We describe current approaches to thermodynamic modelling of liquids for the CALPHAD method, the ... more We describe current approaches to thermodynamic modelling of liquids for the CALPHAD method, the use of available experimental methods and results in this type of modelling, and considerations in the use of atomic-scale simulation methods to inform a CALPHAD approach. We begin with an overview of the formalism currently used in CALPHAD to describe the temperature dependence of the liquid Gibbs free energy and outline opportunities for improvement by reviewing the current physical understanding of the liquid. Brief descriptions of experimental methods for extracting high-temperature data on liquids and the preparation of undercooled liquid samples are presented. Properties of a well-determined substance, B 2 O 3 , including the glass transition, are then discussed in detail to emphasize specific modelling requirements for the liquid. We then examine the two-state model proposed for CALPHAD in detail and compare results with experiment and theory, where available. We further examine the contributions of atomic-scale methods to the understanding of liquids and their potential for supplementing available data. We discuss molecular dynamics (MD) and Monte Carlo methods that employ atomic interactions from classical interatomic potentials, as well as contributions from ab initio MD. We conclude with a summary of our findings. and mechanistic understanding, but these methods are not commonly applied to CALPHAD modelling of liquids. Additionally, there are known problems with existing descriptions used in CALPHAD for undercooled liquids and amorphous solid phases. Addressing these issues was the charge given to the 'Liquids' group at the 2013 Ring-berg Unary Workshop with the ultimate goal of assessing and developing better models of liquids in CALPHAD. Specifically this group was charged with determining how modelling of liquids might be improved, how limitations of the current CALPHAD models might be overcome, and with examining whether and how atomic-scale methods (such as first-principles calculations or atomistic simulation) might be used to inform or provide data on liquids for use in CAL-PHAD assessments. We will begin by reviewing the current understanding of liquids and discussing some of the limitations of the current CALPHAD approach to provide context for the remaining sections. The SGTE database [1] is the main source of elemental thermodynamic descriptions currently used in CALPHAD. This set of descriptions has two major shortcomings. One is that the extrapolation of the thermodynamic functions to temperatures below the melting point does not give meaningful values for entropy and heat capacity, and, therefore, these functions are not a good basis for the description of glassy or amorphous alloys. The other shortcoming is that these functions have artificial break points (kinks) in entropy and heat capacity functions at the melting point of the pure elements, and these break points remain as artefacts in the description of multi-component alloy liquids. When the formalism of SGTE was first presented as an 'interim' solution more than two decades ago, these shortcomings were accepted to avoid more pronounced problems during the extrapolation to metastable temperature regimes. In 1995, a workshop was organized at Ringberg to develop models for the description of the unary data that would overcome these shortcomings. One of the groups at this workshop focussed on the extrapolation of the heat capacity in liquid and amorphous phases [2]. However, only a few descriptions of the elements were developed using the recommendations from this workshop. Given that the description of undercooled liquids for unaries suggested by the SGTE database [1] is still unsatisfactory to describe the thermodynamics of liquid/amorphous phases, our goal was to treat the heat capacity, C P , for liquid and solid amorphous phases from high temperatures (defined as 2000 K at the workshop) to low temperatures, ideally 0 K. Formalisms should accommodate the thermodynamics associated with any liquid-glass transitions and be able to handle effects of high pressure. Ideally temperatures should extend up to the melting temperature of tungsten. Additionally, any CALPHAD liquid formalisms should be as physically grounded as possible. We note here that a strict definition of a unary is that it is a system consisting of one element. However, a unary is also frequently defined as a system consisting of a compound with fixed composition under conditions for which it does not decompose into other components [3]. Because of the relatively limited availability of experimental data for liquid pure elements, especially in the undercooled state, we expanded the scope to also include compound unaries in the discussions. In addition, including these compound unaries also allowed the discussion of the glass transition that is more commonly observed in these systems. First, we will discuss the current understanding of the liquid and give a detailed discussion of the issues by focussing on the case of B 2 O 3. We will then focus on the two-state model proposed in 1988 by Agren [4] for undercooled liquids and applied in 1995 by Agren et al. [2] to the description of the liquid at temperatures up to 5000 K and multi-component systems. We will then finish with some considerations in the use of theoretical data (particularly classical atomistic simulation) as part of a CALPHAD framework, followed by a summary of the paper.
In order to evaluate the impact of an oxidation resistant coating on the structural performance o... more In order to evaluate the impact of an oxidation resistant coating on the structural performance of a Mo-9Si-8B alloy tensile creep experiments were conducted at 1200 °C. After a plastic strain of 6 % the creep rates of the coated samples compared favorably with the reported values for uncoated samples. Moreover, the coating structure was maintained during creep deformation and the coating exhibited a self-healing capability.
Primary crystallization is the key reaction that controls the synthesis of nanostructured bulk vo... more Primary crystallization is the key reaction that controls the synthesis of nanostructured bulk volumes comprised of a high density (10 21-10 23 m À3) of nanocrystals (7-20 nm) within an amorphous matrix. The primary crystallization kinetics in response to the annealing and the deformation of amorphous Al alloys are assessed in specific sample types and selected thermal treatments to evaluate primary nanocrystallization reactions. All amorphous Al alloy compositions are hypereutectic so that the initial phase selection of primary Al proceeds at a reduced driving free energy compared to thermodynamically favored intermetallic phases. Differential scanning calorimetry (DSC) studies on powders and melt spun ribbon (MSR) samples based upon thermal cycling and annealing below the glass transition, T g , demonstrate a strong sensitivity of the primary crystallization onset and reaction enthalpy to thermal history and the as-quenched state. Microcalorimetry investigations and careful analysis of nanocrystal size distributions for Al 92 Sm 8 MSRs following sub-T g anneals reveal a partial nanocrystallization reaction resulting from a transient, decaying nucleation rate and a limited supply of heterogeneous nucleation sites. While crystallization is generally thought of as a thermally activated process, it can also be induced in response to external forcing such as irradiation or mechanical alloying. Intense deformation of amorphous Al 88 Y 7 Fe 5 MSR, for example, yields a distribution of Al-nanocrystallites in the amorphous matrix without thermal annealing. Moreover, the results of cold-rolling experiments with melt-spun amorphous Al 85 Ni 10 Ce 5 ribbons show that the deformation process can alter the phase selection upon annealing. These results suggest that the shear process during rolling effects a local rearrangement of atoms in the amorphous matrix. The kinetics behavior highlights the important role of the as-synthesized amorphous structure, reaction pathways and transient conditions on the evolution of nanoscale microstructures during primary crystallization.
To enhance the resistance to oxidation and prolong the lifetime, oxidation protection coatings we... more To enhance the resistance to oxidation and prolong the lifetime, oxidation protection coatings were applied on Mo-9Si-8B (in at.%) alloy substrates by Si-B co-pack cementation. Subsequently, the samples were conditioned at 1450°C for 8 h in air to develop an outer 10 μm thick aluminoborosilicate scale. A multilayered microstructure of MoSi 2 , Mo 5 Si 3 , and Mo 5 SiB 2 /MoB of about 80 μm thick was observed underneath the scale. During cyclic testing between room temperature and 1300°C the samples exhibited a very low mass change of only up to +/− 0.2 mg/cm 2 within 500 h at high temperature. During oxidation the MoSi 2 phase layer was partially consumed by silica and Mo 5 Si 3 formation. No high material regression due to MoO 3-evaporation took place during testing. However, a low mass loss during the first 100 h of testing was observed, presumably due to stress cracking caused by thermal mismatch of coating and substrate accompanied by subsequent healing. The stresses were reduced by the growth texture in the [001] direction of the Mo 5 Si 3-phase. In comparison to the uncoated substrate material, the mass change was decreased by 99.8%. This points to a significantly prolonged lifetime and shows the huge potential of coated Mo-9Si-8B alloys for application at very high temperatures and under thermal cycling loads.
In materials systems subjected to large undercooling or high supersaturation conditions, crystal ... more In materials systems subjected to large undercooling or high supersaturation conditions, crystal nucleation and growth limitations can expose alloy metastability due either to the suppression of an equilibrium phase or else by the formation of a kinetically favored metastable phase. For the case of amorphous phase formation during melt processing the kinetic control may be analyzed in terms of nucleation limitations or growth restrictions. Under nucleation control, crystallization may be bypassed in bulk volumes as the liquid is uniformly undercooled below the glass transition. Many metallic glasses require quenching for vitrification and often do not exhibit a readily resolved glass transition upon reheating. In these cases the marginal glass formation is related mainly to growth limitations. However, this same kinetic control also provides the foundation for the development of a high density (10 22 m À3) of nanometer sized (20 nm) crystals during primary crystallization. Alternatively, during interface reactions, nucleation can be suppressed at early times by large concentration gradients that can promote amorphization and can expose several forms of metastability including conditions that apply to nanostructure size scales. With other synthesis routes based upon solid state alloying resulting from deformation, the kinetic pathways to glass formation can be altered to avoid primary nanocrystallization reactions in marginal glass forming alloys. These developments present intriguing opportunities for controlling microstructural evolution especially at the nanostructure size scale.
The possibility of achieving outstanding corrosion resistance with compositionally modified iron-... more The possibility of achieving outstanding corrosion resistance with compositionally modified iron-based amorphous metals was recognized several years ago, with substantial progress made recently in the realization of this potential. Due to their unique combination of properties, these high-performance corrosion-resistant materials should find widespread use in applications such as heavy equipment manufacture, enhanced transportation infrastructure including steel reinforcement bars for concrete and steel bridges, the safe storage, transportation and disposal of spent nuclear fuel, and national defense. These materials have been shown to have excellent wear hardness with exceptional resistance to abrasion and gouges, and corrosion resistance better than that of conventional stainless steels and comparable to that of Ni-based alloys. Since their discovery, new alloy compositions have been designed and synthesized that have led to improved stability at high temperatures, well above 500°C. In addition, the boron content that is present in these new formulations provides excellent neutron absorbing characteristics that make them suitable for criticality control applications. Despite the progress made in high-performance corrosion-resistant metals (HPCRMs), there continues to be a need to master their properties, improve their quality, and quantify their performance so that their use as integral components of structural materials can be considered with a high level of confidence.
Alloys in the V-Si-B system are a new and promising class of light-weight refractory metal materi... more Alloys in the V-Si-B system are a new and promising class of light-weight refractory metal materials for high temperature applications. Presently, the main attention is focused on three-phase alloy compositions that consist of a vanadium solid solution phase and the two intermetallic phases V3Si and V5SiB2. Similar to other refractory metal alloys, a major drawback is the poor oxidation resistance. In this study, initial pack-cementation experiments were performed on commercially available pure vanadium and a three-phase alloy V-9Si-5B to achieve an oxidation protection for this new type of high temperature material. This advance in oxidation resistance now enables the attractive mechanical properties of V-Si-B alloys to be used for high temperature structural applications.
Yttrium-containing SAM1651 (Fe48.0Cr15.0Mo14.0B6.0C15.0Y2.0), has a critical cooling rate (CCR) o... more Yttrium-containing SAM1651 (Fe48.0Cr15.0Mo14.0B6.0C15.0Y2.0), has a critical cooling rate (CCR) of approximately 80 Kelvin per second, while SAM2X5 (Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4) with no yttrium has a higher critical cooling rate of approximately 600 Kelvin per second. SAM1651's low CCR enables it to be rendered as a completely amorphous material in practical materials processes. Chromium (Cr), molybdenum (Mo) and tungsten (W) provide corrosion resistance; boron (B) enables glass formation; and rare earths such as yttrium (Y) lower critical cooling rate (CCR). The passive film stability of these Fe- based amorphous metal formulations have been found to be superior to that of conventional stainless steels, and comparable to that of Ni-based alloys, based on electrochemical measurements of the passive film breakdown potential and general corrosion rates.
Volume 7: Operations, Applications, and Components, 2005
New corrosion-resistant, iron-based amorphous metals have been identified from published data or ... more New corrosion-resistant, iron-based amorphous metals have been identified from published data or developed through combinatorial synthesis, and tested to determine their relative corrosion resistance. Many of these materials can be applied as coatings with advanced thermal spray technology. Two compositions have corrosion resistance superior to wrought nickel-based Alloy C-22 (UNS # N06022) in some very aggressive environments, including concentrated calcium-chloride brines at elevated temperature. One of these compositions, SAM1651, is discussed in detail to illustrate the promise of this general class of materials.
In several Fe-based alloy systems it is possible to produce glasses with cooling rates as low as ... more In several Fe-based alloy systems it is possible to produce glasses with cooling rates as low as 100 K/s that exhibit outstanding corrosion resistance compared to typical crystalline alloys such as high-performance stainless steels and Ni-based C-22 alloy. Moreover, novel alloy compositions can be synthesized to maximize corrosion resistance (i.e. adding Cr and Mo) and to improve radiation compatibility (adding B) and still maintain glass forming ability. The applicability of Fe-based amorphous coatings in typical environments where corrosion resistance and thermal stability are critical issues has been examined in terms of amorphous phase stability and glass-forming ability through a coordinated computational analysis and experimental validation. Similarly, a novel computational thermodynamics approach has been developed to explore the compositional sensitivity of glass-forming ability and thermal stability. Also, the synthesis and characterization of alloys with increased cross-se...
ADC and Sensitive Subject Review: As an Authorized Derivative Classifier, I have reviewed this in... more ADC and Sensitive Subject Review: As an Authorized Derivative Classifier, I have reviewed this information and verify that it does not contain classified information. _____________________________________ ADC Signature This document contains no sensitive subjects: _____________________________________ Sensitive Subject Reviewer Signature Official Use Only-Exemption 4: CommerciałProprietaryprotects trade secret or confidential business information-for example, details of a unique manufacturing process, research data generated by a private corporation, or CRADA information. CRADA partners may mutually agree to withhold certain information from public disclosure for a period not to exceed five years. "Protected CRADA Information" is information that would be considered "proprietary information" if it had been produced by a non-Federal entity.
The multi-institutional High Performance Corrosion Resistant Materials (HPCRM) Team is cosponsore... more The multi-institutional High Performance Corrosion Resistant Materials (HPCRM) Team is cosponsored by the Defense Advanced Projects Agency (DARPA) Defense Science Office (DSO) and the Department of Energy (DOE) Office of Civilian Radioactive Waste Management (OCRWM), and has developed new corrosion-resistant, iron-based amorphous metals that can be applied as coatings with advanced thermal spray technology. Two compositions have corrosion resistance superior to wrought nickel-based Alloy C-22 (UNS # N06022) in very aggressive environments, including concentrated calcium-chloride brines at elevated temperature. Corrosion costs the Department of Defense billions of dollars every year, with an immense quantity of material in various structures undergoing corrosion. For example, in addition to fluid and seawater piping, ballast tanks, and propulsions systems, approximately 345 million square feet of structure aboard naval ships and crafts require costly corrosion control measures. The use of advanced corrosion-resistant materials to prevent the continuous degradation of this massive surface area would be extremely beneficial. The Fe-based corrosion-resistant, amorphous-metal coatings under development may prove of importance for applications on ships. Such coatings could be used as an "integral drip shield" on spent fuel containers, as well as protective coatings that could be applied over welds, thereby preventing exposure to environments that might cause stress corrosion cracking. In the future, such new highperformance iron-based materials could be substituted for more-expensive nickel-based alloys, thereby enabling a reduction in the $58-billion life cycle cost for the long-term storage of the Nation's spent nuclear fuel by tens of percent.
Electrochemical Studies of Passive Film Stability on Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4 Amo... more Electrochemical Studies of Passive Film Stability on Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4 Amorphous Metal in Seawater at 90oCElectrochemical Studies of Passive Film Stability on Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4 Amorphous Metal in Seawater at 90C61616;C
Aluminum-rich metallic glasses containing transition metals and rare earth elements have been fou... more Aluminum-rich metallic glasses containing transition metals and rare earth elements have been found to yield finely mixed microstructures of Al nanocrystals embedded in an amorphous matrix and exhibit enhanced fracture strength with several percent strain. Upon primary crystallization of melt spun ribbons, this novel microstructure comprised of a high particle density (>1020 m−3) of Al nanocrystals (20 nm) in an amorphous matrix develops and offers exceptional strength (1500 MPa) and high temperature stability (533 K). Numerical modeling based upon the size distribution of the Al nanocrystals after isothermal annealing is applied to study the nucleation kinetics in the metallic glasses. In addition to the kinetic study of primary nanocrystallization, the glass transition temperature (Tg) has been assessed in Al–7at.% Y–5at.% Fe and Al–8at.% Sm alloys. In usual calorimetric measurements, the thermal response of the primary crystallization often obscures the observation of the signal corresponding to the glass transition. As a result, Tg is often assumed to be near the onset of the primary crystallization reaction (TxAl). However, it has been demonstrated by modulated-temperature calorimetry that this assumption does not apply strictly to the metallic glasses under study. The thermal stabilization of the microstructure by the occurrence of diffusion field impingement allows for the observation of the glass transition of the remaining amorphous phase in the matrix by modulated differntial scanning calorimetry (DSC). The reliable assessment of the glass transition temperature provides not only a fundamental basis for the kinetics analysis, but also an important parameter in designing suitable annealing treatments that allow for the development of desired microstructures to yield optimized properties.
In systems with larger undercoolings, crystal nucleation and growth limitations can expose alloy ... more In systems with larger undercoolings, crystal nucleation and growth limitations can expose alloy metastability due either to the suppression of an equilibrium phase or else by the formation of a kinetically favored metastable phase. Under nucleation control, crystallization may be bypassed in bulk volumes as the liquid is uniformly undercooled below the glass transition. Alternatively, during interface reactions, nucleation can
New corrosion-resistant, iron-based amorphous metals have been identified from published data or ... more New corrosion-resistant, iron-based amorphous metals have been identified from published data or developed through combinatorial synthesis, and tested to determine their relative corrosion resistance. Many of these materials can be applied as coatings with advanced thermal spray technology. Two compositions have corrosion resistance superior to wrought nickel-based Alloy C-22 (UNS # N06022) in some very aggressive environments, including concentrated calciumchloride brines at elevated temperature.
We describe current approaches to thermodynamic modelling of liquids for the CALPHAD method, the ... more We describe current approaches to thermodynamic modelling of liquids for the CALPHAD method, the use of available experimental methods and results in this type of modelling, and considerations in the use of atomic-scale simulation methods to inform a CALPHAD approach. We begin with an overview of the formalism currently used in CALPHAD to describe the temperature dependence of the liquid Gibbs free energy and outline opportunities for improvement by reviewing the current physical understanding of the liquid. Brief descriptions of experimental methods for extracting high-temperature data on liquids and the preparation of undercooled liquid samples are presented. Properties of a well-determined substance, B 2 O 3 , including the glass transition, are then discussed in detail to emphasize specific modelling requirements for the liquid. We then examine the two-state model proposed for CALPHAD in detail and compare results with experiment and theory, where available. We further examine the contributions of atomic-scale methods to the understanding of liquids and their potential for supplementing available data. We discuss molecular dynamics (MD) and Monte Carlo methods that employ atomic interactions from classical interatomic potentials, as well as contributions from ab initio MD. We conclude with a summary of our findings. and mechanistic understanding, but these methods are not commonly applied to CALPHAD modelling of liquids. Additionally, there are known problems with existing descriptions used in CALPHAD for undercooled liquids and amorphous solid phases. Addressing these issues was the charge given to the 'Liquids' group at the 2013 Ring-berg Unary Workshop with the ultimate goal of assessing and developing better models of liquids in CALPHAD. Specifically this group was charged with determining how modelling of liquids might be improved, how limitations of the current CALPHAD models might be overcome, and with examining whether and how atomic-scale methods (such as first-principles calculations or atomistic simulation) might be used to inform or provide data on liquids for use in CAL-PHAD assessments. We will begin by reviewing the current understanding of liquids and discussing some of the limitations of the current CALPHAD approach to provide context for the remaining sections. The SGTE database [1] is the main source of elemental thermodynamic descriptions currently used in CALPHAD. This set of descriptions has two major shortcomings. One is that the extrapolation of the thermodynamic functions to temperatures below the melting point does not give meaningful values for entropy and heat capacity, and, therefore, these functions are not a good basis for the description of glassy or amorphous alloys. The other shortcoming is that these functions have artificial break points (kinks) in entropy and heat capacity functions at the melting point of the pure elements, and these break points remain as artefacts in the description of multi-component alloy liquids. When the formalism of SGTE was first presented as an 'interim' solution more than two decades ago, these shortcomings were accepted to avoid more pronounced problems during the extrapolation to metastable temperature regimes. In 1995, a workshop was organized at Ringberg to develop models for the description of the unary data that would overcome these shortcomings. One of the groups at this workshop focussed on the extrapolation of the heat capacity in liquid and amorphous phases [2]. However, only a few descriptions of the elements were developed using the recommendations from this workshop. Given that the description of undercooled liquids for unaries suggested by the SGTE database [1] is still unsatisfactory to describe the thermodynamics of liquid/amorphous phases, our goal was to treat the heat capacity, C P , for liquid and solid amorphous phases from high temperatures (defined as 2000 K at the workshop) to low temperatures, ideally 0 K. Formalisms should accommodate the thermodynamics associated with any liquid-glass transitions and be able to handle effects of high pressure. Ideally temperatures should extend up to the melting temperature of tungsten. Additionally, any CALPHAD liquid formalisms should be as physically grounded as possible. We note here that a strict definition of a unary is that it is a system consisting of one element. However, a unary is also frequently defined as a system consisting of a compound with fixed composition under conditions for which it does not decompose into other components [3]. Because of the relatively limited availability of experimental data for liquid pure elements, especially in the undercooled state, we expanded the scope to also include compound unaries in the discussions. In addition, including these compound unaries also allowed the discussion of the glass transition that is more commonly observed in these systems. First, we will discuss the current understanding of the liquid and give a detailed discussion of the issues by focussing on the case of B 2 O 3. We will then focus on the two-state model proposed in 1988 by Agren [4] for undercooled liquids and applied in 1995 by Agren et al. [2] to the description of the liquid at temperatures up to 5000 K and multi-component systems. We will then finish with some considerations in the use of theoretical data (particularly classical atomistic simulation) as part of a CALPHAD framework, followed by a summary of the paper.
In order to evaluate the impact of an oxidation resistant coating on the structural performance o... more In order to evaluate the impact of an oxidation resistant coating on the structural performance of a Mo-9Si-8B alloy tensile creep experiments were conducted at 1200 °C. After a plastic strain of 6 % the creep rates of the coated samples compared favorably with the reported values for uncoated samples. Moreover, the coating structure was maintained during creep deformation and the coating exhibited a self-healing capability.
Primary crystallization is the key reaction that controls the synthesis of nanostructured bulk vo... more Primary crystallization is the key reaction that controls the synthesis of nanostructured bulk volumes comprised of a high density (10 21-10 23 m À3) of nanocrystals (7-20 nm) within an amorphous matrix. The primary crystallization kinetics in response to the annealing and the deformation of amorphous Al alloys are assessed in specific sample types and selected thermal treatments to evaluate primary nanocrystallization reactions. All amorphous Al alloy compositions are hypereutectic so that the initial phase selection of primary Al proceeds at a reduced driving free energy compared to thermodynamically favored intermetallic phases. Differential scanning calorimetry (DSC) studies on powders and melt spun ribbon (MSR) samples based upon thermal cycling and annealing below the glass transition, T g , demonstrate a strong sensitivity of the primary crystallization onset and reaction enthalpy to thermal history and the as-quenched state. Microcalorimetry investigations and careful analysis of nanocrystal size distributions for Al 92 Sm 8 MSRs following sub-T g anneals reveal a partial nanocrystallization reaction resulting from a transient, decaying nucleation rate and a limited supply of heterogeneous nucleation sites. While crystallization is generally thought of as a thermally activated process, it can also be induced in response to external forcing such as irradiation or mechanical alloying. Intense deformation of amorphous Al 88 Y 7 Fe 5 MSR, for example, yields a distribution of Al-nanocrystallites in the amorphous matrix without thermal annealing. Moreover, the results of cold-rolling experiments with melt-spun amorphous Al 85 Ni 10 Ce 5 ribbons show that the deformation process can alter the phase selection upon annealing. These results suggest that the shear process during rolling effects a local rearrangement of atoms in the amorphous matrix. The kinetics behavior highlights the important role of the as-synthesized amorphous structure, reaction pathways and transient conditions on the evolution of nanoscale microstructures during primary crystallization.
To enhance the resistance to oxidation and prolong the lifetime, oxidation protection coatings we... more To enhance the resistance to oxidation and prolong the lifetime, oxidation protection coatings were applied on Mo-9Si-8B (in at.%) alloy substrates by Si-B co-pack cementation. Subsequently, the samples were conditioned at 1450°C for 8 h in air to develop an outer 10 μm thick aluminoborosilicate scale. A multilayered microstructure of MoSi 2 , Mo 5 Si 3 , and Mo 5 SiB 2 /MoB of about 80 μm thick was observed underneath the scale. During cyclic testing between room temperature and 1300°C the samples exhibited a very low mass change of only up to +/− 0.2 mg/cm 2 within 500 h at high temperature. During oxidation the MoSi 2 phase layer was partially consumed by silica and Mo 5 Si 3 formation. No high material regression due to MoO 3-evaporation took place during testing. However, a low mass loss during the first 100 h of testing was observed, presumably due to stress cracking caused by thermal mismatch of coating and substrate accompanied by subsequent healing. The stresses were reduced by the growth texture in the [001] direction of the Mo 5 Si 3-phase. In comparison to the uncoated substrate material, the mass change was decreased by 99.8%. This points to a significantly prolonged lifetime and shows the huge potential of coated Mo-9Si-8B alloys for application at very high temperatures and under thermal cycling loads.
In materials systems subjected to large undercooling or high supersaturation conditions, crystal ... more In materials systems subjected to large undercooling or high supersaturation conditions, crystal nucleation and growth limitations can expose alloy metastability due either to the suppression of an equilibrium phase or else by the formation of a kinetically favored metastable phase. For the case of amorphous phase formation during melt processing the kinetic control may be analyzed in terms of nucleation limitations or growth restrictions. Under nucleation control, crystallization may be bypassed in bulk volumes as the liquid is uniformly undercooled below the glass transition. Many metallic glasses require quenching for vitrification and often do not exhibit a readily resolved glass transition upon reheating. In these cases the marginal glass formation is related mainly to growth limitations. However, this same kinetic control also provides the foundation for the development of a high density (10 22 m À3) of nanometer sized (20 nm) crystals during primary crystallization. Alternatively, during interface reactions, nucleation can be suppressed at early times by large concentration gradients that can promote amorphization and can expose several forms of metastability including conditions that apply to nanostructure size scales. With other synthesis routes based upon solid state alloying resulting from deformation, the kinetic pathways to glass formation can be altered to avoid primary nanocrystallization reactions in marginal glass forming alloys. These developments present intriguing opportunities for controlling microstructural evolution especially at the nanostructure size scale.
The possibility of achieving outstanding corrosion resistance with compositionally modified iron-... more The possibility of achieving outstanding corrosion resistance with compositionally modified iron-based amorphous metals was recognized several years ago, with substantial progress made recently in the realization of this potential. Due to their unique combination of properties, these high-performance corrosion-resistant materials should find widespread use in applications such as heavy equipment manufacture, enhanced transportation infrastructure including steel reinforcement bars for concrete and steel bridges, the safe storage, transportation and disposal of spent nuclear fuel, and national defense. These materials have been shown to have excellent wear hardness with exceptional resistance to abrasion and gouges, and corrosion resistance better than that of conventional stainless steels and comparable to that of Ni-based alloys. Since their discovery, new alloy compositions have been designed and synthesized that have led to improved stability at high temperatures, well above 500°C. In addition, the boron content that is present in these new formulations provides excellent neutron absorbing characteristics that make them suitable for criticality control applications. Despite the progress made in high-performance corrosion-resistant metals (HPCRMs), there continues to be a need to master their properties, improve their quality, and quantify their performance so that their use as integral components of structural materials can be considered with a high level of confidence.
Alloys in the V-Si-B system are a new and promising class of light-weight refractory metal materi... more Alloys in the V-Si-B system are a new and promising class of light-weight refractory metal materials for high temperature applications. Presently, the main attention is focused on three-phase alloy compositions that consist of a vanadium solid solution phase and the two intermetallic phases V3Si and V5SiB2. Similar to other refractory metal alloys, a major drawback is the poor oxidation resistance. In this study, initial pack-cementation experiments were performed on commercially available pure vanadium and a three-phase alloy V-9Si-5B to achieve an oxidation protection for this new type of high temperature material. This advance in oxidation resistance now enables the attractive mechanical properties of V-Si-B alloys to be used for high temperature structural applications.
Yttrium-containing SAM1651 (Fe48.0Cr15.0Mo14.0B6.0C15.0Y2.0), has a critical cooling rate (CCR) o... more Yttrium-containing SAM1651 (Fe48.0Cr15.0Mo14.0B6.0C15.0Y2.0), has a critical cooling rate (CCR) of approximately 80 Kelvin per second, while SAM2X5 (Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4) with no yttrium has a higher critical cooling rate of approximately 600 Kelvin per second. SAM1651's low CCR enables it to be rendered as a completely amorphous material in practical materials processes. Chromium (Cr), molybdenum (Mo) and tungsten (W) provide corrosion resistance; boron (B) enables glass formation; and rare earths such as yttrium (Y) lower critical cooling rate (CCR). The passive film stability of these Fe- based amorphous metal formulations have been found to be superior to that of conventional stainless steels, and comparable to that of Ni-based alloys, based on electrochemical measurements of the passive film breakdown potential and general corrosion rates.
Volume 7: Operations, Applications, and Components, 2005
New corrosion-resistant, iron-based amorphous metals have been identified from published data or ... more New corrosion-resistant, iron-based amorphous metals have been identified from published data or developed through combinatorial synthesis, and tested to determine their relative corrosion resistance. Many of these materials can be applied as coatings with advanced thermal spray technology. Two compositions have corrosion resistance superior to wrought nickel-based Alloy C-22 (UNS # N06022) in some very aggressive environments, including concentrated calcium-chloride brines at elevated temperature. One of these compositions, SAM1651, is discussed in detail to illustrate the promise of this general class of materials.
In several Fe-based alloy systems it is possible to produce glasses with cooling rates as low as ... more In several Fe-based alloy systems it is possible to produce glasses with cooling rates as low as 100 K/s that exhibit outstanding corrosion resistance compared to typical crystalline alloys such as high-performance stainless steels and Ni-based C-22 alloy. Moreover, novel alloy compositions can be synthesized to maximize corrosion resistance (i.e. adding Cr and Mo) and to improve radiation compatibility (adding B) and still maintain glass forming ability. The applicability of Fe-based amorphous coatings in typical environments where corrosion resistance and thermal stability are critical issues has been examined in terms of amorphous phase stability and glass-forming ability through a coordinated computational analysis and experimental validation. Similarly, a novel computational thermodynamics approach has been developed to explore the compositional sensitivity of glass-forming ability and thermal stability. Also, the synthesis and characterization of alloys with increased cross-se...
ADC and Sensitive Subject Review: As an Authorized Derivative Classifier, I have reviewed this in... more ADC and Sensitive Subject Review: As an Authorized Derivative Classifier, I have reviewed this information and verify that it does not contain classified information. _____________________________________ ADC Signature This document contains no sensitive subjects: _____________________________________ Sensitive Subject Reviewer Signature Official Use Only-Exemption 4: CommerciałProprietaryprotects trade secret or confidential business information-for example, details of a unique manufacturing process, research data generated by a private corporation, or CRADA information. CRADA partners may mutually agree to withhold certain information from public disclosure for a period not to exceed five years. "Protected CRADA Information" is information that would be considered "proprietary information" if it had been produced by a non-Federal entity.
The multi-institutional High Performance Corrosion Resistant Materials (HPCRM) Team is cosponsore... more The multi-institutional High Performance Corrosion Resistant Materials (HPCRM) Team is cosponsored by the Defense Advanced Projects Agency (DARPA) Defense Science Office (DSO) and the Department of Energy (DOE) Office of Civilian Radioactive Waste Management (OCRWM), and has developed new corrosion-resistant, iron-based amorphous metals that can be applied as coatings with advanced thermal spray technology. Two compositions have corrosion resistance superior to wrought nickel-based Alloy C-22 (UNS # N06022) in very aggressive environments, including concentrated calcium-chloride brines at elevated temperature. Corrosion costs the Department of Defense billions of dollars every year, with an immense quantity of material in various structures undergoing corrosion. For example, in addition to fluid and seawater piping, ballast tanks, and propulsions systems, approximately 345 million square feet of structure aboard naval ships and crafts require costly corrosion control measures. The use of advanced corrosion-resistant materials to prevent the continuous degradation of this massive surface area would be extremely beneficial. The Fe-based corrosion-resistant, amorphous-metal coatings under development may prove of importance for applications on ships. Such coatings could be used as an "integral drip shield" on spent fuel containers, as well as protective coatings that could be applied over welds, thereby preventing exposure to environments that might cause stress corrosion cracking. In the future, such new highperformance iron-based materials could be substituted for more-expensive nickel-based alloys, thereby enabling a reduction in the $58-billion life cycle cost for the long-term storage of the Nation's spent nuclear fuel by tens of percent.
Electrochemical Studies of Passive Film Stability on Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4 Amo... more Electrochemical Studies of Passive Film Stability on Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4 Amorphous Metal in Seawater at 90oCElectrochemical Studies of Passive Film Stability on Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4 Amorphous Metal in Seawater at 90C61616;C
Aluminum-rich metallic glasses containing transition metals and rare earth elements have been fou... more Aluminum-rich metallic glasses containing transition metals and rare earth elements have been found to yield finely mixed microstructures of Al nanocrystals embedded in an amorphous matrix and exhibit enhanced fracture strength with several percent strain. Upon primary crystallization of melt spun ribbons, this novel microstructure comprised of a high particle density (>1020 m−3) of Al nanocrystals (20 nm) in an amorphous matrix develops and offers exceptional strength (1500 MPa) and high temperature stability (533 K). Numerical modeling based upon the size distribution of the Al nanocrystals after isothermal annealing is applied to study the nucleation kinetics in the metallic glasses. In addition to the kinetic study of primary nanocrystallization, the glass transition temperature (Tg) has been assessed in Al–7at.% Y–5at.% Fe and Al–8at.% Sm alloys. In usual calorimetric measurements, the thermal response of the primary crystallization often obscures the observation of the signal corresponding to the glass transition. As a result, Tg is often assumed to be near the onset of the primary crystallization reaction (TxAl). However, it has been demonstrated by modulated-temperature calorimetry that this assumption does not apply strictly to the metallic glasses under study. The thermal stabilization of the microstructure by the occurrence of diffusion field impingement allows for the observation of the glass transition of the remaining amorphous phase in the matrix by modulated differntial scanning calorimetry (DSC). The reliable assessment of the glass transition temperature provides not only a fundamental basis for the kinetics analysis, but also an important parameter in designing suitable annealing treatments that allow for the development of desired microstructures to yield optimized properties.
In systems with larger undercoolings, crystal nucleation and growth limitations can expose alloy ... more In systems with larger undercoolings, crystal nucleation and growth limitations can expose alloy metastability due either to the suppression of an equilibrium phase or else by the formation of a kinetically favored metastable phase. Under nucleation control, crystallization may be bypassed in bulk volumes as the liquid is uniformly undercooled below the glass transition. Alternatively, during interface reactions, nucleation can
New corrosion-resistant, iron-based amorphous metals have been identified from published data or ... more New corrosion-resistant, iron-based amorphous metals have been identified from published data or developed through combinatorial synthesis, and tested to determine their relative corrosion resistance. Many of these materials can be applied as coatings with advanced thermal spray technology. Two compositions have corrosion resistance superior to wrought nickel-based Alloy C-22 (UNS # N06022) in some very aggressive environments, including concentrated calciumchloride brines at elevated temperature.
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