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K Chattopadhyay - One of the best experts on this subject based on the ideXlab platform.
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on the effect of w addition on microstructural evolution and γ precipitate coarsening in a co 30ni 10al 5mo 2ta 2ti alloy
Materialia, 2020Co-Authors: Surendra Kumar Makineni, Nithin Baler, Prafull Pandey, Dhanalakshmi Palanisamy, G Phanikumar, K ChattopadhyayAbstract:Abstract The effect of replacement of molybdenum with small amount of tungsten on the stability of cobalt based Superalloys of Co–Ni–Mo–Al–Ta–Ti class has been presented. A small addition of tungsten (W) in Co–30Ni–(5-x)Mo–10Al–2Ta–2Ti–2W alloys stabilizes the cuboidal morphology of precipitates and increases the γ′ volume fraction. A 2 at% addition of W causes an increase of 60 °C in solvus temperature of the base superalloy to reach a value of 1130 °C with a slight increase of mass density to 8.79 g/cc. Beside partitioning into γ′, W also shifts the partitioning preference of Mo from the γ′ phase in 0W alloy to that of equal partitioning in both γ and γ’ phases in 2W alloy. An interfacial confinement of Mo atoms could be observed at the γ/γ′ interfaces that reduces interface energy leading to enhanced microstructural stability. The experimentally determined temporal evolution of average precipitate size in the 2W alloy at the temperatures of 800, 900 and 950 °C suggests a matrix diffusion limited coarsening kinetics. The estimated coarsening rate constant at 900 °C follows a quasi-steady state model and is comparable to those observed for W and Re containing Co-based Superalloys. The activation energy for γ′ precipitate coarsening is estimated to be 258 ± 6 kJ/mole, which is comparable to the Mo diffusion in the γ-Co matrix suggesting Mo diffusion still controls the precipitate coarsening in the 2W alloy.
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a new tungsten free γ γ co al mo nb based superalloy
Scripta Materialia, 2015Co-Authors: Surendra Kumar Makineni, B Nithin, K ChattopadhyayAbstract:We present the first report of a tungsten-free Cobalt-Based superalloy having a composition Co–10Al–5Mo–2Nb. The alloy is strengthened by cuboidal precipitates of metastable Co3(Al,Mo,Nb) distributed throughout the microstructure. The precipitates are coherent with the face-centred cubic γ-Co matrix and possess ordered L12 structure. The microstructure is identical to the popular γ–γ’ type nickel-based Superalloys and that of recently reported Co–Al–W-based alloys. Being tungsten free, the reported alloy has higher specific proof stress compared to existing Cobalt-Based Superalloys.
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synthesis of a new tungsten free γ γ cobalt based superalloy by tuning alloying additions
Acta Materialia, 2015Co-Authors: Surendra Kumar Makineni, B Nithin, K ChattopadhyayAbstract:Abstract The paper presents the synthesis of a new class of γ–γ′ Cobalt-Based superalloy that is free of tungsten as an alloying addition. It has much lower density and higher specific strength than the existing Cobalt-Based Superalloys. The current Superalloys have a base composition of Co–10Al and are further tuned by the addition of a binary combination of molybdenum and niobium, with the optimum composition of Co–10Al–5Mo–2Nb. The solvus temperature of the alloy (866 °C) can be further enhanced above 950 °C by the addition of Ni to give the form Co– x Ni–10Al–5Mo–2Nb, where x can be from 0 to 30 at.%. After heat treatment, these alloys exhibit a duplex microstructure with coherent cuboidal L1 2 -ordered precipitates (γ′) throughout the face-centred cubic matrix (γ), yielding a microstructure that is very similar to nickel-based Superalloys as well as recently developed Co–Al–W-based alloys. We show that the stability of the γ′ phase improves significantly with the nickel addition, which can be attributed to the increase in solvus temperature. A very high specific 0.2% proof stress of 94.3 MPa g −1 cm −3 at room temperature and 63.8 MPa g −1 cm −3 at 870 °C were obtained for alloy Co–30Ni–10Al–5Mo–2Nb. The remarkably high specific strength of these alloys makes this class of alloy a promising material for use at high temperature, including gas turbine applications.
Surendra Kumar Makineni - One of the best experts on this subject based on the ideXlab platform.
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on the effect of w addition on microstructural evolution and γ precipitate coarsening in a co 30ni 10al 5mo 2ta 2ti alloy
Materialia, 2020Co-Authors: Surendra Kumar Makineni, Nithin Baler, Prafull Pandey, Dhanalakshmi Palanisamy, G Phanikumar, K ChattopadhyayAbstract:Abstract The effect of replacement of molybdenum with small amount of tungsten on the stability of cobalt based Superalloys of Co–Ni–Mo–Al–Ta–Ti class has been presented. A small addition of tungsten (W) in Co–30Ni–(5-x)Mo–10Al–2Ta–2Ti–2W alloys stabilizes the cuboidal morphology of precipitates and increases the γ′ volume fraction. A 2 at% addition of W causes an increase of 60 °C in solvus temperature of the base superalloy to reach a value of 1130 °C with a slight increase of mass density to 8.79 g/cc. Beside partitioning into γ′, W also shifts the partitioning preference of Mo from the γ′ phase in 0W alloy to that of equal partitioning in both γ and γ’ phases in 2W alloy. An interfacial confinement of Mo atoms could be observed at the γ/γ′ interfaces that reduces interface energy leading to enhanced microstructural stability. The experimentally determined temporal evolution of average precipitate size in the 2W alloy at the temperatures of 800, 900 and 950 °C suggests a matrix diffusion limited coarsening kinetics. The estimated coarsening rate constant at 900 °C follows a quasi-steady state model and is comparable to those observed for W and Re containing Co-based Superalloys. The activation energy for γ′ precipitate coarsening is estimated to be 258 ± 6 kJ/mole, which is comparable to the Mo diffusion in the γ-Co matrix suggesting Mo diffusion still controls the precipitate coarsening in the 2W alloy.
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a new tungsten free γ γ co al mo nb based superalloy
Scripta Materialia, 2015Co-Authors: Surendra Kumar Makineni, B Nithin, K ChattopadhyayAbstract:We present the first report of a tungsten-free Cobalt-Based superalloy having a composition Co–10Al–5Mo–2Nb. The alloy is strengthened by cuboidal precipitates of metastable Co3(Al,Mo,Nb) distributed throughout the microstructure. The precipitates are coherent with the face-centred cubic γ-Co matrix and possess ordered L12 structure. The microstructure is identical to the popular γ–γ’ type nickel-based Superalloys and that of recently reported Co–Al–W-based alloys. Being tungsten free, the reported alloy has higher specific proof stress compared to existing Cobalt-Based Superalloys.
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synthesis of a new tungsten free γ γ cobalt based superalloy by tuning alloying additions
Acta Materialia, 2015Co-Authors: Surendra Kumar Makineni, B Nithin, K ChattopadhyayAbstract:Abstract The paper presents the synthesis of a new class of γ–γ′ Cobalt-Based superalloy that is free of tungsten as an alloying addition. It has much lower density and higher specific strength than the existing Cobalt-Based Superalloys. The current Superalloys have a base composition of Co–10Al and are further tuned by the addition of a binary combination of molybdenum and niobium, with the optimum composition of Co–10Al–5Mo–2Nb. The solvus temperature of the alloy (866 °C) can be further enhanced above 950 °C by the addition of Ni to give the form Co– x Ni–10Al–5Mo–2Nb, where x can be from 0 to 30 at.%. After heat treatment, these alloys exhibit a duplex microstructure with coherent cuboidal L1 2 -ordered precipitates (γ′) throughout the face-centred cubic matrix (γ), yielding a microstructure that is very similar to nickel-based Superalloys as well as recently developed Co–Al–W-based alloys. We show that the stability of the γ′ phase improves significantly with the nickel addition, which can be attributed to the increase in solvus temperature. A very high specific 0.2% proof stress of 94.3 MPa g −1 cm −3 at room temperature and 63.8 MPa g −1 cm −3 at 870 °C were obtained for alloy Co–30Ni–10Al–5Mo–2Nb. The remarkably high specific strength of these alloys makes this class of alloy a promising material for use at high temperature, including gas turbine applications.
B Nithin - One of the best experts on this subject based on the ideXlab platform.
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a new tungsten free γ γ co al mo nb based superalloy
Scripta Materialia, 2015Co-Authors: Surendra Kumar Makineni, B Nithin, K ChattopadhyayAbstract:We present the first report of a tungsten-free Cobalt-Based superalloy having a composition Co–10Al–5Mo–2Nb. The alloy is strengthened by cuboidal precipitates of metastable Co3(Al,Mo,Nb) distributed throughout the microstructure. The precipitates are coherent with the face-centred cubic γ-Co matrix and possess ordered L12 structure. The microstructure is identical to the popular γ–γ’ type nickel-based Superalloys and that of recently reported Co–Al–W-based alloys. Being tungsten free, the reported alloy has higher specific proof stress compared to existing Cobalt-Based Superalloys.
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synthesis of a new tungsten free γ γ cobalt based superalloy by tuning alloying additions
Acta Materialia, 2015Co-Authors: Surendra Kumar Makineni, B Nithin, K ChattopadhyayAbstract:Abstract The paper presents the synthesis of a new class of γ–γ′ Cobalt-Based superalloy that is free of tungsten as an alloying addition. It has much lower density and higher specific strength than the existing Cobalt-Based Superalloys. The current Superalloys have a base composition of Co–10Al and are further tuned by the addition of a binary combination of molybdenum and niobium, with the optimum composition of Co–10Al–5Mo–2Nb. The solvus temperature of the alloy (866 °C) can be further enhanced above 950 °C by the addition of Ni to give the form Co– x Ni–10Al–5Mo–2Nb, where x can be from 0 to 30 at.%. After heat treatment, these alloys exhibit a duplex microstructure with coherent cuboidal L1 2 -ordered precipitates (γ′) throughout the face-centred cubic matrix (γ), yielding a microstructure that is very similar to nickel-based Superalloys as well as recently developed Co–Al–W-based alloys. We show that the stability of the γ′ phase improves significantly with the nickel addition, which can be attributed to the increase in solvus temperature. A very high specific 0.2% proof stress of 94.3 MPa g −1 cm −3 at room temperature and 63.8 MPa g −1 cm −3 at 870 °C were obtained for alloy Co–30Ni–10Al–5Mo–2Nb. The remarkably high specific strength of these alloys makes this class of alloy a promising material for use at high temperature, including gas turbine applications.
Akihiko Chiba - One of the best experts on this subject based on the ideXlab platform.
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regulating the coarsening of the gamma prime phase in Superalloys
Npg Asia Materials, 2015Co-Authors: Huakang Bian, Yuichiro Koizumi, Zhongchang Wang, Mingwei Chen, Kenta Yamanaka, Akihiko ChibaAbstract:The properties of Superalloys are typically deteriorated by the coarsening of the nano-sized γ′ phase, which is the primary strengthening component at high temperatures. Stabilizing the γ′ phase represents one of the key challenges in developing next-generation Superalloys. Herein, we fabricate a cobalt-nickel-based superalloy with a nanoscale coherent γ′ phase, (Ni,Co)3(Al,Ti,Nb), which is isolated by stacking-fault ribbons in the alloy matrix as a result of the Suzuki segregation of alloying atoms. Additionally, we demonstrate that this new nanostructure can slow down the coarsening of the γ′ phase at high temperatures. As a result, the cobalt-nickel-based superalloy displays considerably high tensile yield points, exceeding 1650 MPa at room temperature and 1250 MPa at 973 K, which are markedly higher than those of the commonly used nickel- and Cobalt-Based Superalloys. This study thereby paves a new path for developing Superalloys with exceptional mechanical performance and thermal stability. By using a novel nanostructure, a team has made a Cobalt-Based superalloy with a high tensile yield point whose γ' phase resists coarsening. Coarsening of the nanoscale γ' phase of Superalloys — the process by which large particles grow at the expense of smaller ones — tends to degrade the properties of Superalloys since the γ' phase is the main strengthening component at high temperatures. By isolating the γ' phase through forming stacking-fault ribbons in the alloy matrix via Suzuki segregation of the alloying atoms, Yunping Li of Central South University in China and collaborators at Tohoku University in Japan realized a cobalt-nickel-based superalloy with a tensile yield point of 1,650 megapascals at room temperature (1,250 megapascals at 973 kelvin). They consider this method to be promising for realizing Superalloys with superior mechanical properties and thermal stability. A large number of multilayered stacking faults are detected along {111} planes during aging (arrows in a) of present superalloy. Every γ′ phase particle is isolated by multilayered stacking-fault ribbons and grows slightly. The coarsening rate of the γ′ phase decreases significantly after plastic deformation, implying that the formation of multilayered stacking-fault ribbons as a consequence of Suzuki segregation can obviously retard the coarsening of γ′ phase in this novel alloy.
Qi Yang - One of the best experts on this subject based on the ideXlab platform.
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Wear resistant carbon fiber reinforced Stellite alloy composites
Materials & Design, 2014Co-Authors: Alireza Khoddamzadeh, Rong Liu, Ming Liang, Qi YangAbstract:Abstract Stellite alloys are a family of Cobalt-Based Superalloys that are the main engineering materials used for severe corrosion, wear and high temperature environments. These alloys are strengthened by various carbides. However, the presence of carbides can cause many problems although they are main agents for wear resistance. This research attempts to develop a class of novel composite materials which substitute carbon of Stellite alloys with carbon fiber, aiming to minimize the disadvantageous effects of carbides in the alloys. Two types of carbon fiber, plain carbon fiber and nickel-coated carbon fiber, are employed in the composites. The new materials are fabricated using hot isostatic pressing (HIP) technique. The microstructures of these composites are analyzed to investigate if any carbides are induced due to incorporating carbon fibers. The tribological properties of these new composites are characterized on a pin-on-disk tribometer. The experimental results show that the developed composites exhibit better wear resistance than that of medium-carbon Stellite alloys and comparable wear resistance to that of high-carbon Stellite alloys.