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Moskal, Grzegorz. "Oxidation behavior of Co-Al-Mo-Nb and Co-Ni-Al-Mo-Nb new tungsten-free y-y' cobalt-based superalloys". OCHRONA PRZED KOROZJĄ 1, nr 9 (5.09.2017): 28–32. http://dx.doi.org/10.15199/40.2017.9.5.
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Makineni, S. K., B. Nithin i K. Chattopadhyay. "Synthesis of a new tungsten-free γ–γ′ cobalt-based superalloy by tuning alloying additions". Acta Materialia 85 (luty 2015): 85–94. http://dx.doi.org/10.1016/j.actamat.2014.11.016.
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Wang, Zihan, Jianxin Zhang, Youjian Zhang, Huixin Jin i Wenyang Zhang. "First-Principles Study of a Tungsten-Free γ–γ′ Co–Al–Mo–Nb Class Cobalt-Based Superalloy and the Alloying Effect of Ti Addition". Journal of the Physical Society of Japan 89, nr 12 (15.12.2020): 124714. http://dx.doi.org/10.7566/jpsj.89.124714.
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Leni, Desmarita, Yuda Perdana Kusuma, Muchlisinalahuddin Muchlisinalahuddin, Ruzita Sumiati i Hendri Candra Mayana. "THE IMPLEMENTATION OF PANDAS PROFILING AS A TOOL FOR ANALYZING MECHANICAL PROPERTIES DATA OF NICKEL-BASED SUPERALLOYS BASED ON ALLOY CHEMICAL COMPOSITION". International Journal of Innovation in Mechanical Engineering and Advanced Materials 4, nr 3 (31.05.2023): 86. http://dx.doi.org/10.22441/ijimeam.v4i3.19439.
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The purpose of this study is to evaluate the mechanical properties of nickel-based superalloys with variations in alloy chemical compositions using the Exploratory Data Analysis (EDA) method with the assistance of the pandas profiling library on Google Colab. In this study, data from 312 tensile tests of nickel-based superalloys were used as research samples, with alloy chemical compositions including carbon (C), manganese (Mn), silicon (Si), chromium (Cr), nickel (Ni), molybdenum (Mo), vanadium (V), nitrogen (N), niobium (Nb), cobalt (Co), tungsten (W), aluminum (Al), and titanium (Ti), as well as mechanical properties such as yield strength (YS), tensile strength (TS), and elongation (EL). The methodology used in this study was the EDA method with the assistance of the pandas profiling library on Google Colab, which enables the automatic creation of a dataset report, presenting information on various aspects such as data structure, descriptive statistics, correlation, distribution, and missing values. The results show that yield strength has a fairly high correlation with titanium (0.51), medium correlations with nickel (0.25), vanadium (0.2), and cobalt (0.2). Tensile strength in nickel-based superalloys has a fairly high correlation with yield strength (0.88), carbon (0.49), and cobalt (0.55), and medium correlations with titanium (0.25) and vanadium (0.25). Elongation in nickel-based superalloys has a negative and fairly high correlation with tensile strength (-0.62) and yield strength (-0.58). Some warnings for missing data and zero values in some variables were identified. These results indicate that the pandas profiling library can be used as a tool to analyze the data of mechanical properties of nickel-based superalloys quickly and easily, and provide clear information on data patterns, data structure, and correlation among data.
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Helbig, Christoph, Alex M. Bradshaw, Andrea Thorenz i Axel Tuma. "Supply Risk Considerations for the Elements in Nickel-Based Superalloys". Resources 9, nr 9 (31.08.2020): 106. http://dx.doi.org/10.3390/resources9090106.
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Nickel-based superalloys contain various elements which are added in order to make the alloys more resistant to thermal and mechanical stress and to the adverse operating environments in jet engines. In particular, higher combustion temperatures in the gas turbine are important, since they result in higher fuel efficiency and thus in lower CO2 emissions. In this paper, a semi-quantitative assessment scheme is used to evaluate the relative supply risks associated with elements contained in various Ni-based superalloys: aluminium, titanium, chromium, iron, cobalt, niobium, molybdenum, ruthenium, tantalum, tungsten, and rhenium. Twelve indicators on the elemental level and four aggregation methods are applied in order to obtain the supply risk at the alloy level. The supply risks for the elements rhenium, molybdenum and cobalt are found to be the highest. For three of the aggregation schemes, the spread in supply risk values for the different alloy types (as characterized by chemical composition and the endurance temperature) is generally narrow. The fourth, namely the cost-share’ aggregation scheme, gives rise to a broader distribution of supply risk values. This is mainly due to the introduction of rhenium as a component starting with second-generation single crystal alloys. The resulting higher supply risk appears, however, to be acceptable for jet engine applications due to the higher temperatures these alloys can endure.
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Bocchini, Peter J., Chantal K. Sudbrack, Daniel J. Sauza, Ronald D. Noebe, David N. Seidman i David C. Dunand. "Effect of tungsten concentration on microstructures of Co-10Ni-6Al-(0,2,4,6)W-6Ti (at%) cobalt-based superalloys". Materials Science and Engineering: A 700 (lipiec 2017): 481–86. http://dx.doi.org/10.1016/j.msea.2017.06.018.
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Singh, Mahander Pratap, Emmanuel Femi Olu, Prafull Pandey i Kamanio Chattopadhyay. "Thermophysical and magnetic properties of Co-Ni-Mo-Al-Ta class of tungsten free Co-based superalloys". Journal of Alloys and Compounds 879 (październik 2021): 160379. http://dx.doi.org/10.1016/j.jallcom.2021.160379.
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Migas, Damian, Grzegorz Moskal i Tomasz Maciąg. "Thermal analysis of W-free Co–(Ni)–Al–Mo–Nb superalloys". Journal of Thermal Analysis and Calorimetry 142, nr 1 (24.02.2020): 149–56. http://dx.doi.org/10.1007/s10973-020-09375-7.
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Abstract In this investigation, the thermal analysis of W-free cobalt-based superalloys based on Co–Al–Mo–Nb and Co–Ni–Al–Mo–Nb systems was performed. The analysis was performed at different stages of heat treatment process. The differential thermal analysis (DTA) was utilized for the determination of characteristic temperatures related to microstructural changes. First of all, the DTA analysis was carried out for discussing as-cast alloys in the temperature range of 40–1500 °C. The results showed thermal effects connected with melting and important order–disorder transition. The temperature range of 1200–1250 °C was chosen for performance of a first heat treatment operation for the investigated alloys. Specimens were annealed at selected temperature for 5 h. The microstructure of alloys after solution heat treatment was analyzed as well. Afterward, the solutionized specimens were subjected to the further thermal analysis in order to select the aging temperature according to the order–disorder transformation related to formation of γ′ phase with overall formula Co3(Al,X). Five aging variants were performed in the temperature range of 800–1000 with a step of 50 °C. After each stage of heat treatment, SEM/EDS analysis and hardness measurements were performed.
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Wang, Zhenhua, Jiheng Jia, Liyan Cao, Ning Sun i Yulin Wang. "Microstructure and Mechanical Properties of Spark Plasma Sintered Si3N4/WC Ceramic Tools". Materials 12, nr 11 (10.06.2019): 1868. http://dx.doi.org/10.3390/ma12111868.
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Silicon nitride (Si3N4) based ceramic tools exhibit good machinability in cutting materials such as gray cast iron, ductile iron, malleable cast iron, and superalloys due to excellent high-temperature mechanical properties. In this paper, high-performance Si3N4-based ceramic tools containing tungsten carbide (WC) and cobalt (Co) were studied. Effects of the WC content and Co content on mechanical properties and a microstructure of Si3N4-based ceramic materials were analyzed. Results showed that Si3N4-based ceramic material containing 10 wt % WC and 1 wt % Co had the best comprehensive mechanical properties at a sintering temperature of 1650 °C and holding time of 6 min, achieving Vickers hardness, fracture toughness, and room temperature bending strength of 16.96 GPa, 7.26 MPa·m1/2, and 1132 MPa, respectively. The microstructure of Si3N4-based ceramic tool material is uniform without obvious abnormal growth. The Si3N4-based ceramic tool was mainly composed of α-Si3N4, β-Si3N4, and WC phases.
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Yui, Akinori, Takayuki Kitajima, Peter Krajnik, Katsuko Harano, Hitoshi Sumiya i Hajime Ono. "Effect of Cutting Fluid on Diamond Tool Life under Micro V-Groove Turning of Cobalt-Free Tungsten Carbide". Advanced Materials Research 1017 (wrzesień 2014): 181–86. http://dx.doi.org/10.4028/www.scientific.net/amr.1017.181.
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Micro-machining of hard dies and molds for optical parts or precision instruments is required to extend die and mold life. This paper investigates the effect of cutting fluid on diamond tool life under micro V-groove turning of cobalt-free tungsten carbide. Zinc dialkyldithiophosphate fluid (ZnDTP) displayed excellent diamond tool wear resistance in previous experiments. The performance of this cutting fluid is compared to newly developed vegetable oil based cutting fluid with dispersed MoS2 nanotubes. This paper investigates nanopolycrystalline diamond (NPD) tool life with a rake angle of 0° and-30° under continuous micro V-groove turning (i.e. face turning), of cobalt-free tungsten carbide using the developed cutting fluids. Superior diamond tool edge wear resistance is observed when using the dispersed MoS2 nanotubes in vegetable oil and using a NPD tool with a-30° rake angle.
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Niki, Takahiro, Kazuhiro Ogawa i Tetsuo Shoji. "Segregation of Alloying Elements of Directionally Solidified Nickel Based Superalloy CM247LC during Creep Degradation Process". Key Engineering Materials 353-358 (wrzesień 2007): 537–40. http://dx.doi.org/10.4028/www.scientific.net/kem.353-358.537.
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The mechanism of the degradation process of nickel based superalloy CM247LC under creep loading was analyzed by considering the microscopic chemical composition of the material such as phase boundary of γ and γ’ phases. In this study, a Directionally Solidified (DS) nickel-based superalloys CM247LC was used as test specimens. The creep test was performed at 900oC under an uni-axial stress of 216 MPa. Each specimen was creep ruptured and interrupted at different hours and then analyzed. The change of chemical composition around the interface analyzed precisely by used Auger Electron Spectroscopy (AES). It was found that the local enrichment or lack of cobalt and chromium was found at the interface. This tendency was not found in the stress free area. Since chromium is the well-known element that dominates the degradation of this material, such an enrichment or lack of cobalt and chromium may play an important role for forming a crack propagation path near the interface. This local segregation should be analyzed further to make clear degradation mechanism of this material.
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Devaux, Alexander, Eric Georges i Philippe Héritier. "Development of New C&W Superalloys for High Temperature Disk Applications". Advanced Materials Research 278 (lipiec 2011): 405–10. http://dx.doi.org/10.4028/www.scientific.net/amr.278.405.
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The enhancement of efficiency in gas turbine engines requires the development of new superalloys capable of withstanding higher temperatures. The development of novel industrial cast and wrought (C&W) disk alloys with required combination of strength, creep and fatigue resistances at 700°C is particularly desired due to the expensive cost of powder metallurgy. In this context, new C&W disk alloys were recently developed to fulfill these requirements. TMW4 shows higher properties than the current C&W disk alloy despite an expensive cost due to its high cobalt content, where as 718Plus presents a moderate cost with restricted creep properties at 700°C compared to the current U720Li disk alloy. The new nickel base superalloys developed by Aubert & Duval were therefore designed to offer a better compromise between high temperature properties at 700°C and cost. This paper describes the alloy metallurgical features and is especially focused on the alloy design which is extensively based on phase diagram modeling. The study was firstly carried out on small ingots of 6 kg to optimize the chemistry before forging 200 kg ingots by industrial processes. The ability to be processed by the conventional cast & wrought route and the control of the highly expensive elements contents confer to the alloys an attractive cost comparable to that of 718Plus alloy. The high amount of ’ and the molybdenum-tungsten levels insure higher creep and tensile properties than those obtained with 718Plus.
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Dadvand, Nazila, Mina Dadvand i Georges Kipouros. "Reversed Pulse Plating of Silver-Cobalt for Connector Applications". International Symposium on Microelectronics 2018, nr 1 (1.10.2018): 000403–8. http://dx.doi.org/10.4071/2380-4505-2018.1.000403.
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Abstract The manuscript describes the use of anti-galling silver-cobalt alloy as a novel metallic contact finish for connector applications. The purpose of this work was to develop a cost-effective and cyanide-free and self-lubricated silver-cobalt alloy deposited using reversed pulse electrodeposition process for silver-based contact finishes in electrical contacts applications. The manuscript describes a novel silver-cobalt alloy deposited through reversed pulse-electroplating process that provides exceptionally low friction coefficient (similar to hard gold) and outstanding wear resistance compared to standard silver and any commercially available electroplated silver alloys such as silver-tin, silver palladium, silver antimony, silver-bismuth, silver-tellurium, and silver-tungsten.
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Novák, Pavel, Tiziano Bellezze, Marcello Cabibbo, Ernst Gamsjäger, Manfred Wiessner, Dragan Rajnovic, Lucyna Jaworska i in. "Solutions of Critical Raw Materials Issues Regarding Iron-Based Alloys". Materials 14, nr 4 (13.02.2021): 899. http://dx.doi.org/10.3390/ma14040899.
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The Critical Raw Materials (CRMs) list has been defined based on economic importance and supply risk by the European Commission. This review paper describes two issues regarding critical raw materials: the possibilities of their substitution in iron-based alloys and the use of iron-based alloys instead of other materials in order to save CRMs. This review covers strategies for saving chromium in stainless steel, substitution or lowering the amounts of carbide-forming elements (especially tungsten and vanadium) in tool steel and alternative iron-based CRM-free and low-CRM materials: austempered ductile cast iron, high-temperature alloys based on intermetallics of iron and sintered diamond tools with an iron-containing low-cobalt binder.
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Chkhartishvili, Levan, Archil Mikeladze, Nikoloz Jalabadze, Lili Nadaraia, Tamar Korkia i Roin Chedia. "New Low-Temperature Method of Synthesis of Boron Carbide Matrix Ceramics Ultra-Dispersive Powders and their Spark Plasma Sintering". Solid State Phenomena 331 (29.04.2022): 173–84. http://dx.doi.org/10.4028/p-8n6hzy.
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The ultra-dispersive powders of pre-ceramic precursors for boron carbide based composites were obtained by relatively low-temperature (at 200 – 1000 °C) synthesis from liquid charges containing available compounds such as salts and oxides. Boron carbide matrix ceramics were compacted by their reactive spark plasma sintering (SPS) at 1500 – 1700 °C. It is noted that the X-ray diffraction (XRD) peaks corresponding (m)ZrO2 and WC phases presented in the synthetic pre-ceramic precursors disappear after the SPS is conducted at 1500 °C. It is established that the addition of tungsten and cobalt compounds promotes both the low-temperature synthesis of ceramic components and sintering processes of their powders. Energy dispersive X-ray (EDX) analysis showed that the ceramics contain a small amount of Co (0.8 – 2 wt.%). The density of samples of cobalt-containing ceramics B4C–ZrB2–W2B5–Co is higher compared to that of cobalt-free ceramics B4C–ZrB2–W2B5.
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Torkashvand, Kaveh, Shrikant Joshi i Mohit Gupta. "Advances in Thermally Sprayed WC-Based Wear-Resistant Coatings: Co-free Binders, Processing Routes and Tribological Behavior". Journal of Thermal Spray Technology 31, nr 3 (luty 2022): 342–77. http://dx.doi.org/10.1007/s11666-022-01358-4.
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AbstractA growing understanding of wear behavior of various thermally sprayed ceramic–metallic matrix coatings has occurred over recent years. This has resulted from the continuous evolution in spraying methods as well as material feedstock, and the corresponding new aspects of the field that have been thoroughly explored. This paper aims to review recent developments in thermally sprayed tungsten carbide-based coatings, with specific emphasis on evaluating alternative binders, processing routes and tribological behavior of the coatings. A comprehensive evaluation of various compositions as binders for WC-based coatings, considering environmental concerns and market requirements has been carried out. The properties and performance of various potential alternatives for cobalt as a conventional binder for these coatings have been assessed. Moreover, different thermal spray methods have been reviewed, particularly highlighting the role of processing parameters, phase change and feedstock characteristics in the high-velocity oxy-fuel (HVOF) and high-velocity air fuel (HVAF) techniques. A comparison is made between HVAF and HVOF coatings in terms of their performance under different wear environments. Finally, various scenarios of material removal in HVAF and HVOF coatings, under various wear conditions, have also been reviewed.
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Hitzler, Leonhard, Frank Alifui-Segbaya, Philipp Williams, Burkhard Heine, Michael Heitzmann, Wayne Hall, Markus Merkel i Andreas Öchsner. "Additive Manufacturing of Cobalt-Based Dental Alloys: Analysis of Microstructure and Physicomechanical Properties". Advances in Materials Science and Engineering 2018 (11.11.2018): 1–12. http://dx.doi.org/10.1155/2018/8213023.
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The limitations of investment casting of cobalt-based alloys are claimed to be less problematic with significant improvements in metal additive manufacturing by selective laser melting (SLM). Despite these advantages, the metallic devices are likely to display mechanical anisotropy in relation to build orientations, which could consequently affect their performance “in vivo.” In addition, there is inconclusive evidence concerning the requisite composition and postprocessing steps (e.g., heat treatment to relieve stress) that must be completed prior to using the devices. In the current paper, we evaluate the microstructure of ternary cobalt-chromium-molybdenum (Co-Cr-Mo) and cobalt-chromium-tungsten (Co-Cr-W) alloys built with direct metal printing and LaserCUSING SLM systems, respectively, at 0°, 30°, 60°, and 90° inclinations (Φ) in as-built (AB) and heat-treated (HT) conditions. The study also examines the tensile properties (Young’s modulus, E; yield strength, RP0.2; elongation at failure, At; and ultimate tensile strength, Rm), relative density (RD), and microhardness (HV5) and macrohardness (HV20) as relevant physicomechanical properties of the alloys. Data obtained indicate improved tensile properties and HV values after a short and cost-effective heat-treatment cycle of Co-Cr-Mo alloys; however, the process did not homogenize the microstructure of the alloy. Annealing heat treatment of Co-Cr-W led to significant isotropic characteristics with increased E and At (except for Φ = 90°) in contrast to decreased RP0.2, Rm, and HV values, compared to the AB form. Similarly, the interlaced weld-bead structures in AB Co-Cr-W were removed during heat treatment, which led to a complete recrystallization of the microstructure. Both alloys exhibited defect-free microstructures with RD exceeding 99.5%.
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Zou, Qing Hua, i Zhen Guo Wang. "Experiment on Doping Rare Earth Diamond Tools Matrix Composites with Fe Replacing Co". Applied Mechanics and Materials 692 (listopad 2014): 200–205. http://dx.doi.org/10.4028/www.scientific.net/amm.692.200.
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This paper makes the experimental experiment on adding rare earth elements cerium doped in diamond matrix composites. Based on the doping of rare earth in metal powders including tungsten carbide, iron and nickel, the cobalt in diamond matrix is entirely with iron and the process route of rare earth doping is indicated. The performance of matrix composites with rare earth elements and free of rare earth elements is measured and the results obtained show that the flexural strength, the hardness and the impact ductility of matrix composites with rare earth elements are improved and the flexural strength increases by 10~62% over that of the composites free of rare earth elements, and the impact ductility by about 5% correspondently. We have successfully studied out the rare-earth diamond tool matrix composites replacing Co with Fe, bearing good practical service performance and low price, and have made corresponding diamond bit.
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Jeong, Ye-Seon, Kyeong-Min Kim, Hyungsoo Lee, Seong-Moon Seo i Eun-Joon Chun. "Evaluation and Control of Liquation Cracking Susceptibility for CM247LC Superalloy Weld Heat-Affected Zone via Visualization-Based Varestraint Test". Korean Journal of Metals and Materials 59, nr 7 (5.07.2021): 445–58. http://dx.doi.org/10.3365/kjmm.2021.59.7.445.
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The metallurgical aspects of weld cracking in Ni-based superalloys remain relatively unexplored in existing research. The present study performed comprehensive metallurgical and manufactural investigations into the weldability of an Ni-based superalloy, CM247LC, from the viewpoint of the liquation cracking behavior and its susceptibility. Metallurgical solutions to suppress the liquation-cracking susceptibility were derived via the visualization-based Varestraint test, and the possibility of liquation crack-free welding was explored by employing pre-weld heat treatments and laser beam welding. The alloy that was subjected to aging treatment exhibited the lowest liquation-cracking susceptibility (liquation cracking temperature range: 66 K), while the as-cast alloy specimen exhibited the highest liquation-cracking susceptibility (liquation cracking temperature range: 620 K). The metallurgical mechanisms of the liquation cracking susceptibility of as-cast CM247LC weld were elucidated via microstructural analyses and thermodynamic calculations. The suppressed liquation cracking susceptibility of the aged CM247LC can be attributed to the MC-type carbide fraction and homogenized matrix phase, as compared with those of as-cast CM247LC. The aged CM247LC specimen was subjected to gas tungsten arc welding to validate its minimal liquation-cracking susceptibility. The results confirmed the suppression of liquation cracking, due to the low susceptibility of the specimen. However, crackfree welds could not be obtained. Finally, metallurgically sound welds without liquation cracks were successfully obtained via laser beam welding. The outcomes of the present study will facilitate the generation of electric power from fossil fuels via a clean and efficient gas turbine-based power generation cycle.
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Ziemnicka-Sylwester, Marta. "Superhard TiB2 - Based Composites with Different Matrix Fabricated from Elemental Powders by SHS-p-HIP". Advances in Science and Technology 77 (wrzesień 2012): 146–52. http://dx.doi.org/10.4028/www.scientific.net/ast.77.146.
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TiB2is a superhard, high-temperature and high corrosion resistant material and it is under consideration for tungsten-free cutting tools and high temperature structural applications. Although such a covalent compound requires significantly elevated temperature for the consolidation, great exothermicity of TiB2synthesis by means of SHS (Self-propagating High-temperature Synthesis) can be “ïn situ” utilized. In this study, TiB2-based composites are fabricated from titanium, boron and binder metal. In order to optimize consolidation process and improve fracture toughness of the products, three types of binder, based on cobalt, nickel or copper were investigated. In respect to hardness, limited amount of binder, 5, 10 or 15 vol.% respectively, were applied; each time 5 vol.% of Ti addition for reaction with boron completeness was used. The TiB2based composites were fabricated from elements in one process by means of the SHS process combined with p-HIP (pseudo-hot isostatic pressing) method. The raw elemental powders were homogenized by wet mixing using ball milling technique. Dried mixtures were pressed into a compact, coiled by heating element and then exposed to the SHS-p-HIP process. After SHS initiation, the compact was pressed pseudo-isostatically under pressure of 190MPa for 5 min. The sintering additives and their concentrations significantly affected the consolidation process as well as the properties of composites. The highest hardness was obtained for samples sintered with cobalt, containing intermetallic binder. However, elemental metal binder was detected as a main component for samples sintered with copper. The relative density, SEM microstructure, phase composition and hardness are compared in this study.
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Blagoveshchenskiy, Yu V., N. V. Isaeva, E. A. Lantsev, M. S. Boldin, V. N. Chuvil’deev, A. V. Nokhrin, A. A. Murashov i in. "Spark plasma sintering of WC – 10 Co nanopowders with various carbon content obtained by plasma-chemical method". Perspektivnye Materialy, nr 8 (2020): 73–86. http://dx.doi.org/10.30791/1028-978x-2020-8-73-86.
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The features of high-speed sintering of WC – Co nanopowders with various contents of excess carbon (colloidal graphite) were studied. To obtain powders, a process was used that included plasma-chemical and low-temperature syntheses and a chemical-metallurgical method of applying ultrathin cobalt layers by precipitation from a solution of salts. The consolidation of powder materials was carried out by the method of high-speed Spark Plasma Sintering. It was found that an increase in the concentration of free carbon (colloidal graphite) has the greatest effect on the shrinkage and sintering rate at the stage of intense shrinkage of WC-Co nanopowders. It is shown that an increase in the carbon content in the composition of nanopowders leads to a decrease in the value of sintering activation energy at the stage of intense shrinkage.It has been established that the process of nanopowder compaction at the intense shrinkage stage is determined by the intensity of the plastic flow and the grain boundary diffusion of cobalt. It is shown that the mechanism of plastic deformation of the γ-phase based on cobalt corresponds to the Coble diffusion creep. It was found that an increase in carbon content leads to decreased in activation energy at the intense shrinkage and does not significantly affect at stage III of sintering where decrease in the shrinkage intensity is observed. It was shown that a decrease in the sintering activation energy is due to a decrease in the tungsten concentration in the γ-phase.
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Cadden, Thomas, Sudipta Roy i Edward Brightman. "Hydrothermally Enhanced Tungsten-Tungsten Bronze (W-MxWO3) Electrodes for Pseudocapacitive Energy Storage". ECS Meeting Abstracts MA2022-02, nr 22 (9.10.2022): 942. http://dx.doi.org/10.1149/ma2022-0222942mtgabs.
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Hexagonal tungsten bronzes (h-MxWO3) are an emergent class of pseudocapacitive energy storage material: a metastable phase arranged in a hexagonal crystal structure that enhances the oxide’s rapid intercalation mechanism with impressive capacitances of over 200 F/g and excellent cyclability figures reported. A symmetrical pseudocapacitive device composed of h-MxWO3 electrodes negates the need for expensive and problematic rare minerals such as cobalt and lithium instead using low-cost tungsten whilst offering more efficient high-rate energy storage than commercial lithium-ion batteries. Hexagonal tungsten bronze has shown some promising capacitances in literature in conventional electrode configurations, i.e. composite structures with binder support materials which increase electrode mass impacting specific capacitance. If the bronze was instead grown directly upon a current-collecting substrate, this would negate the need for additional electrode components, with the entire electrode mass participating in storing charge. The present work explores this concept of a novel binder-free electrode design where the nanostructured tungsten-bronze (active material) is grown directly upon a tungsten-based substrate (current collector). This simple design offers potentially higher specific capacitances than conventionally fabricated electrodes. Nanostructured W/h-MxWO3 electrodes were fabricated in a twostep process. Firstly, tungsten foil was oxidised in hot nitric acid, forming a seed layer of monoclinic-WO3. A second step saw the hexagonal bronze deposited upon substrates through a hydrothermal dehydration reaction of sodium tungstate (Na2WO4) where the effect of the directing agent (NaCl, Na2SO4, (NH4)2SO4& Rb2SO4) on the deposited nanostructure was investigated. To assess the benefit of the acid pretreatment step, vis-à-vis a pristine untreated tungsten foil, the hydrothermal reaction was completed upon both a pristine tungsten foil and an acid treated foil. The nanostructured surface deposited from the hydrothermal reaction was characterised by SEM, and the crystal phase identified by XRD. The electrochemical behaviour was analysed using a Biologic SP-300 potentiostat in a 3-electrode cell: as-synthesised foils employed as working electrode; Pt Wire as counter electrode; a saturated calomel electrode (SCE) as reference; and 0.5M H2SO4 as electrolyte. The performance of devices fabricated from two symmetrical as-synthesised electrodes was also characterised using both the potentiostat and a NEWARE battery cycling test system in a two-electrode cell configuration. XRD analysis confirmed that hexagonal-tungsten bronzes were successfully deposited upon substrates irrespective of the substrate pretreatment. The acid pretreatment generally resulted in larger masses of bronze being deposited upon the substrate, but this did not necessarily translate to superior electrochemical performance. The choice of directing agent present in hydrothermal synthesis drastically altered the nature of the deposited layer as may be seen in the provided figure of as-synthesised electrodes (figure b-d). Sodium directed samples formed powder-like deposits (figure b), ammonium sulphate produced larger colloidal bronze layers (figure c) and rubidium sulphate developed glossy smooth sheets (figure d). Additionally, the ratio of tungstate ions (WO4 2-) to directing agent cations (M+) was identified as being critical to obtaining the hexagonal phase. The mechanical stability of the deposited bronze proved problematic, with the layer prone to delamination and disintegration from a variety of mechanisms. A bespoke electrode holder, device testing apparatus and handling procedure was therefore developed to enable repeatable electrode characterization. The cyclic voltammetry response of the hydrothermally deposited layers was typical of an intercalation system, though an initial pseudocapacitive behaviour deteriorated to a battery-like response at sweeprates above 20 mV/s. Galvanostatic charge-discharge testing displayed a significant pseudocapacitive response over limited potential windows; moving beyond these limits produced steep non-linear curves indicating a departure from pseudocapacitive charge transfer processes. The charging at current densities above 1 A/g occurred over rapid time scales showing the electrodes’ suitability for high power applications. Preliminary 3-electrode capacitance results are encouraging with specific capacitances of over 100 Fg-1 by dry mass. The tunnelated M+ ion in the bronze is found to greatly influence the electrochemical performance of the electrode. This work reports the first example of hexagonal tungsten bronze being successfully grown directly on tungsten substrates for application as energy storage electrodes. The binder free electrodes were found to deliver promising performance characteristics in both 3-electrode analysis and in a two-electrode symmetrical device. The performance so far is hampered by the mechanical fragility of the electrode structures, while scale-up of the manufacturing process may prove challenging. The observed mechanism of deposition of hexagonal tungsten bronze from solution to substrate is of interest for future work, as is the significance of tunnelated M+ cations to the hexagonal bronze (h-MxWO3) structure, stability, and electrode performance (figure a). Figure 1
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Hasan, Md Shahanur, Abdul Md Mazid i Richard Clegg. "The Basics of Stellites in Machining Perspective". International Journal of Engineering Materials and Manufacture 1, nr 2 (19.12.2016): 35–50. http://dx.doi.org/10.26776/ijemm.01.02.2016.01.
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Stellites are cobalt (Co)-based superalloys available in two main combinations: (a) a Tungsten (W) group with composition of Co-Cr-W-C, and (b) a Molybdenum (Mo) group containing Co-Cr-Mo-C. Stellites possess outstanding corrosion resistance, oxidation resistance, wear resistance, heat resistance, and low magnetic permeability. Components made of stellites work well in highly corrosive environments and maintain these advantageous properties at elevated temperatures. Components made of stellites are widely used in the oil and gas, automotive, nuclear power, paper and pulp, chemical and petrochemical, refineries, automobile, aerospace and aircraft industries. By virtue of their nonmagnetic, anticorrosive and non-reactivity to human body-fluid properties, stellites are used in medical surgery and in surgical tools, tooth and bone implants and replacements, heart valves, and in heart pacemakers. The hardness range of stellites is from 32 to 55 HRC, which makes stellites brittle materials but they have a low Young’s modulus. Due to their high hardness, dense but non-homogeneous molecular structure and lower thermal conductivity, machining operations for parts made of stellites are extremely difficult, categorising stellites as difficult-to-machine materials like Ti-alloys, inconels, composites and stainless steels. Usually, machine components made of stellites are produced by a deposition method onto steel substrates instead of expensive solid stellite bars. The rough surfaces of deposited stellites are then finished by grinding, rather than some other economic machining process, which is costly and time-consuming, making stellite products very expensive. This paper provides a basic overview of stellites applicable in engineering, their significances and specific applications, advantages and disadvantages in respect of machining processes.A brief review on experimental research on economically rational cutting parameters for turning operations of Stellite 6 using coated carbide inserts is presented in this paper. Interesting facts on the residual stresses induced by machining processes in Stellite 6 are revealed and analysed. The microhardness variation of machined surfaces of stellite 6 using different tool geometries is investigated in this research review. It is revealed that coated carbide inserts with a medium-size nose radius perform better in respect of hardness changes and heat generation, producing minimum phase changes on machined surfaces of stellite 6.
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Fang, Shiqi, Núria Salán, Christoph Pauly, Luis Llanes i Frank Mücklich. "Critical Assessment of Two-Dimensional Methods for the Microstructural Characterization of Cemented Carbides". Metals 12, nr 11 (3.11.2022): 1882. http://dx.doi.org/10.3390/met12111882.
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Cemented carbides, or hard metals, are ceramic–metal composites usually consisting of tungsten carbide particles bound by a cobalt-based alloy. They are the backbone materials for the tooling industry, as a direct consequence of the outstanding range of property combinations, depending on their effective microstructural assemblage, i.e., the physical dimensions and relative content of their constitutive phases. Hence, reliable microstructural characterization becomes key for hard metal grade selection and quality control. This work aimed to assess the practical two-dimensional characterization methods for the most important one- and two-phase properties of cemented carbides, i.e., the carbide grain size, phase fraction, carbide contiguity, and binder mean free path. Three different methods—point, line, and area analysis—were implemented to characterize four microstructurally distinct grades. The images were acquired by optical and scanning electron microscopy, with the latter through both secondary and backscattered electrons. Results were critically discussed by comparing the obtained values of properties and the different characterization methodology. Inspection technique combinations were finally ranked based on accuracy, accessibility, and operability considerations. The line method was used to analyze all the properties, the area method, for the one-phase properties, and the point method, for only the phase fraction. It was found that the combination of optical microscopy and the line analysis method was suitable for a direct inspection and rapid estimation for carbides above fine grain size. The most precise results were achieved using line analysis of the images obtained by the backscattered electrons of the scanning electron microscope.
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Moskal, Grzegorz, Damian Migas, Dawid Niemiec i Agnieszka Tomaszewska. "Thermogravimetric Investigations of Novel γ–γ′ Co-Al-W and Co-Al-Mo-Nb Cobalt-Based Superalloys". Journal of Engineering Materials and Technology 141, nr 4 (17.05.2019). http://dx.doi.org/10.1115/1.4043626.
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Cobalt-based γ–γ′ superalloys are novel heat-resistant materials suitable for high-temperature applications, such as components of the turbine engine. These alloys exhibit favorable strength and corrosion resistance at high temperatures owing to the γ–γ′ microstructure, analogous to that of Ni-based superalloys. The aim of this paper is to evaluate the oxidation behavior of basic Co-9Al-9W (at%) and new tungsten-free Co-10Al-5Mo-2Nb (at%) alloys at elevated temperatures. The investigation is concerned with thermogravimetric studies in the temperature range of 40–1200 °C. The oxidized surfaces after high temperature oxidation have been characterized using optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction analysis (XRD).
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König, Till, S. P. Hagen, S. Virtanen i M. C. Galetz. "Development of Cr and Al Pack Cementation Coatings on Co-Based γ/γ′ Superalloys". Metallurgical and Materials Transactions A, 11.09.2022. http://dx.doi.org/10.1007/s11661-022-06807-x.
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AbstractCo-based superalloys have been developed as candidate materials to replace Ni-based superalloys in hot sections of turbine engines, however, their oxidation resistance is limited. Therefore, in this work chromium and aluminum diffusion coatings were developed via the pack cementation process for novel γ/γ′-strengthened superalloys of the Co–Ni–Al–W system. This alloy system also offers the opportunity to vary the cobalt-to-nickel ratio and the tungsten content systematically to investigate their influence on the coating process. The coating process was shown to successfully enrich the surfaces of such alloys either in aluminum or chromium. For Al, the result was the formation of (Co, Ni)Al on top of an interdiffusion zone, while for chromium a Cr-rich layer in solid solution with the substrate along with the formation of σ-phase were observed. The coating formation mechanisms are discussed for both coatings in the light of activities and phase formation.
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KAYA, Esad, i Mustafa ULUTAN. "The evaluation Of The Non-Toxic Ferrous Matrix Based WC Reinforced Composites: A Review". Celal Bayar Üniversitesi Fen Bilimleri Dergisi, 27.05.2022. http://dx.doi.org/10.18466/cbayarfbe.1020170.
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Metal matrix composites are mainly used as a cutting tool insert material. These types of materials are essential to maintain desired mechanical and microstructure properties at elevated temperatures due to friction and wear. Nano sized Tungsten Carbide reinforced composites are mostly used for these conditions. The production of sintered nano sized Tungsten Carbide reinforced composites are done by using powder metallurgy. The different mass ratios of elements including mostly Cobalt and the others could be added as binder phase. The binder phase provides to metal matrix composite superior features including high elasticity, good solubility, similar thermal conduction coefficient and, effective liquid phase sintering mechanism. Cobalt is one of the base elements of high-performance superalloys and rechargeable battery technology. Also, 40% of global need supplied by a single country makes itself higher-priced. It is also known that Cobalt is a high skin allergen and carcinogenic. Together with these obstacles, the investigations of low-cost, non-toxic, or reduced-toxicity materials are always needed. In this study, the related current literature has been investigated in detail. The studies focus on an alternative matrix that providing mentioned conditions explained with pros and cons.
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Keshavarz, Mohsen K., Alexandre Gontcharov, Paul Lowden i Mathieu Brochu. "A Comparison of Weldability, Structure, and Mechanical Properties of CM64 and Tribaloy T-800 Welds for Hard-Facing of Turbine Blades". Journal of Manufacturing Science and Engineering 142, nr 10 (4.06.2020). http://dx.doi.org/10.1115/1.4047142.
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Abstract In this study, the weldability, microstructure, and tensile properties of CM64 and Tribaloy T-800 (T800) cobalt-based hard-facing materials were studied. Successful CM64 hard-facing could be achieved at ambient temperature using manual gas tungsten arc welding (GTAW-MA). It was shown that T800 welded at ambient temperature was prone to cold cracking due to a combination of low ductility with high welding stresses that limited the accommodation of residual stresses by plastic deformation within the weld beads. Sound T800 welds of various geometries and sizes were produced on cobalt- and nickel-based X-40 and Haynes 230 superalloys, respectively, using GTAW-MA when preheating above 900 °C was used. Microstructural analyses on the sound CM64 and T800 welds were performed using optical and electron microscopy and X-ray diffraction. The distribution of elements and phases in each alloy was evaluated and revealed the epitaxial dendritic structure with the Cr–W–Si-based phase in the interdendritic region in CM64 welds compared with petal-like and equiaxed hard Mo–Co–Si-based dendrites and fine particles in T800. Tensile testing from room temperature up to 1093 °C was performed on both alloys. T800 welds possessed lower ultimate tensile strengths and elongations in this temperature range when compared with the CM64 alloy. Recommendations for hard-facing of turbine engine components were provided.
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Garayt, Matthew D. L., Ning Zhang, svena yu, Jeffin James Abraham, Aidan Murphy, Roee Omessi, Ziwei Ye i in. "Single Crystal Li1+x[Ni0.6Mn0.4]1-xO2 Made by All-Dry Synthesis". Journal of The Electrochemical Society, 9.06.2023. http://dx.doi.org/10.1149/1945-7111/acdd24.
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Abstract Cobalt-free, single crystal layered-oxide positive electrode materials like Li1+x[Ni0.6Mn0.4]1-xO2 (NM64) received recent interest because of their low cost, high-voltage stability, and good cycle life. In this work, single crystal NM64 is successfully produced with a simple all-dry synthesis process that requires no water, no intermediate chemicals, and produces little waste. The all-dry synthesized NM64 has ≤ 4% nickel in the lithium layer based on Rietveld refinement of powder X-ray diffraction patterns, has a median particle size of 2-5 µm based on scanning electron microscopy and particle size analysis, and has excellent high-voltage stability at C/5 up to 4.4 V vs Li+/Li compared to a commercial material. Additionally, tungsten coating is shown to decrease the median particle size and improve the cycling stability in half cells from 91% retained capacity after 100 cycles to 93% retained capacity when 0.3% tungsten is added. It is believed that this incredibly simple process could be adopted relatively easily into current commercial positive electrode manufacturing facilities to reduce the complexity, cost, and time of manufacture.