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The influence of oxidizing atmosphere on the degradation mechanisms of the Ni-based superalloy Rene 65 was studied in this work. Oxidation was carried out in synthetic air, argon and water vapor (Ar + 18 vol.%H2O) between 700 and 900 °C, with samples built following additive manufacturing and forging processing routes. The results showed that the processing route and hence, the derived microstructure did not significantly affect the oxidation behavior. In contrast, the oxidizing atmosphere markedly modified the oxidation kinetics, the growth of the oxide layers and the overall oxidation mechanisms. The resulting thin oxide scales were made of NiCr2O4 and Cr2O3 at 700 °C, while at 800 and 900 °C the oxide layer was composed of an external Cr2O3 layer on top of an internal α-Al2O3 layer resulting from the lower partial pressure of oxygen underneath the chromia layer. The presence of nitrogen in the synthetic air favored the internal formation of TiN, while the absence of nitrogen in argon revealed the doping effect of Ti on the formation of the Cr2O3 layer. The effect of water vapor in Ar was not significant as the oxidation behavior was close to that observed under argon. [ABSTRACT FROM AUTHOR]

Fatigue tests of nickel-based single-crystal superalloys with inclined film cooling holes (FCHs) at 1000°C were conducted to investigate the effects of crystal orientation and to quantify the fatigue performance of the high-temperature structures. Fractographic analysis and computations of stress concentrations revealed competitive failure mechanisms between mode I crack nucleation and fatigue crack growth in crystallographic plastic slip systems, whereas crack nucleation around inclined FCHs can be characterized by the known fatigue criteria derived for smooth specimens. A life prediction model based on the crystal slip mechanism and the theory of critical distance was introduced to predict the fatigue life of FCH structures and provided reasonable accuracy for different FCH specimens. [ABSTRACT FROM AUTHOR]

With the global energy transition and increasing environmental requirements, hydrogen-mixed gas turbines as a high-efficiency and low-emission energy conversion equipment has been widely concerned. This paper reviews the development status of hydrogen-mixed gas turbines domestically and internationally, analyzes the characteristics of hydrogen combustion in gas turbines, explores the impact of hydrogen combustion on complex components and the application of high-temperature materials, and analyzes the performance requirements for hot-end component materials operating under high temperature, high pressure, and corrosive conditions, as well as the main challenges and potential solutions in current material development. The effects of water vapor and hydrogen embrittlement during hydrogen combustion on gas turbine alloys and thermal barrier coatings are discussed in detail. Water vapor accelerates the oxidation and corrosion of alloys, leading to a decline in mechanical properties. Furthermore, hydrogen embrittlement significantly affects the toughness and durability of alloys, increasing the risk of crack propagation and fracture. In terms of the problems, future research should focus on multi-field coupling simulations and accelerated corrosion tests, considering the factors such as temperature, pressure, and different atmospheres to establish realistic environment simulators to evaluate alloy and coating performances. Additionally, the combined effects of hydrogen and water vapor on high-temperature alloys and thermal barrier coatings should be emphasized. This includes investigating the diffusion mechanisms of hydrogen in alloys, interactions with lattice defects, and the microscopic processes leading to hydrogen embrittlement. Building oxidation models in high-temperature water vapor environments, clarifying the dissociation and adsorption mechanisms of water vapor at high temperatures, the hydroxylation of protective oxide films Al2O3 and Cr2O3, and the growth behavior of non-protective oxides(e.g., spinel) are also essential. [ABSTRACT FROM AUTHOR]

This paper presents a method for obtaining cobalt(II) perrhenate from waste derived from two types of materials, i.e., Li-ion battery scrap, or more precisely, battery mass, and superalloy scrap. Both of the above-mentioned materials are a source of Co. However, a source of rhenium is perrhenic acid produced from ammonium perrhenate (recycled) by the ion exchange method using resins. Co(OH)2 can be precipitated from solutions resulting from the leaching of Li-ion battery mass, sludge from the Zn-Pb industry and superalloy scrap. The compound, after proper purification, can be used in a reaction with perrhenic acid to form Co(ReO4)2. The reaction should be conducted under the following conditions: time 1 h, room temperature, 30% excess of cobalt(II) hydroxide, and rhenium concentration in HReO4 from about 20 g/dm3 to 300 g/dm3. This work shows that with the use of Co(OH)2, obtained from waste, an anhydrous form of cobalt(II) perrhenate can be obtained, containing < 1000 ppm of the cumulative metal impurities. [ABSTRACT FROM AUTHOR]

To meet the service conditions and strength requirements of turbine stator blades and the inner and outer rings of aero engine casings, CoFeNiCrMn high-entropy alloy filler was used to braze SiCf/SiC/GH536 joints. This study investigated the effects of holding time on the joints' microstructure and mechanical properties. Key phases identified in the welded joints include MoNiSi, FCC, and Cr23C6 near the composites, with brittle Ni3Si and Fe2Si intermetallic compounds forming due to filler diffusion. Optimal brazing parameters were found to be 1220 °C for 30 min with a shear strength of 64.28 MPa. The study also highlighted that increased holding time at the same temperature enhances diffusion at the joint, increasing brittle intermetallic compounds, initially improving shear strength, which then declines. Microstructural and fracture morphology analyses revealed that insufficient insulation time leads to poor welding and stress concentration at pores, causing cracks. Excessive insulation time results in joint fractures due to the brittleness of Ni3Si and Fe2Si intermetallic. Thus, joint shear strength correlates with welding quality and intermetallic compound distribution.

Purpose – This paper is supposed to provide a critical review of current research progress on thermal management in grinding of superalloys, and future directions and challenges. By understanding the current progress and identifying the developing directions, thermal management can be achieved in the grinding of superalloys to significantly improve the grinding quality and efficiency. Design/methodology/approach – The relevant literature is collected from Web of Science, Scopus, CNKI, Google scholar, etc. A total of 185 literature is analyzed, and the findings in the literature are systematically summarized. In this case, the current development and future trends of thermal management in grinding of superalloys can be concluded. Findings – The recent developments in grinding superalloys, demands, challenges and solutions are analyzed. The theoretical basis of thermal management in grinding, the grinding heat partition analysis, is also summarized. The novel methods and technologies for thermal management are developed and reviewed, i.e. new grinding technologies and parameter optimization, super abrasive grinding wheel technologies, improved lubrication, highly efficient coolant delivery and enhanced heat transfer by passive thermal devices. Finally, the future trends and challenges are identified. Originality/value – Superalloys have excellent physical and mechanical properties, e.g. high thermal stability, and good high-temperature strength. The superalloys have been broadly applied in the aerospace, energy and automobile industries. Grinding is one of the most important precision machining technologies for superalloy parts. Owing to the mechanical and physical properties of superalloys, during grinding processes, forces are large and a massive heat is generated. Consequently, the improvement of grinding quality and efficiency is limited. It is important to conduct thermal management in the grinding of superalloys to decrease grinding forces and heat generation. The grinding heat is also dissipated in time by enhanced heat transfer methods. Therefore, it is necessary and valuable to holistically review the current situation of thermal management in grinding of superalloys and also provide the development trends and challenges.

This study outlines findings from an investigation into the development of a hydrometallurgical process for manufacturing various forms of zinc perrhenate, entirely from waste from recycling and from the Zn–Pb industry. Scraps of Re-bearing Ni-based superalloys and acidic waste, circulating zinc solutions generated during the production of Zn by the electrolytic method and which contain >45 g/dm3 of Zn, Na, Mn, and Mg, were used in the research. In the publication, the conditions for the production of three types of zinc perrhenate, i.e., Zn(ReO4)2·4H2O, Zn(ReO4)2, and Zn(ReO4)2·2H2O, are presented. As a result of the analysis of the obtained results, it was concluded that to obtain the above-mentioned forms of zinc perrhenate, zinc carbonate can be used, precipitated from acidic, waste, and multi-component solutions after their prior neutralization to pH 4.0 and partial purification from Mn, Mg, and Na using metallurgical zinc oxide. Zinc carbonate should be precipitated using Na2CO3 at pH 6.3 and subsequently purified from other impurities, i.e., Mg, Na, and Mn, using aqueous ammonia solutions. As a result, zinc carbonate was obtained, which was used in a reaction with an aqueous solution of HReO4 to produce zinc perrhenate. The precipitated forms of Zn(ReO4)2 were obtained by appropriately drying the crude and hydrated Zn(ReO4)2 to obtain its tetrahydrate, dihydrate, and anhydrous forms, respectively, using drying temperatures of 55, 135, and 185 °C. The developed technology has been submitted for a patent and is an example of a technology founded on the principles of sustainable development, with a particular emphasis on the minimalization of loss of rhenium and zinc at all stages of its realization. [ABSTRACT FROM AUTHOR]

The process of high-temperature oxidation of multicomponent multiphase HP40NbTi alloy at 1150°C with duration of up to 500 hours in air is studied experimentally at the micro level using SEM and x-ray mapping. It is shown that the process occurs under the influence of various interrelated mechanisms. The changes in the composition and structure of the surface multilayer scale and of the subsurface diffusion zone in the alloy after oxidation of various durations are studied consistently. It is demonstrated that after a long-term exposure, conditional equilibrium is established in the alloy subsurface area; the formation of scale and the internal oxidation deplete the diffusion zone of chromium and silicon. This is compensated by the diffusion of Cr, Ni and Fe from the bulk of the metal to the surface. The process slows down with time due to the increase in the depth of the diffusion zone and formation of a "barrier" layer of silicon oxides. [ABSTRACT FROM AUTHOR]

The cast IN 713 C alloy is extensively used in the aerospace and automobile industries. Even with improved casting methods, the inhomogeneity in the microstructure is still inevitable and causes strain localizations during cyclic loading. So far, the effect of microstructural variables on the low cycle fatigue (LCF) deformation behavior of IN 713 C alloy has rarely been studied. In this study, IN 713 C alloy is LCF tested at 650°C and 750°C for strain amplitudes of 0.35% to 0.6%. The results showed that the deformation heterogeneity resulted from carbides, γ′ precipitates, and γ–γ′ eutectics distribution, governing the LCF failure micro‐mechanisms. The principle fatigue cracks were seen to be initiated from the precipitate‐free zone and oxidized‐surface carbides. It is corroborated that the higher GNDs were observed at carbide/matrix, eutectic/matrix, γ′/matrix interfaces, and in the interdendritic areas where voids and cracks formed. The higher GNDs at these sites facilitate crack initiation and propagation. Highlights: The fatigue life of alloy IN 713 C is highly sensitive to the microstructure.Higher tendency for carbide cracking was observed at high Δε/2.Cracks are seen to be initiated in PFZ and at oxidized MC carbides.Higher GND density was observed near carbides and eutectics. [ABSTRACT FROM AUTHOR]

Fretting wear in the contact area between the aero-engine blade tenon and turbine disk mortise has an important influence on the performance of the aero-engine. In this paper, the tenon joint structure of the DZ125/FGH99 superalloy material is taken as the research object, and the finite element model of the fir-tree tenon joint structure is established. Through subroutine invocation and mesh adaptive control technology, the fretting wear problem of dissimilar material contact pairs under composite load is numerically studied. The results show that for the specific tenon joint structure and load and boundary conditions studied in this paper, the maximum wear occurs on the contact surface of the first tooth, and the surface will show different partial slip states in different load cycles. The slip region always extends from the two contact edges to the interior, and the upper side has a larger range. Wear has a significant effect on the stress distribution and stick–slip state of the contact surface. The second and third teeth have a small amount of wear and are basically in a stick state during the entire wear process. Therefore, wear has little effect on the stress distribution and the stick–slip state of the contact surface. This study reveals the coupling relationship between the fretting wear and contact state of the tenon joint structure. [ABSTRACT FROM AUTHOR]

This work investigates the impact of different heat treatments on the evolution of the microstructure, tensile properties, and residual stresses of Inconel 625 (IN625) processed by laser powder bed fusion (LPBF). Applying a heat treatment is an essential step to mitigate the high residual stresses in the components produced by LPBF and, simultaneously, to design the mechanical properties of the components. A high magnitude of residual stress can involve deformation and reduce the fatigue resistance of the components. In the current work, heat treatments performed at 600, 800, and 870 °C provided minimal modification on the dimensions of the grains but involved the formation of new phases, which increased the tensile strength. The results showed mitigation of the residual stresses at 800 and 870 °C correlated with the formation of Cr-rich M23C6 carbides and δ phases, respectively. Finally, the solution annealing at 1150 °C triggered recrystallization with the formation of sub-micrometric carbides, reducing the residual stresses. The solution annealing treatment involved an improvement of the ductility and a reduction in tensile strength. This work provides a guide to understanding the microstructure, residual stress, and mechanical properties evolution of the IN625 alloy under heat treatments. [ABSTRACT FROM AUTHOR]

This study aims to select a suitable process and composition for the fabrication of a functionally graded GH4169/K417G superalloy by laser metal deposition (LMD). A universal process parameter was optimized through an orthogonal test, and the influence of the preheated substrate temperature on the residual stress was investigated. Finally, the effects of preheating and composition on cracking and methods for controlling cracking were noted. As a result, equations for the relationship between the relative densities of samples prepared by LMD with different graded compositions and energy density coupled to laser parameters were established for the first time. Thus, an equation for the relationship between the appropriate laser power and graded composition was obtained. By preheating the substrate to higher temperatures, the maximum residual stress was gradually reduced from 753 to 362 MPa, and thus, the cracking tendency was suppressed partly. However, the decisive cracking factor was the γ/γ′ eutectic characteristic during the forming of K417G. When the terminal graded composition was designed to be 10% GH4169, the γ/γ′ eutectic phase exhibited a smaller size and lower quantity, which prevented cracking. The results of this research will help engineers select the appropriate compositions and processes to prepare dual-superalloy blisks. [ABSTRACT FROM AUTHOR]

This work presents the research results on the development of an innovative, hydrometallurgical technology for the production of manganese(II) perrhenate dihydrate from recycled waste. These wastes are scraps of Ni-based superalloys containing Re and scraps of Li–ion batteries containing Mn—specifically, solutions from the leaching of black mass. This work presents the conditions for the production of Mn(ReO4)2·2H2O. Thus, to obtain Mn(ReO4)2·2H2O, manganese(II) oxide was used, precipitated from the solutions obtained after the leaching of black mass from Li–ion batteries scrap and purified from Cu, Fe and Al (pH = 5.2). MnO2 precipitation was carried out at a temperature < 50 °C for 30 min using a stoichiometric amount of KMnO4 in the presence of H2O2. MnO2 precipitated in this way was purified using a 20% H2SO4 solution and then H2O. Purified MnO2 was then added alternately with a 30% H2O2 solution to an aqueous HReO4 solution. The reaction was conducted at room temperature for 30 min to obtain a pH of 6–7. Mn(ReO4)2·2H2O precipitated by evaporating the solution to dryness was purified by recrystallization from H2O with the addition of H2O2 at least twice. Purified Mn(ReO4)2·2H2O was dried at a temperature of 100–110 °C. Using the described procedure, Mn(ReO4)2·2H2O was obtained with a purity of >99.0%. This technology is an example of the green transformation method, taking into account the 6R principles. [ABSTRACT FROM AUTHOR]

High-throughput method of three targets magnetron sputter co-deposition was adopted to prepare (Nb–Ti)1-x-ySixCry composition spread alloy film (CSAF). Early oxidation behavior of the as-deposited alloy thin film was investigated in atmospheric conditions at 1250 °C for 10 min. A (Nb–Ti)1-x-ySixCry combinatorial material library covering (9.34–32.31) Si-(10.43–20.27) Cr (at. %) is obtained and as-deposited film was composed of amorphous phase. The oxidized film was separated into three regions having different oxidation products. The composition range for establishment of a protective scale (SiO2 and CrNbO4) and a small amount of Nb2O5 was ascertained efficiently across the entire alloy thin film.

This study reveals a novel understanding of the influence of annealing the feed powder, which alters the precipitate characteristics in the powder particles on the microstructure and mechanical properties of Haynes230 superalloy fabricated by laser powder bed fusion (LPBF) plus hot isostatic pressing (HIP) and solution treatment. Specifically, annealing Haynes230 superalloy powder at 1000°C for 1 h under vacuum resulted in the precipitation of M6C carbide instead of the typical M23C6 found in unannealed powder. The alloy fabricated by LPBF of the annealed powder plus HIP and heat treatment exhibited an increased number density of the carbide precipitates at grain boundaries, but a reduced number density of the intragranular carbide precipitates. Consequently, its ambient temperature tensile properties decreased clearly in terms of yield strength (406–383 MPa), ultimate tensile strength (936–841 MPa) and elongation to fracture (38.6% to 25%) compared to the alloy fabricated by LPBF of the as-received powder plus same post-print processing. However, the annealing of the feed powder had little effect on the tensile properties of the samples at 900°C. These findings underscore the significant impacts of feed powder microstructure on the mechanical properties of LPBF-processed superalloys.

The microstructure of high-entropy alloys with refractory elements and Al as constituents can be considered to be analogous to superalloys. These so-termed refractory high-entropy superalloys (RHSAs) can show remarkable compressive strength up to temperatures exceeding 1200 °C. Here, we examine the microstructure and properties - compressive, tensile, and fracture toughness - of a precipitation-hardened, body-centered cubic, RHSA, Al0.5Nb1.25Ta1.25TiZr, at ambient temperature (RT) to 1200 °C. Two dual-phase microstructures comprising ordered B2 (brittle) and disordered A2 (ductile) phases were produced in this alloy - one with B2 as the matrix, the other with A2 - for evaluation of the mechanical properties. Under compression, both microstructures display RT compressive strengths above 1.5 GPa and considerable ductility exceeding 40% at elevated temperatures; the alloy with the A2 matrix has ∼15% compressive ductility even at RT. However, properties are very different under tensile loading; at all temperatures, both microstructures fail predominately in an intergranular mode in the elastic regime at a fracture stress less than 200 MPa and ductility below 0.15%. The microstructure with the A2 matrix has a KIc fracture toughness of ∼15 MPa√m at RT, although at all temperatures above 800 °C, measured KIc values for both dual-phase microstructures are less than 5 MPa√m. In this study, we investigate the microstructural origin of these mechanical properties, and emphasize the importance of evaluating these alloys in tension.

This work represents a preliminary study of atmospheric plasma-sprayed (APS) Yttria-Stabilized Zirconia (YSZ)-based thermal barrier coatings (TBCs) deposited on forged and additive manufactured (AM) HAYNES®282® (H282) superalloy substrates. The effect of different feedstock morphologies and spray gun designs with radial and axial injection on APS-deposited YSZ layer characteristics such as microstructure, porosity content, roughness, etc., has been investigated. The performance of TBCs in terms of thermal cycling fatigue (TCF) lifetime and erosion behaviour were also comprehensively investigated. In view of the high surface roughness of as-built AM surfaces compared to forged substrates, two different types of NiCoCrAlY bond coats were examined: one involved high-velocity air fuel (HVAF) spraying of a finer powder, and the other involved APS deposition of a coarser feedstock. Despite the process and feedstock differences, the above two routes yielded comparable bond coat surface roughness on both types of substrates. Variation in porosity level in the APS topcoat was observed when deposited using different YSZ feedstock powders employing axial or radial injection. However, the resultant TBCs on AM-derived substrates were observed to possess similar microstructures and functional properties as TBCs deposited on reference (forged) substrates for any given YSZ deposition process and feedstock. [ABSTRACT FROM AUTHOR]

The high-temperature oxidation behavior of a novel γ′-strengthened CoNi-base superalloy was investigated by isothermal oxidation in air at 700 °C and 900 °C. The results show that the superalloy formed a multilayered oxide scale at the two temperatures, exhibiting parabolic oxidation kinetics. Theoretical calculations suggest that the alloy Al content was insufficient to form a protective alumina scale and elevating temperature was beneficial for reducing the critical Al concentrations required for alumina scale formation. In agreement with the predications, a discontinuous alumina band was developed at the oxidation front as the temperature was increased from 700 to 900 °C. [ABSTRACT FROM AUTHOR]

Recently, self-propelled rotary tools have garnered significant attention due to their potential to enhance machining productivity. The fundamental principle behind these tools involves the utilization of a circular cutting instrument that continually rotates around its axis during machining. This rotational motion facilitates a more effective distribution of thermomechanical stresses along the cutting edge. Existing literature reveals promising outcomes regarding the wear performance of these tools. However, their optimization in terms of development and parameterization remains suboptimal due to insufficient experimental data and limited analysis of thermomechanical phenomena. To comprehend the underlying phenomenology governing the operation of these tools, it is crucial to identify the relationship between the rotation speed of the insert and various cutting and engagement parameters, as well as the insert's inclination and geometry. This study relies on an experimental turning apparatus capable of non-intrusively monitoring the continuous rotation of the insert. By employing specialized image analysis techniques, the registered images of the insert during machining are examined in detail. Subsequent processing of these images, while eliminating the interference caused by disruptive chips, enables the determination of the insert's rotation speed. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) has been increasingly used for gas turbine (GT) components over the last decade. Many different components can be successfully designed, printed, and used in the gas turbine. However, there still exist questions on the use of AM components in hot-section areas. These components are typically fabricated from nickel-base superalloys that are known to have superior mechanical properties at elevated temperatures (e.g., creep and fatigue). Research over the last decade has been primarily focused on the printability of nickel-base superalloys, and there still exists a gap in understanding the high temperature processing-structure-properties-performance relationships of these alloy systems. This study evaluates the effect of processing methods, such as laser-based powder bed fusion (LBPBF) and electron beam powder bed fusion (EBPBF), on the resulting microstructure and time dependent mechanical properties of a nickel-base superalloy (ABD®900). Material after each build was subsequently heat treated using both near-solvus (at or slightly below the gamma prime solvus temperature) and super-solvus (above gamma prime solvus temperature) conditions. Multistep aging was then carried out to produce a bi-modal distribution of gamma prime precipitates as is typical in similar alloys. Microstructure was evaluated in both the as-built and fully heat-treated conditions for each processing technique. Mechanical testing was conducted to evaluate the effects of AM build methods, microstructure, and heat treatment on high temperature mechanical properties. The results show that there are several methods which can be used to improve the performance of components built using AM. The creep testing results for ABD900-AM clearly show an improvement in properties (rupture life and ductility) at all test conditions compared to testing in the prior AM alloy of the same class. A super-solvus heat treatment improved creep rupture strength by ∼3× in the LBPBF material compared to the near-solvus heat treatment. These findings provide directions for future studies to advance the overall state of gas turbine technology by enabling ABD®900-AM material and other AM alloys to be used in more innovative hot-section components. [ABSTRACT FROM AUTHOR]

This work proposes a methodology for designing high-strength precipitation-hardened high entropy alloys (HEAs) with an FCC matrix and L12 precipitates. High-throughput solidification calculations were conducted using the CALPHAD method, evaluating 11,235 alloys in the Cr-Co-Ni-Al-Ti system under specific boundary conditions. The acquired information was used to filter the alloys, focusing on alloys exhibiting an FCC+L12 phase field at 750 °C, a solidification interval narrower than 100 °C, and a solvus temperature under 1100 °C. The filtered alloys were analyzed to estimate their solid solution and precipitation hardening contributions to yield strength, with antiphase boundary energy (APB) assessed using two models. Three alloys were selected for testing the proposed strategy, including one with the highest yield stress and others for comparison. These alloys were produced, processed, and characterized using DSC, synchrotron XRD, SEM, and TEM. The results showed that the desired microstructure was achieved, with the alloys consisting of an FCC matrix and a high-volume fraction of L12 precipitates. Tensile tests at room temperature, 650 °C, 750 °C, and 850 °C demonstrated that the proposed model predicts well the yield strength trends, demonstrating the potential of the proposed approach for accelerating the discovery and development of novel HEAs with tailored properties.

Nickel-based superalloys are important structural materials in turbine engines and gas turbines，but their conventional fabrication processes are complex，costly and have poor raw-material-utilization rate. The electron beam powder bed fusion（EBPBF） technology is a new solution for forming superalloys，which can realize near net forming of complex structural parts. During more than ten years of development，EBPBF technology has realized the high-quality formation of superalloy materials and components represented by Inconel 718 and Inconel 625，and has continuously extended its capability to form crack-free，high-γ'-phase-portion difficult-to-weld nickel-based superalloys，and can even directly prepare single-crystal nickel-based superalloy components. In this paper，the relevant literatures on EBPBF nickel-based superalloys in recent years are reviewed，and the current research status from the perspectives of printability，process optimization，property characterization of EBPBF nickel based superalloy components are analyzed and summarized，and also the future research work is proposed.

This paper presents a method for obtaining cobalt(II) perrhenate from waste derived from two types of materials, i.e., Li-ion battery scrap, or more precisely, battery mass, and superalloy scrap. Both of the above-mentioned materials are a source of Co. However, a source of rhenium is perrhenic acid produced from ammonium perrhenate (recycled) by the ion exchange method using resins. Co(OH)2 can be precipitated from solutions resulting from the leaching of Li-ion battery mass, sludge from the Zn-Pb industry and superalloy scrap. The compound, after proper purification, can be used in a reaction with perrhenic acid to form Co(ReO4)2. The reaction should be conducted under the following conditions: time 1 h, room temperature, 30% excess of cobalt(II) hydroxide, and rhenium concentration in HReO4 from about 20 g/dm3 to 300 g/dm3. This work shows that with the use of Co(OH)2, obtained from waste, an anhydrous form of cobalt(II) perrhenate can be obtained, containing < 1000 ppm of the cumulative metal impurities.

The failure of transpassive films on transition metal alloys was investigated. The results show that the failure of the transpassive film on 3D printing nickel-based superalloy in flowing NaNO3 solution is dominated by self-induced cracking of the film on niobium-segregated phases and the erosion-induced degradation on the film assisted by cation vacancy condensation at the metal/barrier layer interface. Secondary passivation induces the formation of a transpassive film, the nature of which has been debated for decades. The findings are consistent with a bi-layer structure comprising a point-defective barrier layer that grows into the substrate alloy and a precipitated outer layer.

The main strengthening mechanism for Inconel 718 (IN718), a Ni-based superalloy, is precipitation hardening by γ′ and γ″ particles. It is thus essential, for good alloy performance, that precipitates with the desired chemical composition have adequate size and dispersion. The distribution of the γ′ and γ″ phases and their chemical composition were investigated in the nickel-based Inconel 718 superalloy by taking advantage of the new capabilities of scanning transmission electron microscopy and energy-dispersive X-ray spectrometry using a windowless multiple detector, a high-brightness Schottky electron gun, and a spherical aberration corrector in the illumination probe optics. A small routine was developed to deconvolute the respective compositions of γ′ and γ″ nanoprecipitates embedded in the γ matrix. Keeping the electron probe current low enough—a few hundred pA—prevented excessive irradiation damage during the acquisition of element maps and brought their spatial resolution down to the atomic column level to track their element compositions. The present results agree with and complement atomic probe tomography observations and Thermo-Calc predictions from the literature. The presence of an Al enrichment at the γ′/γ″ interface—which may control the γ″ phase coarsening—is observed in the last row of Al-Nb-Ti columns along this interface. In addition, a few columns with similar composition changes are found randomly distributed in the γ′ phase. [ABSTRACT FROM AUTHOR]

The high-temperature oxidation characteristics of Inconel 625 superalloy fabricated by additive manufacturing were studied at 900 and 1000 °C in a mixture of dry air and 12%vol water vapor. At 900 °C, oxidation in water vapor was slightly faster than oxidation in air (kpwv 900 = 3.4 × 10−3mg2cm−4 h−1 and kpa900 = 2.9 × 10−3mg2cm−4 h−1). At 1000 °C, oxidation in air (kpa1000 = 74 × 10−3mg2cm−4 h−1) occurred faster than oxidation in water vapor (kpwv1000 = 45 × 10−3mg2cm−4 h−1) although for the early oxidation up to ~ 14 h the opposite behavior was observed. Features like crack and pore formation accounted for increasing the ionic mobility through the oxide and the oxidation rate in water vapor at this temperature. Chromia Cr2O3 was the main oxide found on the surface of the alloy, but intergranular oxidation zones having Ti- and Al-rich oxides were also formed below the metal-oxide interface. Evidence of localized CrO2(OH)2 volatilization was also found. [ABSTRACT FROM AUTHOR]