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• 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]

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]

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. [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]

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]

In this study, the oxidation behavior of Ni-based alloys 625 and 825 in supercritical water containing 5000 ppm of dissolved oxygen at 500 °C was investigated by scanning electron microscopy coupled with energy-dispersive spectroscopy, X-ray diffraction, and laser Raman spectroscopy. Alloy 625 and 825 showed a pitting-like phenomenon after 500 h of exposure. The structure and composition of the oxides formed on alloy 625 and 825 were similar, namely, an outer layer of Fe oxides, spinel structures, and Ni(OH) 2 ; and an inner NiO layer. The mechanism for the formation of the oxide films was proposed, and the factors affecting corrosion of Ni-based alloys were discussed in detail. In addition, the corrosion resistance performance of alloy 625 and 825 was compared. [ABSTRACT FROM AUTHOR]

Large vacancy clusters, such as stacking-fault tetrahedra, are detrimental vacancy-type defects in ion-irradiated structural alloys. Suppression of vacancy cluster formation and growth is highly desirable to improve the irradiation tolerance of these materials. In this work, we demonstrate that vacancy cluster growth can be inhibited in concentrated solid solution alloys by modifying cluster migration pathways and diffusion kinetics. The alloying effects of Fe and Cr on the migration of vacancy clusters in Ni concentrated alloys are investigated by molecular dynamics simulations and ion irradiation experiment. While the diffusion coefficients of small vacancy clusters in Ni-based binary and ternary solid solution alloys are higher than in pure Ni, they become lower for large clusters. This observation suggests that large clusters can easily migrate and grow to very large sizes in pure Ni. In contrast, cluster growth is suppressed in solid solution alloys owing to the limited mobility of large vacancy clusters. The differences in cluster sizes and mobilities in Ni and in solid solution alloys are consistent with the results from ion irradiation experiments. [ABSTRACT FROM AUTHOR]

To further improve the cost-benefit of MCrAlX (X is a reactive element like Y, Hf, Ta, etc.) alloys, the microhardness, microstructure and oxidation behavior of two Ni-based alloys, Ni 60 Co 30 Al 10 and Ni 60 Co 10 Cr 20 Al 10 without reactive elements were studied by scanning electron microscopy, X-ray diffraction and microhardness Vickers. These alloys were synthesized by mechanical alloying in a high energy ball mill and conventional sintering at 1100 °C under inert atmosphere. Milling time and Cr additions have a significant effect on microhardness of as-milled and sintered samples. Bulk samples were oxidized at 1000 °C for different times to analyze the possible growth of protective oxide scale, as well as the effect of Cr addition on the chemical composition of the oxide scale. After 3 h of oxidation the formation of Al 2 O 3 oxide scale in the Ni 60 Co 30 Al 10 alloy is evident. By reducing the Co content and incorporating 20 wt.% of Cr, the formation of an Al 2 O 3 oxide scale with the presence of Cr 2 O 3 was observed. Even the formation of homogeneous, continuous and protective oxide products in the surface of samples is evident, the microstructural changes after oxidation treatments have a significant effect on the decrease in microhardness of both alloys. [ABSTRACT FROM AUTHOR]

Highlights: [•] Prepared the Ni–P/Ni3.1B composite alloy coating by electroless plating. [•] Sodium alginate was applied as surfactant for Ni3.1B dispersing. [•] The Ni–P/Ni3.1B coating was amorphous in as-plated condition. [•] The coating crystallized to form Ni–P–B coating after heat-treatment. [•] The Ni–P/Ni3.1B composite alloy coating has good solderability and corrosion resistance. [ABSTRACT FROM AUTHOR]

Ni-based alloys are widely used in power generation and their oxidation behaviour in the uncoated state is of interest, especially the impact of water vapour in the air on the formation of a protective underlying alumina scale. High-temperature X-ray diffraction was applied to investigate in situ the oxide scale formation in the initial state on the alumina formers CM247DS and CMSX4 in comparison to the chromia formers IN792 and SCA425+. Post-oxidation analysis was performed by field emission scanning electron microscopy. The samples were oxidised for 100 h at 950°C in dry air and in air with 20% relative moisture in the high temperature device on the X-ray diffractometer. In dry air, CM247 and CMSX-4 form α-Al2O3 from the beginning simultaneously with spinels and nickel oxide. The alumina scale underlies the spinels which spall partially on cooling. When adding water vapour, the same oxides were formed simultaneously resulting in a comparable oxide scale. IN792 forms in dry air mainly NiAl2O4 and transitionally CrO2 under laid by an alumina scale. With water vapour, Cr2O3 forms and the underlying alumina scale shows a non coherent dendritic structure. SCA425+ forms in dry air Cr2O3 and Cr containing mixed oxides and with water vapour a more coherent alumina scale than IN792. [ABSTRACT FROM AUTHOR]

Abstract: Metal matrix composite (MMC) coatings composed of nickel-based matrices and tungsten carbides (WC/W2C) are frequently used to solve problems of reduced life time under severe abrasive and corrosive conditions. The influence of processing conditions on the carbide/matrix interface was studied in the liquid-sintering process with a well defined temperature/time profile. Evaluation of the sintered samples by optical microscopy (OM) showed formation of an interface layer between matrix and carbides. SEM/EDS analysis indicated the formation of mixed Ni- and W-rich carbides on the interface microstructures. XRD measurements revealed the formation of Ni3B. The layer thicknesses were determined quantitatively by OM-image analysis. The hardness profiles across the interface were examined by nanoindentation. Furthermore, scratch tests were performed for the characterisation of carbide bonding in the matrix and evaluation of the influence of the interface layer on the single abrasion behaviour of the MMC samples. Results show that the carbide/matrix bonding and the single abrasion behaviour were dependent on the gradient of the micro-mechanical properties. Increasing processing temperature or time increased the hardness gradient and consequently decreased the bonding between carbide and matrix. Additions of chromium and iron in the matrix powder caused an improvement of the bonding and the abrasion behaviour under 2-body-condition of the MMC samples. [Copyright &y& Elsevier]

Abstract: Hard-particle metal–matrix composites (MMC) are generally used to increase the lifetime of machinery equipment exposed to severe wear conditions. Depending on the manufacturing technology, dissolution reactions of hard phases undergo different temperature/time profiles during processing affecting the microstructure and mechanical properties of the MMCs. Therefore, quantification of the carbide dissolution effects on the microstructure and micro-mechanical properties is the key to success in the development and optimisation of MMCs. Dissolution kinetics of WC/W2C in Ni-based matrices were determined in the liquid-sintering with a well-defined temperature/time profile. Microscopic evaluation of the samples showed two intermediate layers between matrix and carbides. The layer thicknesses were quantitatively determined using image analysis. A kinetics relationship was used for modelling the interface layer growth as a function of processing time, temperature and Cr-addition. Furthermore, the micro-mechanical properties of the intermediate layers were examined using nanoindentation. Based on the chemical composition and the hardness of the intermediate layers, formation of mixed Ni- and W-carbides and/or borides on the interface microstructures was indicated. Results showed that the chemical composition and the micro-mechanical properties were almost constant within all the detected layers in the interface zone between matrix and carbides, indicating that the microstructure gradients were most dependent on the intensity of the MMC processing. [ABSTRACT FROM AUTHOR]

Abstract: Laser consolidation (LC) is an emerging manufacturing process that produces net shape functional and metallurgically sound components by material addition based on a CAD model. Due to the rapid solidification inherent to the process, LC materials generally have excellent material properties. However, there is limited information available on the fatigue properties of LC materials. Throughout this work, the fatigue behavior of LC IN-625 was evaluated at both room temperature and 650°C and compared with wrought and investment cast IN-625 materials. The results show that the LC IN-625 has a fatigue resistance higher than the cast material but lower than the wrought material. Tensile and fatigue test results along with the examination of microstructures and crack initiation sites are presented. [Copyright &y& Elsevier]

The drop of ferromagnetic moment in the ternary solid solutions Ni1-x-yCuxDy, (D = Zn, Si, Au, Al) is analyzed in terms of the statistical model of the environment-dependent moments. This probabilistic model shows that the disappearing of one Ni atom ferromagnetic moment can be assigned to the replacement of at least four Ni–Ni bindings, out of twelve, in pure nickel. This paper aims at discussing all these features that, from the point of view of macroscopic equilibrium states, are related to the distribution of local bonds, provided by the peripheral electrons of the substitute atoms dissolved in the Ni matrix. [ABSTRACT FROM AUTHOR]

Different Ni-based alloys with various compositions were prepared by varying the amounts of beryllium. Effect of the amount of beryllium added to the alloy on its corrosion in an electrolyte solution of artificial saliva was investigated. Fractal dimension was used as a quantitative factor for surface analysis of the alloys before and after storage in the artificial salvia. The fractal dimensions of the electrode surfaces were determined by means of the most reliable method in this context viz. time dependency of the diffusion-limited current for a system involving “diffusion towards electrode surface”. The results showed that increase of the beryllium amount in the alloy composition significantly increases the alloy corrosion. It is accompanied by increase of the fractal dimension and roughness of the electrode surface, whereas a smooth and shiny surface is required for dentures. From the methodology point of view, the approach utilized for fractal analysis of the alloy surfaces (Au-masking of metallic surfaces) is a novel and efficient method for study of denture surfaces. Generally, this approach is of interest for corrosion studies of different metals and alloys, particularly where changes in surface structure have a significant importance. [Copyright &y& Elsevier]

Transmission electron microcopy (TEM) analysis was employed to characterize the deformation mechanisms in X-750 Ni-based superalloy. Both in-situ and ex-situ tensile tests were carried out at room temperature to observe the dislocation structure and trace the interaction between the γ'-precipitates and dislocations. The deformation mechanism was found to be planar slip which resulted in the formation of planar slip bands. This was attributed to the low stacking fault energy of X-750 alloy as well as the shearing of a high density of ordered γ'-precipitates. The shearing of γ'-precipitates occurred through an Anti-phase boundary (APB) mechanism evidenced by paired superlattice dislocations or a Stacking Fault (SF) mechanism by partial dislocations evidenced by isolated stacking faults within the γ'-precipitates. Unlabelled Image • The deformation mechanism has planar slip characteristic rather than wavy slip evidenced by planar slip bands. • Gamma-prime precipitate is sheared by dislocations which promotes the planarity of slip in deformation. • Precipitates shearing occur through an anti-phase boundary mechanism and stacking fault mechanism. [ABSTRACT FROM AUTHOR]

Ni-(3~10) Ta and Ni-(3~10) Y alloys were fabricated by vacuum arc melting. The oxidation resistance of the alloys was studied by cyclic and isothermal oxidation tests at 800 °C in static air. The present work focused on the investigation of the effects of the alloying elements (Ta and Y) on the oxidation behavior of Ni-based alloys. The oxidation behavior of alloys was evaluated by mass gain, composition, as well as the microstructure of oxidized products. The experimental results indicated that Ta at a low content (3 wt %) had a positive role in enhancing oxidation resistance by decreasing the oxygen vacancy concentration of the oxide layer to prevent the inward diffusion of oxygen during oxidation, and the mass gain decreased from 2.9 mg·cm−2 to 1.7 mg·cm−2 (800 °C/200 h), while Y (3~10 wt %) degraded the oxidation resistance. However, it is worth mentioning that the pinning effect of Y2O3 increased the adhesion between the substrate and oxide layer by changing the growing patterns of the oxide layer from a plane growth to fibrous growth. Among the results, the bonding of the substrate and oxide layer was best in the Ni-3Y alloys. [ABSTRACT FROM AUTHOR]