Thermodynamics of liquid and undercooled liquidAl–Cr–Ni alloys

Differential scanning calorimetry (DSC) and isothermal calorimetry have been applied extensively to the analysis of light metals, especially Al based alloys. Isothermal calorimetry and differential scanning calorimetry are used for analysis of solid state reactions, such as precipitation, homogenisation, devitrivication and recrystallisation; and solid-liquid reactions, such as incipient melting and solidification, are studied by differential scanning calorimetry. In producing repeatable calorimetry data on Al alloys, sample preparation, reproducibility and baseline drift need to be considered in detail. Calorimetry can be used effectively to study the different solid state reactions and solid-liquid reactions that occur during the main processing steps of Al based alloys (solidification, homogenisation, precipitation). Also, devitrivication of amorphous and ultrafine grained Al based powders and flakes can be studied effectively. Quantitative analysis of the kinetics of reactions is assessed through reviewing the interrelation between activation energy analysis methods, equivalent time approaches, impingement parameter approaches, mean field models for precipitation, the Johnson-Mehl-Avrami-Kolmogorov model, as well as novel models which have not yet found application in calorimetry. Differential scanning calorimetry has occasionally been used in attempts to measure the volume fractions of phases present in Al based alloys, and attempts at determining volume fractions of intermetallic phases in commercial alloys and amounts of devitrified phase in glasses are reviewed. The requirements for the validity of these quantitative applications are also reviewed.Keywords: Differential scanning calorimetry, Precipitation, Aluminium, Modelling, Transformation IMR/419 IntroductionCalorimetry is an analysis technique that is part of a group of techniques collectively known as thermal analysis methods. In its broadest sense, thermal analysis refers to the measurement of changes in properties of substances under a controlled temperature program. Thermal analysis techniques can be classified according to the type of temperature program that the sample is subjected to and the measured (output) signal. The most commonly used temperature programs are either isothermal hold or heating (scanning) at constant rate, while more recently, temperature modulated scanning and reaction controlled heating have also found application. The signals measured in thermal analysis can include heat flows, temperature changes, mass, evolved gasses, length changes, elastic modulus, and many other properties that characterise properties or reactions of interest. Calorimetry refers to thermal analysis methods that measure the heat evolution from a sample under a controlled temperature program. The two most often applied calorimetry techniques are isothermal calorimetry and differential scanning calorimetry (DSC), which, as the name suggests, is by definition non-isothermal (i.e. a temperature scan). Apart from the more common applications to polymers,...

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“…[110][111][112] Further thermodynamic data can be obtained by measuring the enthalpies of dissolution of elements in liquid Al. …”

Section: 100mentioning

confidence: 99%

“…109 Enthalpies of mixing of liquid phases are measured by high temperature calorimetry. [110][111][112] Further thermodynamic data can be obtained by measuring the enthalpies of dissolution of elements in liquid Al. …”

Section: Melting and Incipient Meltingmentioning

confidence: 99%

Analysis of aluminium based alloys by calorimetry: quantitative analysis of reactions and reaction kinetics

Starink¹

2004

International Materials Reviews

287

108

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“…The value of the surface tension calculated by assuming ideal mixing and taking the surface tension values of the alloy components at their melting points as given by Keene [14] is obtained as r(T l ) = 1.679 ± 0.025 Nm -1 which is lower than the value of r(T l ) = 1.79 ± 0.05 Nm -1 from this experiment. This comparison, however, neglects the large differences in the melting points of the individual alloy components, the influence of dissolved oxygen, the non-ideality of the alloy compositon [15] or the formation of compounds, [16] and the possibility of surface segregation. [17] Recently, two experiments by the sessile drop method by Hayashi [18] et al and by Ricci [19] et al have provided values of r(T l ) = 1.97 Nm -1 and r(T l ) = 1.…”

Section: Surface Tensionmentioning

confidence: 99%

Surface Tension and Viscosity of the Ni‐based Superalloy CMSX‐4 Measured by the Oscillating Drop Method in Parabolic Flight Experiments

2007

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The surface tension and the viscosity are two important thermophysical properties in the numerical modelling of industrial casting and welding such as form filling, convective heat transfer, and the prediction of defects such as microporosity. [1,2] The most widely used techniques for surface tension measurements are the sessile and the pendant drop technique. For high-temperature reactive alloys the former may be affected by chemical reactions of the liquid alloy with the sample container which may change the surface tension. The pendant drop [3] method can provide accurate values of the surface tension at the liquidus temperature. Its application to alloys with an extended melting range is, however, complicated by the presence of concentration gradients at the position of drop formation. Similar arguments may apply to viscosity measurements by the oscillating or rotating cup method making the application of containerless methods for surface tension and viscosity measurements an interesting alternative for high-temperature reactive alloys. One advantage of containerless processing conditions is the absence of container reactions which, depending on alloy composition and temperature, can have a pronounced effect on the surface tension and its temperature coefficient. Measurements of the surface tension can be performed by the oscillating drop method on electromagnetically levitated specimen. Electromagnetic levitation under normal gravity, 1 g, conditions requires a strong magnetic fields which deform the specimen and induce turbulent fluid flow. A correction algorithm has been developed to account for the effects of the magnetic pressure and shape deformations on the surface oscillation spectrum [4] which has been validated in a series of microgravity experiments. [5] The effect of the turbulent fluid flow on the damping time constant of the surface oscillations can, however, not be accounted for in a quantitative way and, thus, requires a much reduced levitation force as afforded under reduced gravity conditions.Measurements of the surface tension and of the viscosity by the oscillating drop method on electromagnetically levitated specimen have been performed in long-duration experiments on the MSL-1 Spacelab missions. [6,7] Under ideal, nearly force free conditions as provided in reduced gravity, the oscillation spectrum is non-shifted and characterized by a single well defined oscillation peak and the absence of turbulent fluid flow. Parabolic flights with about twenty seconds of reduced gravity offer an interesting possibility for the measurement of the surface tension and viscosity of high-temperature reactive alloys by the oscillating drop method with an electromagnetic levitation device. This approach was investigated with the Ni-based superalloy CMSX-4. The experiments were performed within the framework of an ongoing European project for the measurement of the thermophysical properties of industrial alloys named ThermoLab. Experimental Sample PreparationCMSX-4 specimen were provided by an industrial par...

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“…Cr-and Ni-based superalloys have excellent hightemperature strength, good corrosion resistance, low thermal expansion and are suitable for high performance aerospace, automobile and power plant applications. The Al-Cr and Cr-Ni systems have been studied extensively as constituents of complex superalloys based on the Al-Cr-Ni system [5]. Indeed, the AlNi-Cr-Ni subsection is a model system for superalloys [6].…”

Section: Introductionmentioning

confidence: 99%

Bulk and surface properties of liquid Al–Cr and Cr–Ni alloys

Novaković

2011

J. Phys.: Condens. Matter

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The energetics of mixing and structural arrangement in liquid Al-Cr and Cr-Ni alloys has been analysed through the study of surface properties (surface tension and surface segregation), dynamic properties (chemical diffusion) and microscopic functions (concentration fluctuations in the long-wavelength limit and chemical short-range order parameter) in the framework of statistical mechanical theory in conjunction with quasi-lattice theory. The Al-Cr phase diagram exhibits the existence of different intermetallic compounds in the solid state, while that of Cr-Ni is a simple eutectic-type phase diagram at high temperatures and includes the low-temperature peritectoid reaction in the range near a CrNi(2) composition. Accordingly, the mixing behaviour in Al-Cr and Cr-Ni alloy melts was studied using the complex formation model in the weak interaction approximation and by postulating Al(8)Cr(5) and CrNi(2) chemical complexes, respectively, as energetically favoured.

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Thermodynamics of liquid and undercooled liquidAl–Cr–Ni alloys

Cited by 7 publications

References 0 publications

Analysis of aluminium based alloys by calorimetry: quantitative analysis of reactions and reaction kinetics

Analysis of aluminium based alloys by calorimetry: quantitative analysis of reactions and reaction kinetics

Surface Tension and Viscosity of the Ni‐based Superalloy CMSX‐4 Measured by the Oscillating Drop Method in Parabolic Flight Experiments

Bulk and surface properties of liquid Al–Cr and Cr–Ni alloys

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