The Experts below are selected from a list of 138 Experts worldwide ranked by ideXlab platform
O N Senkov - One of the best experts on this subject based on the ideXlab platform.
-
calphad aided development of quaternary multi principal element Refractory Alloys based on nbtizr
Journal of Alloys and Compounds, 2019Co-Authors: O N Senkov, C Zhang, A L Pilchak, E J Payton, C Woodward, F ZhangAbstract:Abstract Equilibrium phase diagrams for ten MeX(NbTiZr)100-X alloy systems, where Me is Al, Cr, Fe, Hf, Mo, Re, Si, Ta, V or W and X ranges from 0 to 25 at% were calculated using the PanNb2018a database recently developed by CompuTherm, LLC. By the type of phases and sequence of formation, these alloy systems can be divided into two groups. The first group of quaternary Alloys, containing Al, Hf, Mo, Ta, or V has a single-phase BCC region below the solidus line over the entire X range and can be considered as potential candidates for the development of single-phase high entropy Alloys. The second group consists of the quaternary alloy systems in which the fourth element (Cr, Fe, Re, Si or W) has limited solubility in BCC NbTiZr, which leads to the formation of an additional phase below the solidus and above the solubility limit. These quaternary alloy systems can be used for the development of precipitation or dispersoid strengthened complex concentrated Alloys. To verify CALPHAD calculations three representative Alloys, Cr10Nb30Ti30Zr30, Ta10Nb30Ti30Zr30 and Re10Nb30Ti30Zr30, were prepared by arc melting. The alloy densities were 6.56, 7.81 and 7.85 g/cm3, respectively. The phase compositions of the produced Alloys agreed satisfactorily with CALPHAD calculations. Mechanical properties were also studied and compared with those of NbTiZr. At room temperature (RT) all the Alloys showed high hardness exceeding 350 Hv and high compression yield stress exceeding 1000 MPa. RT compression ductility of Re and Ta containing Alloys was above 50%, but Cr-containing alloy showed low ductility of 5%. With an increase in temperature ≥800 °C, compression strength decreased more rapidly for the Cr-containing alloy, which at 1200 °C became softer than NbTiZr. The least temperature dependence of the strength was observed for the Ta-containing alloy, which became the strongest at 1200 °C.
-
development and exploration of Refractory high entropy Alloys a review
Journal of Materials Research, 2018Co-Authors: O N Senkov, K J Chaput, D B Miracle, Jeanphilippe CouzinieAbstract:Open literature publications, in the period from 2010 to the end of January 2018, on Refractory high entropy Alloys (RHEAs) and Refractory complex concentrated Alloys (RCCAs) are reviewed. While RHEAs, by original definition, are Alloys consisting of five or more principal elements with the concentration of each of these elements between 5 and 35 at.%, RCCAs can contain three or more principal elements and the element concentration can be greater than 35%. The 151 reported RHEAs/RCCAs are analyzed based on their composition, processing methods, microstructures, and phases. Mechanical properties, strengthening and deformation mechanisms, oxidation, and corrosion behavior, as well as tribology, of RHEA/RCCAs are summarized. Unique properties of some of these Alloys make them promising candidates for high temperature applications beyond Ni-based superAlloys and/or conventional Refractory Alloys. Methods of development and exploration, future directions of research and development, and potential applications of RHEAs are discussed.
-
high temperature oxidation behaviors of equimolar nbtizrv and nbtizrcr Refractory complex concentrated Alloys rccas
Journal of Alloys and Compounds, 2017Co-Authors: T M Butler, K J Chaput, J R Dietrich, O N SenkovAbstract:Abstract Refractory complex concentrated Alloys (RCCAs) represent an emerging class of materials that have displayed significant potential for increased mechanical performance at extreme temperatures over conventional Refractory Alloys and Ni-base superAlloys. While limited work has been conducted in this area, several RCCAs have shown remarkable levels of oxidation resistance in comparison to the majority of uncoated commercial Refractory Alloys. However, the oxidation mechanisms in these types of Alloys have not been well understood. This study aims to develop the foundation for understanding RCCA oxidation mechanisms through the systematic evaluation of NbTiZrV and NbTiZrCr, which display vastly different oxidation behaviors. In both cases, the predominant mechanism appeared to be internal oxidation, where a mixture of simple and complex oxides was observed after prolonged oxidation times. This resulted in extended linear oxidation kinetics for the NbTiZrV alloy and linear to near-parabolic oxidation kinetics for the NbTiZrCr alloy. Under this mindset, novel design strategies for promoting increased oxidation resistance in both RCCAs and dilute Refractory Alloys based on sluggish complex oxides are proposed.
-
microstructure and properties of aluminum containing Refractory high entropy Alloys
JOM, 2014Co-Authors: O N Senkov, C Woodward, D B MiracleAbstract:A new metallurgical strategy, high-entropy alloying (HEA), was used to explore new composition and phase spaces in the development of new Refractory Alloys with reduced densities and improved properties. Combining Mo, Ta, and Hf with “low-density” Refractory elements (Nb, V, and Zr) and with Ti and Al produced six new Refractory HEAs with densities ranging from 6.9 g/cm3 to 9.1 g/cm3. Three Alloys have single-phase disordered body-centered cubic (bcc) crystal structures and three other Alloys contain two bcc nanophases with very close lattice parameters. The Alloys have high hardness, in the range from H v = 4.0 GPa to 5.8 GPa, and compression yield strength, σ 0.2 = 1280 MPa to 2035 MPa, depending on the composition. Some of these Refractory HEAs show considerably improved high temperature strengths relative to advanced Ni-based superAlloys. Compressive ductility of all the Alloys is limited at room temperature, but it improves significantly at 800°C and 1000°C.
A J Clarke - One of the best experts on this subject based on the ideXlab platform.
-
solid solution strengthening in Refractory high entropy Alloys
Acta Materialia, 2019Co-Authors: Francisco Gil Coury, M J Kaufman, A J ClarkeAbstract:Abstract Compression stress-strain curves of a number of Refractory high entropy Alloys (RHEAs) were generated at temperatures ranging from room temperature to 1000 °C. It is shown that solid-solution strengthening in these Alloys has both an athermal and a thermal component. Results from mechanical testing are combined with literature data to develop solid-solution strengthening models for both components that incorporate the particularities of single-phase body centered cubic (BCC) materials. The athermal component is affected by a combination of atomic size mismatch and elastic modulus mismatch, which depend upon average values from each alloy, thereby allowing this component to be estimated in a high-throughput fashion. On the other hand, the thermally-activated yield stress component does not correlate with any parameter that can be calculated by averaging pure elemental atomic properties and it is observed to be larger than the values found for pure BCC Refractory metals and their dilute Alloys. Overall, RHEAs are found to have larger thermal and athermal yield stress components compared to pure or conventional Refractory Alloys, which explains their relatively high strengths at room temperature.
-
phase equilibria mechanical properties and design of quaternary Refractory high entropy Alloys
Materials & Design, 2018Co-Authors: Francisco Gil Coury, T M Butler, K J Chaput, Alec Saville, John Copley, John Foltz, Paul Mason, Kester D Clarke, M J Kaufman, A J ClarkeAbstract:Abstract Refractory high entropy Alloys (RHEAs) are candidates for replacing conventional Refractory Alloys. In this work, twelve new RHEAs were selected and produced. The phases present in the as-cast and heat-treated conditions were characterized and compared with CALPHAD simulations and empirical parameters. Here we propose a new interpretation for the two widely used δ and Ω empirical parameters. In this work, they are shown to be inaccurate when applied to a large group of RHEAs, but can be a powerful alloy design tool if applied on specific subsystems of Alloys. Experimentally, chromium-containing Alloys are shown to form Laves phases, especially when the lattice distortion (δ) is high, while aluminum-containing Alloys are shown to form the A15 phase upon heat-treatment, due to their highly negative enthalpy of mixing (ΔHmix). In addition to microstructural characterization, mechanical properties of these Alloys via hardness testing were assessed. A poor correlation was observed between the hardness and the atomic size and elastic modulus mismatch in these single-phase BCC RHEAs, suggesting that core structure of the screw dislocations is a crucial parameter in understanding the strength of these Alloys.
Francisco Gil Coury - One of the best experts on this subject based on the ideXlab platform.
-
solid solution strengthening in Refractory high entropy Alloys
Acta Materialia, 2019Co-Authors: Francisco Gil Coury, M J Kaufman, A J ClarkeAbstract:Abstract Compression stress-strain curves of a number of Refractory high entropy Alloys (RHEAs) were generated at temperatures ranging from room temperature to 1000 °C. It is shown that solid-solution strengthening in these Alloys has both an athermal and a thermal component. Results from mechanical testing are combined with literature data to develop solid-solution strengthening models for both components that incorporate the particularities of single-phase body centered cubic (BCC) materials. The athermal component is affected by a combination of atomic size mismatch and elastic modulus mismatch, which depend upon average values from each alloy, thereby allowing this component to be estimated in a high-throughput fashion. On the other hand, the thermally-activated yield stress component does not correlate with any parameter that can be calculated by averaging pure elemental atomic properties and it is observed to be larger than the values found for pure BCC Refractory metals and their dilute Alloys. Overall, RHEAs are found to have larger thermal and athermal yield stress components compared to pure or conventional Refractory Alloys, which explains their relatively high strengths at room temperature.
-
phase equilibria mechanical properties and design of quaternary Refractory high entropy Alloys
Materials & Design, 2018Co-Authors: Francisco Gil Coury, T M Butler, K J Chaput, Alec Saville, John Copley, John Foltz, Paul Mason, Kester D Clarke, M J Kaufman, A J ClarkeAbstract:Abstract Refractory high entropy Alloys (RHEAs) are candidates for replacing conventional Refractory Alloys. In this work, twelve new RHEAs were selected and produced. The phases present in the as-cast and heat-treated conditions were characterized and compared with CALPHAD simulations and empirical parameters. Here we propose a new interpretation for the two widely used δ and Ω empirical parameters. In this work, they are shown to be inaccurate when applied to a large group of RHEAs, but can be a powerful alloy design tool if applied on specific subsystems of Alloys. Experimentally, chromium-containing Alloys are shown to form Laves phases, especially when the lattice distortion (δ) is high, while aluminum-containing Alloys are shown to form the A15 phase upon heat-treatment, due to their highly negative enthalpy of mixing (ΔHmix). In addition to microstructural characterization, mechanical properties of these Alloys via hardness testing were assessed. A poor correlation was observed between the hardness and the atomic size and elastic modulus mismatch in these single-phase BCC RHEAs, suggesting that core structure of the screw dislocations is a crucial parameter in understanding the strength of these Alloys.
K J Chaput - One of the best experts on this subject based on the ideXlab platform.
-
development and exploration of Refractory high entropy Alloys a review
Journal of Materials Research, 2018Co-Authors: O N Senkov, K J Chaput, D B Miracle, Jeanphilippe CouzinieAbstract:Open literature publications, in the period from 2010 to the end of January 2018, on Refractory high entropy Alloys (RHEAs) and Refractory complex concentrated Alloys (RCCAs) are reviewed. While RHEAs, by original definition, are Alloys consisting of five or more principal elements with the concentration of each of these elements between 5 and 35 at.%, RCCAs can contain three or more principal elements and the element concentration can be greater than 35%. The 151 reported RHEAs/RCCAs are analyzed based on their composition, processing methods, microstructures, and phases. Mechanical properties, strengthening and deformation mechanisms, oxidation, and corrosion behavior, as well as tribology, of RHEA/RCCAs are summarized. Unique properties of some of these Alloys make them promising candidates for high temperature applications beyond Ni-based superAlloys and/or conventional Refractory Alloys. Methods of development and exploration, future directions of research and development, and potential applications of RHEAs are discussed.
-
phase equilibria mechanical properties and design of quaternary Refractory high entropy Alloys
Materials & Design, 2018Co-Authors: Francisco Gil Coury, T M Butler, K J Chaput, Alec Saville, John Copley, John Foltz, Paul Mason, Kester D Clarke, M J Kaufman, A J ClarkeAbstract:Abstract Refractory high entropy Alloys (RHEAs) are candidates for replacing conventional Refractory Alloys. In this work, twelve new RHEAs were selected and produced. The phases present in the as-cast and heat-treated conditions were characterized and compared with CALPHAD simulations and empirical parameters. Here we propose a new interpretation for the two widely used δ and Ω empirical parameters. In this work, they are shown to be inaccurate when applied to a large group of RHEAs, but can be a powerful alloy design tool if applied on specific subsystems of Alloys. Experimentally, chromium-containing Alloys are shown to form Laves phases, especially when the lattice distortion (δ) is high, while aluminum-containing Alloys are shown to form the A15 phase upon heat-treatment, due to their highly negative enthalpy of mixing (ΔHmix). In addition to microstructural characterization, mechanical properties of these Alloys via hardness testing were assessed. A poor correlation was observed between the hardness and the atomic size and elastic modulus mismatch in these single-phase BCC RHEAs, suggesting that core structure of the screw dislocations is a crucial parameter in understanding the strength of these Alloys.
-
high temperature oxidation behaviors of equimolar nbtizrv and nbtizrcr Refractory complex concentrated Alloys rccas
Journal of Alloys and Compounds, 2017Co-Authors: T M Butler, K J Chaput, J R Dietrich, O N SenkovAbstract:Abstract Refractory complex concentrated Alloys (RCCAs) represent an emerging class of materials that have displayed significant potential for increased mechanical performance at extreme temperatures over conventional Refractory Alloys and Ni-base superAlloys. While limited work has been conducted in this area, several RCCAs have shown remarkable levels of oxidation resistance in comparison to the majority of uncoated commercial Refractory Alloys. However, the oxidation mechanisms in these types of Alloys have not been well understood. This study aims to develop the foundation for understanding RCCA oxidation mechanisms through the systematic evaluation of NbTiZrV and NbTiZrCr, which display vastly different oxidation behaviors. In both cases, the predominant mechanism appeared to be internal oxidation, where a mixture of simple and complex oxides was observed after prolonged oxidation times. This resulted in extended linear oxidation kinetics for the NbTiZrV alloy and linear to near-parabolic oxidation kinetics for the NbTiZrCr alloy. Under this mindset, novel design strategies for promoting increased oxidation resistance in both RCCAs and dilute Refractory Alloys based on sluggish complex oxides are proposed.
T M Butler - One of the best experts on this subject based on the ideXlab platform.
-
phase equilibria mechanical properties and design of quaternary Refractory high entropy Alloys
Materials & Design, 2018Co-Authors: Francisco Gil Coury, T M Butler, K J Chaput, Alec Saville, John Copley, John Foltz, Paul Mason, Kester D Clarke, M J Kaufman, A J ClarkeAbstract:Abstract Refractory high entropy Alloys (RHEAs) are candidates for replacing conventional Refractory Alloys. In this work, twelve new RHEAs were selected and produced. The phases present in the as-cast and heat-treated conditions were characterized and compared with CALPHAD simulations and empirical parameters. Here we propose a new interpretation for the two widely used δ and Ω empirical parameters. In this work, they are shown to be inaccurate when applied to a large group of RHEAs, but can be a powerful alloy design tool if applied on specific subsystems of Alloys. Experimentally, chromium-containing Alloys are shown to form Laves phases, especially when the lattice distortion (δ) is high, while aluminum-containing Alloys are shown to form the A15 phase upon heat-treatment, due to their highly negative enthalpy of mixing (ΔHmix). In addition to microstructural characterization, mechanical properties of these Alloys via hardness testing were assessed. A poor correlation was observed between the hardness and the atomic size and elastic modulus mismatch in these single-phase BCC RHEAs, suggesting that core structure of the screw dislocations is a crucial parameter in understanding the strength of these Alloys.
-
high temperature oxidation behaviors of equimolar nbtizrv and nbtizrcr Refractory complex concentrated Alloys rccas
Journal of Alloys and Compounds, 2017Co-Authors: T M Butler, K J Chaput, J R Dietrich, O N SenkovAbstract:Abstract Refractory complex concentrated Alloys (RCCAs) represent an emerging class of materials that have displayed significant potential for increased mechanical performance at extreme temperatures over conventional Refractory Alloys and Ni-base superAlloys. While limited work has been conducted in this area, several RCCAs have shown remarkable levels of oxidation resistance in comparison to the majority of uncoated commercial Refractory Alloys. However, the oxidation mechanisms in these types of Alloys have not been well understood. This study aims to develop the foundation for understanding RCCA oxidation mechanisms through the systematic evaluation of NbTiZrV and NbTiZrCr, which display vastly different oxidation behaviors. In both cases, the predominant mechanism appeared to be internal oxidation, where a mixture of simple and complex oxides was observed after prolonged oxidation times. This resulted in extended linear oxidation kinetics for the NbTiZrV alloy and linear to near-parabolic oxidation kinetics for the NbTiZrCr alloy. Under this mindset, novel design strategies for promoting increased oxidation resistance in both RCCAs and dilute Refractory Alloys based on sluggish complex oxides are proposed.