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Artykuły w czasopismach na temat "Co-Mo-Al Alloys"
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Davidov, D. I., Igor Ezhov, Nikolay A. Popov i Nataliya Kazantseva. "Mechanical Properties of Co-Al-Mo-Nb Intermetallic Alloys". Key Engineering Materials 910 (15.02.2022): 1121–26. http://dx.doi.org/10.4028/p-3102k8.
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The results of the experimental study of the mechanical properties and structure of the Co-9.5Al-2.9Mo-4Nb, Co-9.1Al-5.2Mo-4.7Nb, and Co-8.9Al-6.5Mo-9.3Nb alloys were presented. The Young’s moduli in the studied alloy samples were found to be smaller than those of Ni3Al-based and Co3(Al,W)-based alloys. The eutectic structure was observed in all studied alloys. Cuboids of the Co3(Al,Nb,Mo) intermetallic compound with L12 crystal structure were found by TEM study.
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Zhang, Qing Quan, Ming Yang Li, Ran Wei, Hui Yun Wu i Zhen Rui Li. "Research on Effect of Alloy Elements on Equilibrium and Properties of Ni-Cr-Co Type Nickel-Based Superalloy". Materials Science Forum 849 (marzec 2016): 513–19. http://dx.doi.org/10.4028/www.scientific.net/msf.849.513.
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Ni-Cr-Co type Nickel-based super alloy Inconel 740H was studied. The effect of Nb, Al and Ti on the equilibrium of this alloy was analyzed by JMatPro software. The amount of Ti and Nb should be controlled by 1.50wt.%, and meanwhile, Al should be 1.0-2.0wt.%. If Mo and W were added the amount of Mo should be in the range of 1.0-2.0wt. %, and W should be about 1.0wt.%. Based on these results, three types of new alloys were designed, which contain Ni-Cr-Co-Mo type (1#), Ni-Cr-Co-W type (2#) and Ni-Cr-Co-Mo-W type (3#). Compared with the Ni-Cr-Co type Inconel 740H alloy, the room temperature strength, high temperature strength and high temperature durable performance of the three new alloys improved, which can provide the evidence and reference to optimize the chemical composition of Inconel 740H alloy, i.e., adding 1.50wt.% Mo and 1.0wt.% W individually or together.
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Davydov, Denis, Nataliya Kazantseva, Nikolai Popov, Nina Vinogradova i Igor Ezhov. "Phase Transitions in the Co–Al–Nb–Mo System". Metals 11, nr 12 (23.11.2021): 1887. http://dx.doi.org/10.3390/met11121887.
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Phase transitions in the Co-rich part of the Co–Al–Nb–Mo phase diagram are studied by energy dispersive spectroscopy (EDS), X-ray analysis, transmission electron microscopy (TEM), and differential scanning calorimetry (DSC) measurements. The obtained results were compared with the results for alloys of the binary Co–Al and ternary Co–Al–Nb, and Co–Al–Mo systems. Formation of the intermetallic phase with the L12 structure was found in a range of alloys with 10 at.% Al, 2–9 at.% Nb, and 3–7 at.% Mo. Intermetallic compound Co2Nb, Laves phase with the different chemical composition and crystal structure (C14 and C36) was detected in the Co–Al–Nb and Co–Al–Nb–Mo samples after vacuum solution treating at 1250 °C for 30 h.
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Fan, Fei, Hao Sun, Di Zhao i Jiang Bo Sha. "Effect of Mo on the High Temperature Oxidation Behavior of Co-Al-W Based Alloys". Materials Science Forum 747-748 (luty 2013): 754–59. http://dx.doi.org/10.4028/www.scientific.net/msf.747-748.754.
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2 at.% and 4 at.% Mo were added to Co-9Al-9W-2Ta-0.02B alloy to replace W (hereafter referred to as the alloys of 2Mo and 4Mo, respectively; Mo-free alloy was referred to as the 0Mo alloy). The effects of Mo additions on the high temperature oxidation behavior of the alloys at 800 °C in air have been studied. The results indicated that, after oxidation in air at 800 °C for 100 h, the oxide film of the 0Mo alloy remained intact, but the cracking and spallation of the oxide film took place in the alloys of 2Mo and 4Mo. Oxidation kinetic curves revealed weight gain per unit area of the 0Mo alloy was 36.86 mg·cm-2, which was lower than that of the alloys of 2Mo (65.16 mg·cm-2) and 4Mo (48.54mg·cm-2). These suggested that the 0Mo alloy displayed superior oxidation resistance compared to the alloys of 2Mo and 4Mo caused by the formation of volatile MoO3 oxide, and sharp compressive stress formed in the outer layer during the oxidation. The oxide layer was composed of three layers of the Co3O4 + CoO outer layer, middle complex oxide layer containing Co, Al and W (Mo), inner Al2O3 layer and γ/Co3W zone adhere to the γ/γ' substrate.
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Nohira, Naoki, Keiko Widyanisa, Wan-Ting Chiu, Akira Umise, Masaki Tahara i Hideki Hosoda. "Effects of 3d Transition Metal Substitutions on the Phase Stability and Mechanical Properties of Ti–5.5Al–11.8[Mo]eq Alloys". Materials 16, nr 13 (22.06.2023): 4526. http://dx.doi.org/10.3390/ma16134526.
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The phase stability, mechanical properties, and functional properties of Ti–5.5Al–11.8[Mo]eq alloys are focused on in this study by substituting 3d transition metal elements (V, Cr, Co, and Ni) for Mo as β-stabilizers to achieve similar β phase stability and room temperature (RT) superelasticity. The ternary alloy systems with the equivalent chemical compositions of Ti–5.5Al–17.7V, Ti–5.5Al–9.5Cr, Ti–5.5Al–7.0Co, and Ti–5.5Al–9.5Ni (mass%) alloys were selected as the target materials based on the Mo equivalent formula, which has been applied for the Ti–5.5Al–11.8Mo alloy in the literature. The fundamental mechanical properties and functionalities of the selected alloys were examined. The β phase was stabilized at RT in all alloys except for the Ti–Al–V alloy. Among all alloys, the Ti–Al–Ni alloy exhibited superelasticity in the cyclic loading–unloading tensile tests at RT. As a result, similar to the Ti–5.5Al–11.8Mo mother alloy, by utilizing the Mo equivalent formula to substitute 3d transition metal elements for Mo, a RT superelasticity was successfully imposed.
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Inoue, Akihisa, Bao Long Shen i Akira Takeuchi. "Syntheses and Applications of Fe-, Co-, Ni- and Cu-Based Bulk Glassy Alloys". Materials Science Forum 539-543 (marzec 2007): 92–99. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.92.
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This paper reviews our recent results of the formation, fundamental properties, workability and applications of late transition metal (LTM) base bulk glassy alloys (BGAs) developed since 1995. The BGAs were obtained in Fe-(Al,Ga)-(P,C,B,Si), Fe-(Cr,Mo)-(C,B), Fe-(Zr,Hf,Nb,Ta)-B, Fe-Ln-B(Ln=lanthanide metal), Fe-B-Si-Nb and Fe-Nd-Al for Fe-based alloys, Co-(Ta,Mo)-B and Co-B-Si-Nb for Co-based alloys, Ni-Nb-(Ti,Zr)-(Co,Ni) for Ni-based alloys, and Cu-Ti-(Zr,Hf), Cu-Al-(Zr,Hf), Cu-Ti-(Zr,Hf)-(Ni,Co) and Cu-Al-(Zr,Hf)-(Ag,Pd) for Cu-based alloys. These BGAs exhibit useful properties of high mechanical strength, large elastic elongation and high corrosion resistance. In addition, Fe- and Co-based glassy alloys have good soft magnetic properties which cannot be obtained for amorphous and crystalline type magnetic alloys. The Feand Ni-based BGAs have already been used in some application fields. These LTM base BGAs are promising as new metallic engineering materials.
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Peng, Yuhan, Ge Zhou, Jinke Han, Jianlin Li, Haoyu Zhang, Siqian Zhang, Li Lin, Lijia Chen i Xue Cao. "Effect of Heat Treatment on the Corrosion Resistance of AlFeCoNiMo0.2 High-Entropy Alloy in NaCl and H2SO4 Solutions". Metals 13, nr 5 (26.04.2023): 849. http://dx.doi.org/10.3390/met13050849.
Pełny tekst źródłaStreszczenie:
The effects of casting and different heat treatment processes on the corrosion resistance of AlFeCoNiMo0.2 high-entropy alloy in 3.5% NaCl (mass fraction) and 0.5 mol/L H2SO4 solutions were investigated using dynamic potential polarization curves, SEM, XRD, XPS, and other test methods. The results show that in the Cl− environment, the cast alloy has the lowest corrosion current density and higher corrosion resistance compared to the annealed alloy. The elements Al and Mo are severely segregated in the crystal and in the grain boundaries, where galvanic corrosion occurs, and the Al-rich phase produces pitting corrosion in the crystal. The main components of its passive film are oxides of Al, Fe, Co, and Mo, and oxides and hydroxides of Ni. In the SO42− environment, the best corrosion resistance is achieved in the 900 °C annealed state of the alloy. Electrochemical test results show that the alloys all undergo secondary passivation, producing two successive product films to protect the metal matrix. Preferential corrosion areas are concentrated in the molybdenum-rich grain boundaries and nearby dendritic regions, reducing the corrosion resistance of the alloy. The main components of the passive film are oxides of Al and Mo; oxides of Fe, Co, Ni; and hydroxides. The Mo element in the passive film prevents the activated dissolution of Fe and produces the protective component MoO3, which inhibits the dissolution of the alloy and improves the stability of the passive film. The presence of Mo elements increases the selective dissolution of Fe, and the aggregation of Mo elements at grain boundaries after annealing weakens the corrosion resistance of the alloy and leads to the dissolution of the passive film. The main components of the passive film are oxides of Al and Mo; oxides of Fe, Co, Ni; and hydroxides.
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Sanin, Vitaliy V., Yury Yu Kaplansky, Maksym I. Aheiev, Evgeny A. Levashov, Mikhail I. Petrzhik, Marina Ya Bychkova, Andrey V. Samokhin, Andrey A. Fadeev i Vladimir N. Sanin. "Structure and Properties of Heat-Resistant Alloys NiAl–Cr–Co–X (X = La, Mo, Zr, Ta, Re) and Fabrication of Powders for Additive Manufacturing". Materials 14, nr 12 (8.06.2021): 3144. http://dx.doi.org/10.3390/ma14123144.
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The NiAl–Cr–Co–X alloys were produced by centrifugal self-propagating high-temperature synthesis (SHS) casting. The effects of dopants X = La, Mo, Zr, Ta, and Re on combustion, as well as the phase composition, structure, and properties of the resulting cast alloys, have been studied. The greatest improvement in overall properties was achieved when the alloys were co-doped with 15% Mo and 1.5% Re. By forming a ductile matrix, molybdenum enhanced strength characteristics up to the values σucs = 1604 ± 80 MPa, σys = 1520 ± 80 MPa, and εpd = 0.79%, while annealing at T = 1250 ℃ and t = 180 min improved strength characteristics to the following level: σucs = 1800 ± 80 MPa, σys = 1670 ± 80 MPa, and εpd = 1.58%. Rhenium modified the structure of the alloy and further improved its properties. The mechanical properties of the NiAl, ZrNi5, Ni0.92Ta0.08, (Al,Ta)Ni3, and Al(Re,Ni)3 phases were determined by nanoindentation. The three-level hierarchical structure of the NiAl–Cr–Co+15%Mo alloy was identified. The optimal plasma treatment regime was identified, and narrow-fraction powders (fraction 8–27 µm) characterized by 95% degree of spheroidization and the content of nanosized fraction <5% were obtained.
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Yao, Qiang, Tong Lu, Qiong Wang, Yan Wang i Yu Hong Zhu. "First-Principles Investigation of Phase Stability, Elastic and Thermodynamic Properties in L12 Co3(Al,Mo,Ta) Phase". Materials Science Forum 898 (czerwiec 2017): 438–45. http://dx.doi.org/10.4028/www.scientific.net/msf.898.438.
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First-principles calculations have been performed to investigate the phase stability, elastic, and thermodynamic properties of Co3(Al,Mo,Ta) with the L12 structure. Calculated elastic constants showed that Co3(Al,Mo,Ta) is mechanically stable and possesses intrinsic ductility. Young’s and shear moduli of polycrystalline Co3(Al,Mo,Ta) were calculated using the Voigt-Reuss-Hill approach. It was found that the shear and Young’s moduli of Co3(Al,Mo,Ta) were smaller than those of Co3(Al,W). States density indicated the existence of covalent-like bonding in Co3(Al,Mo,Ta). Temperature-dependent thermodynamic properties of Co3(Al,Mo,Ta) could be described satisfactorily using the Debye-Grüneisen approach, including entropy, enthalpy, heat capacity and linear thermal expansion coefficient, showing their significant temperature dependences. Furthermore the obtained data could be employed in the modeling of thermodynamic and mechanical properties of Co-based alloys to enable the design of high temperature alloys.
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Kitajima, Yuri, Shigenari Hayashi, Shigeharu Ukai i Toshio Narita. "The Effect of Additional Elements on Oxide Scale Evolution of Fe-20at.%Cr-10at.%Al Alloy at 900 °C in Air". Materials Science Forum 595-598 (wrzesień 2008): 1013–21. http://dx.doi.org/10.4028/www.scientific.net/msf.595-598.1013.
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The oxidation behavior of Fe-20at.%Cr-10at.%Al alloys with a small amount of an additional element such as W, Cu, Mn, Nb, Mo, Re, Co or Ti was investigated at 900 °C for up to 625hr. The fourth element addition to the FeCrAl alloy could be classified into two groups; elements (Mn, Nb, Ti) that are contained in the Al2O3 scale, and elements (W, Mo, Re, Co) which are not present in the scale. In the latter case, the elements (W, Cu) caused scale spallation. The rumpling of alloys with Mn, Nb or Ti was smaller than that of the other alloys. The surface of the alloy with Ti was the smooth. Pt marker experiments suggested that the Al2O3 scale formed on the alloy with Ti grew by inward diffusion of O, whilst the Al2O3 scale formed on the FeCrAl alloy grew by both outward diffusion of Al and inward diffusion of O. This different growth behavior due to the elements incorporated in the Al2O3 scale could have an effect on the surface rumpling behavior.
Rozprawy doktorskie na temat "Co-Mo-Al Alloys"
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OSTROWSKA, MARLENA. "Thermodynamic modelling and experimental validation of High Entropy Alloys containing Al, Co, Cr, Fe, Mo, Ni, Ta and W for high-temperature applications". Doctoral thesis, Università degli studi di Genova, 2021. http://hdl.handle.net/11567/1046937.
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The aim of the current project is to contribute to the design of novel High Entropy Alloys (HEAs) which meet targeted industrial needs, for instance the request for new high-temperature alloys.
HEAs attracted a lot of attention due to their promising high temperature mechanical performance. Taking into account a very wide range of alloys that fall into this group of materials, using only experimental investigations would be insufficient in finding new compositions with attractive properties.
The objective is achieved by thermodynamic modelling of the Al-Co-Cr-Fe-Mo-Ni-Ta-W system, through the CALPHAD method, in order to predict the best candidate elements and compositions which can give the required structure.
The reliable and self-consistent database is obtained by assessing several important ternary systems and by adopting published assessments, if they were compatible with the models selected in this work.
The reliability of the database is verified with experimental measurements performed during this work regarding the reference system Al-Co-Cr-Fe-Ni, as well as the critically selected published experimental data regarding several other multicomponent systems containing Mo and W.
The synergy between modelling and experimental validation produce a highly reliable thermodynamic database which allows to screen and quickly identify high performance compositions, with a significant reduction in time and costs with respect to traditional trial and error experiments.
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Royer, Agnès. "Evolutions thermique et mécanique de la microstructure de superalliages monocristallins étudiées par diffusion centrale et diffraction (neutrons, rayons [gamma])". Grenoble 1, 1993. http://www.theses.fr/1993GRE10097.
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Les experiences de diffraction et de diffusion des rayonnements gamma et neutron nous ont permis d'etudier la microstructure du superalliage monocristallin am1 ainsi que son evolution en fonction de la temperature. Ces experiences ont pour la plupart ete realisees in situ en temperature et nos resultats qui sont relatifs a un grand nombre de precipites, ne sont pas sensibles aux heterogeneites locales de composition chimique. Nous avons analyse la morphologie des precipites gamma prime a l'aide d'experiences de diffusion aux petits angles des neutrons, au cours des phenomenes de precipitation et de coalescence des precipites gamma prime. La remise en solution de ces precipites a ete etudiee par diffraction neutron jusqu'a complete dissolution. Afin de mieux comprendre les mecanismes qui regissent l'evolution de la morphologie des precipites, nous avons etudie en temperature differents parametres microstructuraux. Par diffraction gamma, nous avons mis en evidence une distorsion tetragonale au sein du materiau et le desaccord parametrique entre les deux phases a pu etre mesure par diffraction neutrons a grands angles de bragg. La synthese des resultats obtenus au cours de ces differentes experiences, nous a permis d'etablir un modele qui prevoit l'evolution des parametres de maille des phases gamma et gamma prime en fonction de la temperature lors de recuits thermiques et sous contrainte
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Makineni, Surendra Kumar. "Improvement of High Temperature Strength of Al and Co Alloy by L12 Type Coherent Precipitates". Thesis, 2015. https://etd.iisc.ac.in/handle/2005/4348.
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The present work aims at developing a new class of high temperature alloys based on ordered
intermetallic compound that forms coherently with the matrix during solid state transformation.
The chosen intermetallics have L12 ordered structure, which is a derivative of fcc unit cell.
Most popular example of this fcc derivative is Ni3Al that is critical in developing high strength
at high temperatures (~900°C) in commercially successful Ni based superalloys. Similar
ordered structures form either in stable or metastable form can act as a main strengthening
constituent in Al and Co matrices.
For example Al3Sc, Al3Zr, Al3Hf can be dispersed in fcc Al matrix that are stable at
temperatures ~ 400°C due to very low diffusivity of transition metals (Sc, Zr, Hf etc.) in the
matrix. However, due to low solid solubility of these transition metals, the obtained volume
fraction of these precipitates in the matrix is not sufficient to provide adequate room
temperature strength.
In fcc Co matrix, stable Co3Ti phase with L12 ordered structure forms with cuboidal
morphology. However, besides having lower melting point, the precipitates have large misfit
that lowers thermal stability at high temperatures. Recently, addition of Al and W with a proper
ratio in Co is reported to lead the formation of metastable Co3(Al,W) L12 ordered phase in fcc
α-Co matrix. This provides significant strength at high temperatures (~ 900°C). The main
drawback for these alloys is their high densities (9.6 to 10.5 gm.cm-3) due to the requirement of
compulsory addition of W (~ 15 to 25 wt%) for stabilising the ordered phase.
In the present work, these problems are overcome leading to the development of new class of
Al and Co alloys. The thesis is organized in three parts. In the first part, the principles of
strengthening that can be optimized to develop newer high temperature high strength alloys are
reviewed. The ordered L12 structure, which is the mainstay of the current effort of new alloy
development, is elaborated. In the second part we present the results of our effort to the
development a new class of high strength high temperature Al alloys. A new approach has been
adopted to get a microstructure that contains both high temperature stable and room
temperature strengthening precipitates. This has been illustrated by two Al rich compositions,
Al-2Cu-0.1Nb-0.15Zr and Al-2Cu-0.1Hf-0.15Zr (at% unless stated otherwise). Addition of
Nb/Zr or Hf/Zr in Al alloys leads to the formation of high temperature stable L12 ordered
spherical coherent precipitates in the fcc Al matrix. Cu addition gives room temperature
strengthening θ’ and θ” precipitates. The arc melted alloys were chill cast (suction cast) in the
form of 3 mm rods followed by a novel three stage heat treatment process, as shown below.
In the case of Al-2Cu-0.1Nb-0.15Zr alloy, the chill cast structure consists of Cu rich phase at
the boundaries along the α-Al dendrites while Zr and Nb partition inside the α-Al dendrites.
Aging at 400°C leads to an increase in the hardness of the cast alloy due to the precipitation of
coherent L12 ordered Al3(Zr,Nb) spherical precipitates (~5nm) in the α-Al dendrites. Zr
strongly partitions to the L12 ordered precipitate relative to the matrix. Nb exhibits weak
partitioning in the precipitate. Further solutionising was optimized at 535°C for 30 minutes
such that the segregation of Cu in the chill cast samples can be eliminated. The WDS mapping
shows that Cu dissolved uniformly in the α-matrix while the Zr/Nb enriched α-Al dendrites are
still present. The L12 ordered precipitates are mostly found in these Zr/Nb enriched dendrites
formed during solidification. The precipitates sizes are finer (~5 nm) in dendrites and larger in
the interdendritic region. The Nb partitioning increases in the ordered L12 precipitates relative
to the matrix after solutionising. On aging at 190°C, fine θ” precipitates nucleate on prior
Al3(Zr,Nb) precipitates present in α-Al dendrites while the interdendritic regions contain
coarser θ’ nucleated on larger size L12 precipitates. The θ”/θ’ are much finer and higher in
number density for the quaternary alloy compared to binary Al-2Cu alloy subjected to
conventional heat treatment. The quaternary alloy show higher peak hardness of 1500 ± 8 MPa
after 5 hours of aging at 190°C compared to binary Al-2Cu alloy with peak hardness of 1260 ±
11 MPa.
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Su, Ying Chi, i 蘇穎奇. "Study on Improving the Mechanical Properties and Dual Phase (BCC + σ) of Al-Co-Cr-Fe-Mo-Ni High Entropy Alloys by Alloy Design". Thesis, 2015. http://ndltd.ncl.edu.tw/handle/y7qnc9.
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胡雅惠. "Evolution of microstructure and properties in Cu-Ni-Al-Co-Cr-Fe-Ti-Mo alloys with multi-principal elements during mechanical alloying". Thesis, 2004. http://ndltd.ncl.edu.tw/handle/69744200954601490438.
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許經佑. "Effects of element content on the microstructure and mechanical properties of Al-Co-Cr-Fe-Mo-Ni high-entropy alloy system". Thesis, 2009. http://ndltd.ncl.edu.tw/handle/39070000261251445282.
Pełny tekst źródłaKsiążki na temat "Co-Mo-Al Alloys"
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A, Barrett Charles, i United States. National Aeronautics and Space Administration., red. The effect of Cr, Co, Al, Mo, and Ta on a series of cast Ni-base superalloys on the stability of an aluminide coating during cyclic oxidation in Mach 0.3 burner rig. [Washington, D.C.]: National Aeronautics and Space Administration, 1986.
Znajdź pełny tekst źródłaStreszczenia konferencji na temat "Co-Mo-Al Alloys"
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Pint, Bruce A. "Simulated Fireside Corrosion of Ni-Base Alloys in Oxy-Fired Conditions at 700°–800°C". W ASME 2014 Symposium on Elevated Temperature Application of Materials for Fossil, Nuclear, and Petrochemical Industries. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/etam2014-1023.
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One future objective for coal-fired power generation is to develop advanced ultrasupercritical (A-USC) boilers that incorporate oxy-firing to facilitate carbon capture. The steam condition goals of 760°C/34.5 MPa will require major materials changes throughout the boiler, including Ni-base alloys in the hottest sections. Solution hardened alloys such as 740 and 282 are needed to meet the strength requirements for 760°C. In previous work, little difference in corrosion rate was found between air- and oxy-firing for alloy 740 at 600°–800°C so laboratory testing focused on the “worst case” oxy-firing conditions with higher CO2, H2O and SO2 than expected with air-firing. Model alloys were made to investigate the roles of Cr, Al, Ti, Co and Mo on the fireside corrosion behavior. Exposures conducted for 500h at 700° and 800°C found that Al and Ti additions typically reduced the extent of attack under these conditions. As expected, the alloy Cr content had a substantial effect between 18 and 22%. Additions of 4% and 8%Mo to Ni-20Cr-(0-20)Co alloys increased the metal loss at 800°C and Ni-20Cr-20Co-(0-8%)Mo showed the highest attack at 700°C. The much higher attack of alloy 282 at 800°C can likely be attributed to its lower Cr content compared to alloy 740, which was developed to have excellent fireside corrosion resistance. Paper published with permission.
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Robertson, J. R. "Continued Developments in the Characteristics of HAYNES® 282® Alloy for Use in A-USC Applications". W ASME 2018 Symposium on Elevated Temperature Application of Materials for Fossil, Nuclear, and Petrochemical Industries. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/etam2018-6745.
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Increasing global demands for energy are spurring research efforts to improve the efficiency of fossil power plants while simultaneously reducing the emission of greenhouse gases. Current research reveals that a power plant’s efficiency increases when it is operated at Advanced Ultra Super Critical (A-USC) temperatures and pressures. These operating conditions require some plant components to be made from nickel-based superalloys. Previous research has established HAYNES® 282® alloy1 (UNS N07208), a Ni-Cr-Co-Mo-Ti-Al precipitation hardenable alloy, as a viable choice for A-USC applications. For such components, current interest is focused on the development of a single step age hardening treatment. An earlier paper presented the mechanical properties of an 8-hour single step age hardening heat treatment at 800°C (1472°F)/8 hr/AC. This paper will review preliminary results of a shorter single age treatment: 800°C (1472°F)/4 hr/AC.
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Tsakalakos, Loucas, Lauraine Denault, Michael Larsen, Mohamed Rahmane, Yan Gao, Joleyn Balch i Paul Wilson. "Mo2C Nanowires and Ribbons on Si via Two-Step Vapor Phase Growth". W ASME 2004 3rd Integrated Nanosystems Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/nano2004-46098.
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Transition metal carbides are an interesting class of electronic materials owing to their high electrical conductivity at room temperature, which is only slightly lower than that of their constituent transition metal elements. For example, the room temperature electrical resistivity of bulk Mo2C is ∼70 μΩ-cm compared to that of Mo (4.85 μΩ-cm), whereas that of NbC is ∼50 μΩ-cm as compared to 15.2 μΩ-cm for Nb. Indeed, the temperature dependent resistivity of many transition metal carbides suggests metallic-like conduction. Furthermore, certain transition metal carbides are known to become superconducting, with transition temperatures ranging from 1.15 °K for TiC1−x to 14 °K for NbC. [1] They are also able to withstand high temperatures and are chemically stable. Initial synthesis of metal carbide nanorods was demonstrated using the carbon nanotube (CNT) confined reaction mechanism by Lieber and co-workers [2] and subsequent superconducting behavior was shown by Fukunaga et al. [3]. Vapor-liquid-solid growth was employed by Johnson et al. [4] to synthesize micron-sized carbide whiskers. Here, we have successfully synthesized Mo2C nanorods and ribbons on Si substrates using a novel two-step catalytic approach, which allows for synthesis of such high temperature nanostructures at manufacturable temperatures (≤ 1000 °C) and time scales (≤ 60 min). In the first step we utilize a catalytic vapor phase process to grow Mo and/or molybdenum oxide nanostructures, which are subsequently carburized in situ to form the desired Mo2C nanostructures. Unlike true VLS growth of carbides, in which high temperature (≤ 1100–1200 °C) is required to adequately dissolve carbon into the catalyst particles, our strategy is to react the nanostructures along their entire length with a carbon vapor source after creating the oxide/metal nanostructures, which for Mo2C can be achieved at relatively low temperatures. (≤ 1000 °C). The nanorods and ribbons are polycrystalline, with a mean grain size of 20–50 nm and 50–150 nm, respectively. We hypothesize that the growth mechanism is a complex mixture of VLS, VSS, and auto-catalytic growth, in which molten catalyst nanoparticles enter a three phase region once the metal precursor is supplied. The growth then presumably continues via a vapor-solid-solid process and is possible assisted by the presence of various molybdenum oxide species on the surface. Initial single nanowire electrical measurements yield a higher resistivity than in the bulk, which is attributed to the fine grain sizes and/or the presence of an oxide layer. A discussion of the growth mechanism will be presented along with issues relating to single nanowire device fabrication and control of nanowire orientation.