spray coating, physical vapor deposition, chemical vapor deposition, and electro-spark deposition procedures are used to apply these coating processes to steel surfaces. The electro-spark deposition (ESD) coating technology is one of the most promising approaches in this area. Using high-frequency and high-current electric pulses, the ESD micro-welding procedure bonds electrode material to the surface of a metallic substrate. In this study, AISI 304 and AISI 316L stainless steels were coated with FeAl and NiAl intermetallics using the ESD method. First, suitable experimental parameters for ESD coating were established. Second, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the microstructures and phases that formed on the coated surfaces. Then, the surface hardness of the resulting layers was determined. Finally, the corrosion properties of intermetallic-coated stainless steels were determined using electrochemical methods and compared with each other. As a result, both the hardness values and corrosion resistances of both stainless steel sheets have increased with intermetallic coatings. [ABSTRACT FROM AUTHOR]

The effect of a minor amount of rare-earth element Nd addition (0.1 at%) on the microstructural properties, microhardness, and cyclic oxidation resistance of NiAl–Cr(Mo) alloy is investigated in detail. The microstructure of investigated alloys is composed of NiAl-based dendrites and a eutectic mixture whose components are NiAl and Cr(Mo) phases. The minor amount of Nd addition refines the microstructure and increases the microhardness considerably. The results of the cyclic oxidation tests reveal that the surface scales of both alloys are mainly consisted of α-Al2O3 and little amount of Cr2O3. A Cr(Mo)-rich layer is observed in the metal/oxide interface. With Nd addition, the oxidation resistance of Ni–33Al–31Cr–3Mo alloy is strongly improved. The Nd-added alloy exhibits lower oxidation mass gain and increased scale adherence. [ABSTRACT FROM AUTHOR]

A functionally graded composite NiAl-AlMg6 was prepared using the pressure of gaseous reaction products (impurity gases) produced during the synthesis of reactive powders in a sealed reactor. It has been shown that this method can be used to prepare a NiAl/AlMg6 composite with both chaotically oriented pores in the NiAl layer and unidirectionally oriented pores (lotus-type pores). The pore shape in NiAl was found to be dependent on the pressure of the impurity gases and hydrogen present in the starting titanium powder. A mechanism for pore formation in NiAl and AlMg6 composite during SHS is proposed. Thus, functionally graded high-temperature composites can be produced by SHS in a sealed reactor using the chemical reaction energy and the pressure of impurity gases and hydrogen. Additionally, minimizing the influence of impurity gases on the contact zone increases the interface area between NiAl and AlMg6. [ABSTRACT FROM AUTHOR]

By increasing the density of interfaces in NiAl–CrMo in situ composites, the mechanical properties can be significantly improved compared to conventionally cast material. The refined microstructure is achieved by manufacturing through electron beam powder bed fusion (PBF‐EB). By varying the process parameters, an equiaxed or columnar cell morphology can be obtained, exhibiting a plate‐like or an interconnected network of the (Cr,Mo) reinforcement phase which is embedded in a NiAl matrix. The microstructure of the different cell morphologies is investigated in detail using scanning electron microscope, transmission electron microscopy, and atom probe tomography. For both morphologies, the mechanical properties at elevated temperatures are analyzed by compression and creep experiments parallel and perpendicular to the building direction. In comparison to cast NiAl and NiAl–(Cr, Mo), the yield strength of the PBF‐EB fabricated specimens is significantly improved at temperatures up to 1,027 °C. While the columnar morphology exhibits the best improved mechanical properties at high temperatures, the equiaxial morphology shows nearly ideal isotropic mechanical behavior, which is a substantial advantage over directionally solidified material. [ABSTRACT FROM AUTHOR]

Zero-dimensional structure, unique mechanical properties and potential thermal and chemical stability of nanodiamond (ND) make it a wise choice for reinforcement in metal matrix composites. Current study reveals the corrosion resistance (CR) of ND (0-1 wt.%)-reinforced Nickel-Aluminum (NiAl) coatings fabricated using atmospheric plasma spraying. The phase examination and microstructure demonstration of the powders and coatings were carried out using various characterization techniques, such as x-ray diffraction, Transmission Electron Microscopy, Scanning Electron Microscopy etc. Further, x-ray photoelectron spectroscopy reveals the retention of ~ 69% sp3 hybridized ND in the coating. The electrochemical tests in 3.5 wt.% NaCl solution reveals that 0.1 wt.% ND-reinforced NiAl coating demonstrated the best CR among all coatings, with a CR value of 0.16 mpy, which is ~ 5 times better than pristine NiAl coating. This improvement is ascribed to the minimization of defects in the coating after reinforcement and formation of stable passive film in the immersed situation. However, increasing the ND content masked its benefits and on contrary, resulted in increased CR due to predominantly acting micro-galvanic corrosion. Post corrosion characterizations approaches were made to validate the after corrosion results and have been discussed in details. [ABSTRACT FROM AUTHOR]

The scientific goal of this paper is to study and explain the relationship between the microstructure of a ceramic–intermetallic composite fabricated by consolidating a mixture of Al2O3 and NiAl-Al2O3 using the PPS technique and its basic mechanical properties. Six series of composites were manufactured. The obtained samples differed in the sintering temperature and content of compo-powder. The base powders, compo-powder, and composites were investigated using SEM equipped with an EDS and XRD. Hardness tests and KIC measurements were applied to estimate the mechanical properties of the fabricated composites. The wear resistance was evaluated using a "ball-on-disc" method. The results demonstrate that the density of the obtained composites increases with the increased temperature of the sintering. The content of NiAl + 20 wt.% Al2O3 did not have a determining effect on the hardness of the manufactured composites. The highest hardness, contacting 20.9 ± 0.8 GPa, was found for the composite series sintered at 1300 °C and 2.5 vol.% of compo-powder. The highest KIC value from all the studied series equaled 8.13 ± 0.55 MPa·m0.5 and was also achieved for the series manufactured at 1300 °C (2.5 vol.% of compo-powder). The average friction coefficient during the ball-friction test with the Si3N4 ceramic counter-sample was between 0.8 and 0.95. [ABSTRACT FROM AUTHOR]

It is challenging to design one non‐noble material with balanced bifunctional performance for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) for commercial sustainability at a low cost since the different electrocatalytic mechanisms are not easily matchable for each other. Herein, a self‐standing hybrid system Ni18Fe12Al70, consisting of Ni2Al3 and Ni3Fe phases, was constructed by laser‐assisted aluminum (Al) incorporation towards full water splitting. It was found that the incorporation of Al could effectively tune the morphologies, compositions and phases. The results indicate that Ni18Fe12Al70 delivers an extremely low overpotential to trigger both HER (η100=188 mV) and OER (η100=345 mV) processes and maintains a stable overpotential for 100 h, comparable to state‐of‐the‐art electrocatalysts. The synergistic effect of Ni2Al3 and Ni3Fe alloys on the HER process is confirmed based on theoretical calculation. [ABSTRACT FROM AUTHOR]

This letter reports on the study of employing an Al capping layer to improve the thermal stability of NiAl films for advanced interconnect applications. We prepare NiAl films with an Al capping layer of various thicknesses. Transmission electron microscopy analysis of NiAl with a 1 nm thick capping layer annealed at 450 °C discloses an effective suppression of Al out-diffusion from the NiAl layer and hence enhanced thermal stability. Measurement of thickness-dependent resistivity unravels a much slower resistivity increase for the capping layer sample than that of the sample without capping layer and low resistivity below 10 nm (49.7 μ Ω·cm for 3.2 nm). [ABSTRACT FROM AUTHOR]

A functionally graded composite NiAl-AlMg6 was prepared using the pressure of gaseous reaction products (impurity gases) produced during the synthesis of reactive powders in a sealed reactor. It has been shown that this method can be used to prepare a NiAl/AlMg6 composite with both chaotically oriented pores in the NiAl layer and unidirectionally oriented pores (lotus-type pores). The pore shape in NiAl was found to be dependent on the pressure of the impurity gases and hydrogen present in the starting titanium powder. A mechanism for pore formation in NiAl and AlMg6 composite during SHS is proposed. Thus, functionally graded high-temperature composites can be produced by SHS in a sealed reactor using the chemical reaction energy and the pressure of impurity gases and hydrogen. Additionally, minimizing the influence of impurity gases on the contact zone increases the interface area between NiAl and AlMg6.

In this study, SHS was used to produce metal-intermetallic-ceramic laminate AlMg6-NiAl-TiC composite. The experiment conducted without a cylindrical powder pellet holder produced no joint between the NiAl and AlMg6 sheet. On the other hand, the experiment conducted inside a cylindrical powder pellet holder (CPPH) with a blind hole produced a joint. It was found that the AlMg6 sheet had a temperature of 400–550 °C across its entire thickness during SHS. The study of the microstructure and energy-dispersive analysis (EDS) of AlMg6-NiAl-TiC composite showed that it had five layers: (1) ceramic layer of 7-mm-thick TiC; (2) the upper diffusion layer that formed at the interface between NiAl and TiC consisted of TiC + NiAl; (3) an intermetallic layer, which consisted of 13-mm-thick NiAl; (4) the lower diffusion layer, which formed at the interface between NiAl and AlMg6; and (5) a layer of 4-mm-thick aluminum alloy AlMg6. The EDS showed that during the synthesis of NiAl and its interaction with the surface of the AlMg6 sheet, mixing of the components of the initial materials (NiAl, AlMg6) in the joint interface occurs. At the interface of NiAl and AlMg6, the microhardness was 790–870 HV, which indicates the presence of quenching structures in the melted zones. [ABSTRACT FROM AUTHOR]

NiAl-based intermetallic coatings were obtained using non-vacuum electron beam cladding on low-carbon steel. The structure of the coatings was investigated using optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD). The coatings mostly consisted of grains elongated perpendicular to the substrates, with a strong <100> texture along the grain growth direction. The coatings contained about 14 at. % Fe, which appeared due to the partial melting of the steel substrate. At the bottom of the coatings, an inhomogeneous mixing zone with an increased concentration of Fe was formed; at the "substrate–coating" interface, a thick layer with a Fe50-Ni25-Al25 at. % composition was observed. The samples exhibited weight gains of 0.1, 0.8, 2.14, and 3.4 mg/cm2 after 100 h of oxidation at 700, 800, 900, and 1000 °C, respectively. The oxide layer contained α-Al2O3 and θ-Al2O3, and the presence of iron atoms contributed to the formation of a small amount of spinel. During the oxidation process, a layer with a high Fe content (~60 at. %) formed along the boundary between the oxide film and the NiAl-based material, which had a positive effect on the formation of a non-porous "oxide–coating" interface. [ABSTRACT FROM AUTHOR]

This paper presents the implementation of the first stage of a study on the synthesis of the intermetallic compound in the Ni-Al system under shock-wave extrusion (SWE). A method was developed and experiments involving SWE of the reactive Ni–Al powder mixture were carried out. As a result, it was possible to obtain up to 56 vol.% of the final product and achieve 100% synthesis of NiAl. The results of metallographic analysis indicate that the process of high-velocity collapse of the tube created conditions for the formation of a cumulative flow, which directly affects the phase formation in NiAl. It was shown that the presence of the central hole in the powder sample reduced the effect of the Mach stem on the homogeneity of the NiAl structure. It was also determined that with a central hole with a 5 mm diameter, the effect of the Mach stem could not be observed at all. The goals of further studies are achieving 90–100 vol.% of the final product and reducing the porosity in the final product. Preliminary experimental studies have shown great potential for SWE to produce composite metal–intermetallic materials. [ABSTRACT FROM AUTHOR]

The scientific goal of this paper is to study and explain the relationship between the microstructure of a ceramic–intermetallic composite fabricated by consolidating a mixture of Al2O3 and NiAl-Al2O3 using the PPS technique and its basic mechanical properties. Six series of composites were manufactured. The obtained samples differed in the sintering temperature and content of compo-powder. The base powders, compo-powder, and composites were investigated using SEM equipped with an EDS and XRD. Hardness tests and KIC measurements were applied to estimate the mechanical properties of the fabricated composites. The wear resistance was evaluated using a “ball-on-disc” method. The results demonstrate that the density of the obtained composites increases with the increased temperature of the sintering. The content of NiAl + 20 wt.% Al2O3 did not have a determining effect on the hardness of the manufactured composites. The highest hardness, contacting 20.9 ± 0.8 GPa, was found for the composite series sintered at 1300 °C and 2.5 vol.% of compo-powder. The highest KIC value from all the studied series equaled 8.13 ± 0.55 MPa·m0.5 and was also achieved for the series manufactured at 1300 °C (2.5 vol.% of compo-powder). The average friction coefficient during the ball-friction test with the Si3N4 ceramic counter-sample was between 0.8 and 0.95.

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Coatings were obtained by vacuum electro-spark alloying (VESA), pulsed cathodic arc evaporation (PCAE), magnetron sputtering (MS) techniques and VESA-PCAE-MS hybrid technology using Cr 3 C 2 –NiAl electrodes. The structure of the coatings was analyzed using scanning and transmission electron microscopy, X-ray diffraction and energy-dispersive spectroscopy. Mechanical properties were determined by nanoindentation, while tribological properties were assessed using pin-on-disk tribometer. Corrosion resistance was estimated by voltammetry in 1 N H 2 SO 4 and 3.5%NaCl solutions. Oxidation resistance tests were performed at 800°С in air. The VESA coating had the highest thickness, low friction coefficient and high wear resistance. PCAE coating demonstrated the highest hardness (24 GPa) and elastic recovery (59%), oxidation resistance and superior corrosion resistance both in 1 N H 2 SO 4 (i corr = 70 μА/cm2) and 3.5%NaCl (i corr = 0.74 μА/cm2) solutions. The MS coating had average mechanical properties and low corrosion current density (71 μА/cm2) in 1 N H 2 SO 4. Deposition of coatings using VESA-PCAE-MS hybrid technology led to an increase in corrosion and oxidation resistance at least by 1.5 times in comparison with the VESA coating. [ABSTRACT FROM AUTHOR]

Water vapor is ubiquitously present for energy conversion and combustion systems, yet its effect on the oxidation of crucial structure components of heat-resistant alloys remains elusive. Departure from the well-established phenomenon of exclusive alumina growth from the NiAl oxidation in dry O 2 , we demonstrate that the NiAl oxidation in H 2 O results in the precipitation of a significant number of metallic Ni clusters within the Al 2 O 3 scale by adsorbing Ni atoms from the alloy through a vacancy-assisted solute capture solute capture process of the enhanced oxide/alloy interface migration. The Ni clusters initially have a hcp structure at small sized, transitioning into an fcc structure when their size exceeds ∼12.5 nm. Using atomistic modeling, we show that the dissolution of a high concentration of H derived from H 2 O into the oxide scale is the key to stabilizing the hcp Ni structure. Subsequent coarsening of the hcp Ni clusters lowers the H concentration, leading to the hcp → fcc transformation. These results provide mechanistic insight into the effect of water vapor on the long-term stability of the structure alloys by influencing the oxidation-induced mass transport across the scale/alloy interface and microstructure evolution within the oxide scale. • NiAl oxidation in H 2 O results in the precipitation of metallic Ni clusters in the Al 2 O 3 scale. • The Ni clusters initially have the hcp structure at the small size and transform into the fcc structure at the size greater than ∼12.5 nm. • A high concentration of H derived from H 2 O into the oxide scale is the key to stabilizing the hcp Ni structure. • The coarsening of hcp Ni clusters lowers the H concentration and thus results in the hcp to fcc transformation. [ABSTRACT FROM AUTHOR]

In recent times, high temperature operated coatings are becoming popular as they offer protection against both elevated as well as harsh environment to improve wear performance. Herein, we investigated and demonstrated an in-situ high-temperature wear behaviour over nanodiamond reinforced nickel-aluminium composite coatings up to 873K. The composite coating offered a substantial reduction in wear rate and COF up to 873K. At 873K, wear rate reduced by 97.3%, and COF dropped by 95.24% over ND reinforced NiAl composite coating comparing it with NiAl coating. Further, the findings were attributed with the help of lubricating effect of ND, formation of protective carbide and oxide etc. layers. This impressive research can pave the way for effective protection of the components up to elevated temperatures (873K). • Study of wear properties from RT to 873K. • NA1D composite coating showed 95.2% reduction in COF. • Addition of 1 wt% NDs reduced the wear rate by 97.3%. • Enhanced wear properties attributed to formation tribofilm. [ABSTRACT FROM AUTHOR]

In this work, the intermetallic matrix composite coatings of the TiC-Ti2Ni-Ti3Al system were investigated. Induction heating was used to initiate the self-propagation high-temperature synthesis (SHS) reaction of the multilayer systems of Ti/C-Ni/Al-Ti on the steel substrate. The role of Ni/Al reaction on the SHS process of Ti/C-Ni/Al-Ti was compared to that of Ni/Al-Ti. The results showed that the TiC composite system was composed of TiC dispersed in the intermetallic Ti-Al and Ti-Al systems. This indicates that high exothermic reaction of the SHS process of Ni/Al initiated the subsequent reactions in the Ti-Al, Ti-Ni, and Ti-C systems. The Ti3Al-Ti2Ni multiphase system was formed due to the interaction between the liquid product of NiAl and Ti. Surprisingly, NiAl was disappeared in the Ti/C-Ni/Al-Ti system. This work improves the understanding of the formation mechanism of the NiAl reaction as the agent for the formation of TiC-Ti2Ni-Ti3Al intermetallic matrix composite. [ABSTRACT FROM AUTHOR]

We present the elastic constants of NiAl and FeAl compounds under high pressure and high temperature by using a first-principles approach. The temperature dependent elastic constants are predicted from the combinations of static volume-dependent elastic constants derived from the first principles total-energy method within the density-functional theory (DFT). The calculated lattice and elastic constants at ground state are in agreement with the existing experimental and other theoretical values. Using the density-functional perturbation theory (DFPT) under the quasi-harmonic approximation (QHA), the temperature and pressure dependencies of the bulk modulus, the volume expansion, the thermal expansion, as well as the heat capacity at constant pressure are systematically investigated in the ranges of 0–1200 K and 0–50 GPa. [ABSTRACT FROM AUTHOR]

We performed high-temperature treatment of the Ni–C, Al–C, and Ni–Al–C powder mixtures (5 wt % C (soot)) up to the melting point of the respective metals and found that the melt particles coagulate with formation of Ni, Al, and NiAl (intermetallic) spherical particles, respectively. The Ni particles have almost perfect spherical shape and a multilayer graphite coating. The NiAl particles have a thin graphene (graphite) coating. [ABSTRACT FROM AUTHOR]

High temperature oxidation resistant aluminide coatings fail due to their inability to maintain a protective scale. The corresponding mechanism of protection is based on of forming a thin Al2O3 layer, which depends on the availability of Al at the interface with the intermetallic coating. However, the Al content in the coating’s surface decreases with time at high temperatures due to interdiffusion with the substrate and/or frequent regeneration of the protective Al2O3 scale when it spalls. Si addition is known to enhance the life of Ni aluminide coatings under certain corrosion environments. In an effort to develop a stable, long lasting coating for industrial components exposed to metal dusting, diffusion aluminide coating has been produced by applying Al-Si slurries of various compositions on alloy 601. Aluminide coatings were prepared by applying a water base, Al slurry to which 1, 10 and 20 wt. % of Si were added, followed by a diffusion heat treatment. The microstructures of the coatings were similar, exhibiting an outer layer consisting of an Al-rich β-NiAl matrix, an almost stoichiometric β-NiAl inner layer and an interdiffusion zone between the coating and the alloy. Thermal cyclic tests in air at 1100 °C have demonstrated good adhesion and stability of all coatings. In addition, long term isothermal tests at 850 °C for up to 3 months in air showed high oxidation resistance of the coating but different degree of coating degradation depending on the composition. The coating with the lowest Si addition was the most stable.

Metal-bonded diamond tools are widely used for machining hard and brittle materials such as ceramic and stone. The metal bonds are normally based on alloys composed of Fe, Co, Ni, Cu, Sn, Zn, or Cr. However, high heavy metal concentrations are hazardous to the environment and tool operators. Furthermore, the high density of these metal bonds results in excessively heavy tools, requiring high energy and intensive labor during operation. Therefore, we propose two environmentally friendly and lightweight metal bonds based on NiAl and FeAl intermetallics for diamond tools by reactive hot-press sintering. The effect of sintering temperature on the microstructure and mechanical properties of NiAl and FeAl was examined and the tribological behavior of NiAl and FeAl on Si 3 N 4 ceramic balls was investigated. Grinding performance of the sintered diamond tools on Si 3 N 4 ceramic was also compared. Our results reveal that B2-ordered NiAl and FeAl are obtained at sintering temperatures in the range of 700–1100 °C. The relative density of sintered NiAl is higher than that of FeAl, while the Vickers hardness and flexural strength of NiAl are lower than that of FeAl. Compared with FeAl, NiAl demonstrates higher wear resistance in a friction test against Si 3 N 4 ceramic, while FeAl-bonded diamond tools demonstrate a higher grinding ratio than NiAl-bonded diamond tools due to enhanced self-sharpening ability. Nevertheless, diamond tools based on both NiAl and FeAl can be used to grind Si 3 N 4 ceramics. [ABSTRACT FROM AUTHOR]

Using the Cr3C2–NiAl cathode prepared by self-propagating high-temperature synthesis, Cr‒Ni–Al–C–N coatings are deposited by pulsed cathode arc evaporation in argon, nitrogen, and ethylene atmospheres. The coating structures are investigated by scanning electron microscopy, X-ray diffraction analysis, glow-discharge optical emission spectroscopy, and Raman spectroscopy. Mechanical and tribological properties are investigated by nanoindentation and pin-on-disk tribological testing. Anticorrosion properties are evaluated by voltammetry in the medium of a 1-N H2SO4 solution. The nonreactive coating deposited in an inert Ar atmosphere contains the Cr3C2 fcc phase with a size of crystallites below 20 nm. The deposition in the C2H4 and N2 reaction media leads to amorphization of the coatings. The samples deposited in argon and nitrogen exhibit high hardness values of 24–25 GPa. The deposition of coatings in C2H4 gives rise to a 40% decrease in the hardness. However, the carbon-containing sample has a relatively low coefficient of friction at a level of 0.28, as well as better wear and corrosion resistances due to the positive effect of the diamond-like carbon phase. [ABSTRACT FROM AUTHOR]

Анализ атомной и фазовой структуры подтвердил различие структурно-фазовых состояний на этапах нагрева и охлаждения. На основе анализа влияния отклонения атомного состава от стехиометрического на состояния интерметаллида в процессе охлаждения установлено, что отклонение оказывается существенным фактором в области предпереходных слабоустойчивых структурно-фазовых состояний перед превращением. Поведение кривых температурных зависимостей параметра дальнего порядка при охлаждении сплавов нестехиометрических составов существенно отличаются от поведения соответствующей кривой сплава стехиометрического состава. Показано, что в случае охлаждения сплавов нестехиометрических составов для установления дальнего порядка требуется существенное переохлаждение, а появление упорядоченных фаз происходит при значительно более низких температурах. Установлено, что кривая температурной зависимости параметра дальнего порядка сплава Ni45Al55 лежит существенно ниже соответствующей кривой сплава Ni55Al45. Это свидетельствует о разных механизмах установления дальнего порядка сплавов с нестехиометрическими составами. Отмечено, что отклонение состава системы от стехиометрического вызывает существенное измельчение упорядоченных и неупорядоченных областей. Данная статья является продолжением работы, опубликованной ранее в журнале Известия АлтГУ. 2020. №1 (111).

Результаты работы представлены в виде двух частей. В первой части приведены данные, описывающие общее состояние проблемы проявления слабоустойчивых структурно-фазовых состояний в интерметаллидах в системе Ni-Al. Описаны физические представления о слабоустойчивых структурнофазовых состояниях в конденсированных системах и применяемая физико-математическая модель, в основе которой лежит расчетный блок из 32x32x32 элементарных ячеек (65536 атомов) упорядоченной ОЦК-структуры (сверхструктура B2, символ Пирсона сР2). Исследование проведено в рамках метода Монте-Карло с использованием алгоритма Метрополиса на примере интерметаллида NiAl стехиометрического состава. Установлено, что при термоциклировании наблюдается своеобразный гистерезис, наличие которого свидетельствует о необратимости происходящих процессов, что подразумевает различие структурно-фазовых состояний на этапах нагрева и охлаждения. Во второй части будут представлены результаты компьютерного моделирования изменения структурно-фазовых состояний с особым вниманием на слабоустойчивые предпереходные состояния и энергетические характеристики интер-металлидов с отклонениями от стехиометрического состава Ni45Al55 и Ni55Al45.

In this study, SHS was used to produce metal-intermetallic-ceramic laminate AlMg6-NiAl-TiC composite. The experiment conducted without a cylindrical powder pellet holder produced no joint between the NiAl and AlMg6 sheet. On the other hand, the experiment conducted inside a cylindrical powder pellet holder (CPPH) with a blind hole produced a joint. It was found that the AlMg6 sheet had a temperature of 400–550 °C across its entire thickness during SHS. The study of the microstructure and energy-dispersive analysis (EDS) of AlMg6-NiAl-TiC composite showed that it had five layers: (1) ceramic layer of 7-mm-thick TiC; (2) the upper diffusion layer that formed at the interface between NiAl and TiC consisted of TiC + NiAl; (3) an intermetallic layer, which consisted of 13-mm-thick NiAl; (4) the lower diffusion layer, which formed at the interface between NiAl and AlMg6; and (5) a layer of 4-mm-thick aluminum alloy AlMg6. The EDS showed that during the synthesis of NiAl and its interaction with the surface of the AlMg6 sheet, mixing of the components of the initial materials (NiAl, AlMg6) in the joint interface occurs. At the interface of NiAl and AlMg6, the microhardness was 790–870 HV, which indicates the presence of quenching structures in the melted zones.

NiAl-based intermetallic coatings were obtained using non-vacuum electron beam cladding on low-carbon steel. The structure of the coatings was investigated using optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD). The coatings mostly consisted of grains elongated perpendicular to the substrates, with a strong texture along the grain growth direction. The coatings contained about 14 at. % Fe, which appeared due to the partial melting of the steel substrate. At the bottom of the coatings, an inhomogeneous mixing zone with an increased concentration of Fe was formed; at the “substrate–coating” interface, a thick layer with a Fe50-Ni25-Al25 at. % composition was observed. The samples exhibited weight gains of 0.1, 0.8, 2.14, and 3.4 mg/cm2 after 100 h of oxidation at 700, 800, 900, and 1000 °C, respectively. The oxide layer contained α-Al2O3 and θ-Al2O3, and the presence of iron atoms contributed to the formation of a small amount of spinel. During the oxidation process, a layer with a high Fe content (~60 at. %) formed along the boundary between the oxide film and the NiAl-based material, which had a positive effect on the formation of a non-porous “oxide–coating” interface.

This paper presents the implementation of the first stage of a study on the synthesis of the intermetallic compound in the Ni-Al system under shock-wave extrusion (SWE). A method was developed and experiments involving SWE of the reactive Ni–Al powder mixture were carried out. As a result, it was possible to obtain up to 56 vol.% of the final product and achieve 100% synthesis of NiAl. The results of metallographic analysis indicate that the process of high-velocity collapse of the tube created conditions for the formation of a cumulative flow, which directly affects the phase formation in NiAl. It was shown that the presence of the central hole in the powder sample reduced the effect of the Mach stem on the homogeneity of the NiAl structure. It was also determined that with a central hole with a 5 mm diameter, the effect of the Mach stem could not be observed at all. The goals of further studies are achieving 90–100 vol.% of the final product and reducing the porosity in the final product. Preliminary experimental studies have shown great potential for SWE to produce composite metal–intermetallic materials.

The oxidation behaviour of Ni8Al and Ni25Cr coatings produced by high velocity oxygen fuel spray (HVOF) which were deposited on Fe-based alloys (CB2) was investigated. We simulated the service environment of the steam generator unit, and put the samples in a thermostatic tube furnace at 650 ∘ in air with 20 wt.% water vapor for 1000 hours of cyclic oxidation. The formation mechanism are explained using SEM, XRD, and EDX. There were no spallations and obvious cracks in both coatings. Ni25Cr coating generated a better protection oxides scale than that scale on Ni8Al. The behavior and mechanism of the oxide scale formation had an important influence in coatings and we have discussed these phenomenons in the study. [ABSTRACT FROM AUTHOR]

The transient stage of alumina scale formation on alumina-forming alloys is often accompanied by the formation of metastable Al2O3 phases that may affect oxidation kinetics and scale microstructure. To clarify the role of dopants on the transient stage of NiAl oxidation, we characterized Al2O3 scales on a series of oxidized model β-NiAl samples that were un-doped or doped with additions of Ti, Y, Si, Ti + Y, and Si + Y. Our results confirm that different dopant elements (Ti, Si, and Y) have varied effects on the length of transient oxidation of alumina-forming alloys. Ti and Si accelerated the θ- to α-Al2O3 transformation via two different mechanisms. Ti promoted α-Al2O3 nucleation, while Si delayed nucleation but accelerated the lateral growth of the α-Al2O3 patches. In contrast, Y had little effect on alumina transformation, possibly due to the low Y concentration used in the current study. [ABSTRACT FROM AUTHOR]

The high-temperature oxidation of the NiAl alloy in the CO 2 and O 2 atmospheres is comparatively studied by a combination of electron microscopy characterization and first-principles calculations. It is shown that CO 2 accelerates the oxidation of NiAl alloy by the formation of a highly porous γ-Al 2 O 3 scale that is non-protective and follows the linear growth law. By contrast, the NiAl oxidation in O 2 results in a double-layered oxide scale consisting of an outer columnar γ-Al 2 O 3 layer and an inner equiaxed α-Al 2 O 3 layer, which is protective and follows parabolic growth law. Our first-principles calculations show that this accelerated NiAl oxidation in the CO 2 can be attributed to more ready decomposition of adsorbed CO 2 than adsorbed O 2 into atomic oxygen on defective γ-Al 2 O 3 surfaces, which leads to the inward γ-Al 2 O 3 growth by the infiltration of gaseous CO 2 through the cracked oxide scale toward the exposed NiAl alloy. These results provide new insights into the atomic origin of CO 2 -promoted alloy oxidation. • CO 2 accelerates the oxidation of NiAl alloy compared with O 2. • The oxidation of NiAl alloy in the CO 2 results in a highly porous γ-Al 2 O 3 scale. • CO 2 is more readily to decompose than O 2 on the defective γ-Al 2 O 3 surface. • The rapid decomposition of CO 2 creates atomic O for the fast oxide growth. • The defective oxide allows the infiltration of gaseous CO 2 for inward γ-Al 2 O 3 growth. [ABSTRACT FROM AUTHOR]

Development of new ultrahigh strength steels with high strength and high toughness requires thorough comprehension of nanoscale precipitation mechanisms. In this investigation, a comprehensive array of techniques including atom probe tomography, transmission electron microscopy, scanning electron microscopy, electron backscatter diffraction, small angle x-ray Scattering and thermodynamic calculations were employed. These methods unveiled an intriguing co-precipitation mechanism involving NiAl and carbide nanoparticles in a 2.2 GPa grade strength steel. The results demonstrate that the precipitation mechanisms of NiAl and carbides at different aging temperatures have a significant impact on the strength and toughness of the steel. Sub-micron ε-carbide at the interface of martensite lath and uniformly distributed NiAl cluster in the matrix are independent nucleation during the low-temperature aging process. The high distribution density of NiAl cluster in the matrix results in an increase in the impact absorbed energy of the steel to 136 J, albeit with a slight decrease in strength. On the other hand, the NiAl with minimal lattice misfit and low interfacial energy preferentially nucleates uniformly in the matrix, inducing the nucleation of M 2 C and increasing the number density of M 2 C precipitates at the secondary hardening temperature. The homogeneous precipitation of spherical NiAl, along with needle-shaped M 2 C in the martensite, significantly enhances the strength of the steel, with a tensile strength reaching up to 2216 MPa and an impact absorbed energy of 21 J. • Ultra-high-strength steel with an excellent combination of strength (above 2.2 GPa) and ductility (approaching 12%) was achieved through a new dual-precipitates design concept with controlled dual precipitation of nanoscale NiAl and M 2 C phases. • Sub-micron ε-carbide at the interface of martensite lath and uniformly distributed NiAl cluster in the matrix are independent nucleation during the low-temperature aging process. The high distribution density of NiAl cluster in the matrix results in an increase in the impact absorbed energy of the steel to 136 J • The staged precipitation characteristics between the dual-precipitation co-configuration under different aging temperature were first revealed by 3D-APT, HR-TEM and SAXS characterization. [ABSTRACT FROM AUTHOR]

Crystal structure and composition are inter-dependent and decoupling their effects on surface reactivity is challenging. Using low-energy electron microscopy to spatially and temporally resolve the oxide film growth during the oxidation of NiAl(100), we differentiate such coupled effects by monitoring oxide growth while simultaneously fine-tuning the surface structure and composition during oxidation. We demonstrate that the oxidation of chemically ordered surfaces results in compact oxide island growth whereas non-compact oxide growth during the surface phase transition. By incorporating the surface phase transition induced chemical disordering into kinetic Monte Carlo simulations, we show that the non-compact oxide growth is induced by the composition effect on the surface diffusion of oxygen, which can be described by the concept of "ant in the labyrinth". Image, graphical abstract [ABSTRACT FROM AUTHOR]

Endogenetic particles TiB2 (5 and 10 vol.-%)-reinforced NiAl matrix composites were fabricated in-situ from Ti–B–Ni–Al system by arc melting. The oxidation behaviour and anti-oxidant mechanism of TiB2–NiAl composite were investigated at 1173 K in air atmosphere. The composite had a rapid rate of oxidation during the first 20 h. With the increase in oxidation time, α-Al2O3 oxidation films and needle-shaped TiO2 phases were formed on the surface of the composite. As the Al oxidised into Al2O3, the NiAl phase transformed into γ-Ni3Al phase. The oxides were beneficial for improving the oxidation resistance of the composite. The mass change of the composite was less than 2.5 mg cm−2 after being oxidised at 1173 K in air atmosphere for 100 h. The composite showed excellent high-temperature oxidation resistance. [ABSTRACT FROM AUTHOR]

NiAl–TiC–TiB 2 intermetallic matrix composite coatings with various TiC–TiB 2 contents were fabricated by depositing self-propagating high-temperature synthesized (SHS) NiAl–TiC–TiB 2 powders using atmospheric plasma spraying (APS) technique. The preparation process was carefully investigated and the effects of TiC–TiB 2 contents on the physical and chemical properties of the composite coating were studied. Results indicate that SHS synthesized NiAl–TiC–TiB 2 intermetallic matrix materials show high purity. The TiC–TiB 2 particles are well dispersed in the NiAl matrix. There is no obvious oxidation in the composite coating during the APS process. With an increase in TiC–TiB 2 contents, the hardness of NiAl–TiC–TiB 2 composite coating is increased, while the thermal expansion coefficient (TEC) of the coating is decreased. NiAl–TiC–TiB 2 intermetallic matrix composite coating with moderate TiC–TiB 2 content shows the best corrosion resistance. Few TiC–TiB 2 particles in NiAl promote the formation of the continuous Al 2 O 3 film without destroying the integrity of the film improving the corrosion resistance of the coating. [ABSTRACT FROM AUTHOR]

Boron carbide is a useful material due to its attractive properties, but its applications are limited due to difficulties associated with its processing. This paper presents the results of experimental studies carried out on densification, microstructural characterization and property evolution of B4C-NiAl composite. Densification studies revealed that NiAl addition to B4C results in its densification at a lower hot pressing temperature of 1700 °C at a pressure of 35 MPa. The enhancement in the densification is attributed to liquid-phase sintering caused by the presence of liquid NiAl at 1700 °C. Microstructural characterization revealed that B4C and NiAl phases are compatible with each other. NiAl addition has been found to decrease the hardness and increase the fracture toughness. B4C-NiAl composite was found to have good oxidation resistance at 900 °C in air. Tribology studies have shown that B4C-NiAl composite has good wear resistance against WC ball. [ABSTRACT FROM AUTHOR]

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The NiAl–Cr–Co–X alloys were produced by centrifugal self-propagating high-temperature synthesis (SHS) casting. The effects of dopants X = La, Mo, Zr, Ta, and Re on combustion, as well as the phase composition, structure, and properties of the resulting cast alloys, have been studied. The greatest improvement in overall properties was achieved when the alloys were co-doped with 15% Mo and 1.5% Re. By forming a ductile matrix, molybdenum enhanced strength characteristics up to the values σucs = 1604 ± 80 MPa, σys = 1520 ± 80 MPa, and εpd = 0.79%, while annealing at T = 1250 ℃ and t = 180 min improved strength characteristics to the following level: σucs = 1800 ± 80 MPa, σys = 1670 ± 80 MPa, and εpd = 1.58%. Rhenium modified the structure of the alloy and further improved its properties. The mechanical properties of the NiAl, ZrNi5, Ni0.92Ta0.08, (Al,Ta)Ni3, and Al(Re,Ni)3 phases were determined by nanoindentation. The three-level hierarchical structure of the NiAl–Cr–Co+15%Mo alloy was identified. The optimal plasma treatment regime was identified, and narrow-fraction powders (fraction 8–27 µm) characterized by 95% degree of spheroidization and the content of nanosized fraction