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The analysis of Al-based alloys by calorimetry: quantitative analysis of reactions and reaction kinetics

By M.J. Starink

Abstract

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. <br/><br/>Contents<br/> <br/>1. INTRODUCTION <br/>2 EXPERIMENTAL ASPECTS OF CALORIMETRY <br/>2.1 EXPERIMENTAL ASPECTS OF ISOTHERMAL CALORIMETRIC ANALYSIS <br/>2.2 EXPERIMENTAL ASPECTS OF DIFFERENTIAL SCANNING CALORIMETRY <br/>2.3 SAMPLE PREPARATION FOR CALORIMETRY OF LIGHT METAL ALLOYS. <br/>2.4 BASELINE CORRECTION IN CALORIMETRY <br/>2.4.1 Initial transient <br/>2.4.2 Baseline variability and drift <br/>2.4.3 Combined baseline variability and heat capacity effects in DSC <br/>3 APPLICATIONS OF THERMAL ANALYSIS FOR AL BASED ALLOYS. <br/>3.1 IDENTIFICATION OF THERMAL EFFECTS. <br/>3.2 HEAT CAPACITY DETERMINATION. <br/>3.3 SOLID STATE REACTIONS <br/>3.3.1 Homogenising and solution treatment studies <br/>3.3.2 Precipitation studies – Qualitative analysis <br/>3.3.3 Determination of thermal history / Fingerprinting of heat treated alloys <br/>3.3.4 Precipitate coarsening – Qualitative analysis <br/>3.3.5 Defect annihilation, recovery and recrystallisation in wrought alloys <br/>3.3.6 Devitrivication; nanocrystallisation<br/>3.3.7 Multi-layers and interfacial reactions<br/>3.4 SOLID-LIQUID AND LIQUID-SOLID REACTIONS.<br/>3.4.1 Solidification.<br/>3.4.2 Melting and incipient melting<br/>3.5 CALPHAD; MIXING AND DISSOLUTION OF POWDERS AND LIQUIDS<br/>4 MODELLING OF THERMALLY ACTIVATED REACTIONS.<br/>4.1 INTRODUCTION; GENERAL OBJECTIVES.<br/>4.2 SINGLE STATE VARIABLE APPROACHES (SINGLE ARRHENIUS TERM)<br/>4.3 EQUIVALENT TIME, THE STATE VARIABLE AND THE TEMPERATURE INTEGRAL.<br/>4.3.1 The state variable approach and equivalent times <br/>4.3.2 The temperature integral and its approximations<br/>4.4 ACTIVATION ENERGY DETERMINATION.<br/>4.4.1 Activation Energy analysis using isoconversion methods <br/>4.4.2 Accuracies of isoconversion analysis methods<br/>4.4.3 Measured activation energies in Al-based alloys <br/>4.5 SINGLE STAGE REACTION MODELS. <br/>4.5.1 JMAK, mean field and other models <br/>4.5.2 Other models for precipitation in Al based alloys. <br/>4.5.3 Determination of the reaction exponent, n <br/>4.6 MULTI STAGE MODELS (MULTIPLE ARRHENIUS TERMS) <br/>5 DETERMINATION OF VOLUME FRACTIONS OF REACTION PRODUCTS AND PHASES <br/>5.1 GENERAL OBJECTIVES <br/>5.2 VOLUME FRACTIONS OF PRECIPITATES MEASURED FROM SOLID-SOLID REACTIONS <br/>5.3 VOLUME FRACTIONS CRYSTALLISED DURING DEVITRIVICATION <br/>5.4 VOLUME FRACTIONS OF INTERMETALLIC PHASES MEASURED FROM SOLID-LIQUID REACTIONS <br/>6 CONCLUDING REMARK

Topics: TN
Year: 2004
OAI identifier: oai:eprints.soton.ac.uk:22507
Provided by: e-Prints Soton

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