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

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/>\t\t<br/>1.\tINTRODUCTION\t<br/>2\tEXPERIMENTAL ASPECTS OF CALORIMETRY\t<br/>2.1\tEXPERIMENTAL ASPECTS OF ISOTHERMAL CALORIMETRIC ANALYSIS\t<br/>2.2\tEXPERIMENTAL ASPECTS OF DIFFERENTIAL SCANNING CALORIMETRY\t<br/>2.3\tSAMPLE PREPARATION FOR CALORIMETRY OF LIGHT METAL ALLOYS.\t<br/>2.4\tBASELINE CORRECTION IN CALORIMETRY\t<br/>2.4.1\tInitial transient\t<br/>2.4.2\tBaseline variability and drift\t<br/>2.4.3\tCombined baseline variability and heat capacity effects in DSC\t<br/>3\tAPPLICATIONS OF THERMAL ANALYSIS FOR AL BASED ALLOYS.\t<br/>3.1\tIDENTIFICATION OF THERMAL EFFECTS.\t<br/>3.2\tHEAT CAPACITY DETERMINATION.\t<br/>3.3\tSOLID STATE REACTIONS\t<br/>3.3.1\tHomogenising and solution treatment studies\t<br/>3.3.2\tPrecipitation studies – Qualitative analysis\t<br/>3.3.3\tDetermination of thermal history / Fingerprinting of heat treated alloys\t<br/>3.3.4\tPrecipitate coarsening – Qualitative analysis\t<br/>3.3.5\tDefect annihilation, recovery and recrystallisation in wrought alloys\t<br/>3.3.6\tDevitrivication; nanocrystallisation<br/>3.3.7\tMulti-layers and interfacial reactions<br/>3.4\tSOLID-LIQUID AND LIQUID-SOLID REACTIONS.<br/>3.4.1\tSolidification.<br/>3.4.2\tMelting and incipient melting<br/>3.5\tCALPHAD; MIXING AND DISSOLUTION OF POWDERS AND LIQUIDS<br/>4\tMODELLING OF THERMALLY ACTIVATED REACTIONS.<br/>4.1\tINTRODUCTION; GENERAL OBJECTIVES.<br/>4.2\tSINGLE STATE VARIABLE APPROACHES (SINGLE ARRHENIUS TERM)<br/>4.3\tEQUIVALENT TIME, THE STATE VARIABLE AND THE TEMPERATURE INTEGRAL.<br/>4.3.1\tThe state variable approach and equivalent times\t<br/>4.3.2\tThe temperature integral and its approximations<br/>4.4\tACTIVATION ENERGY DETERMINATION.<br/>4.4.1\tActivation Energy analysis using isoconversion methods\t<br/>4.4.2\tAccuracies of isoconversion analysis methods<br/>4.4.3\tMeasured activation energies in Al-based alloys\t<br/>4.5\tSINGLE STAGE REACTION MODELS.\t<br/>4.5.1\tJMAK, mean field and other models <br/>4.5.2\tOther models for precipitation in Al based alloys.\t<br/>4.5.3\tDetermination of the reaction exponent, n\t<br/>4.6\tMULTI STAGE MODELS (MULTIPLE ARRHENIUS TERMS)\t<br/>5\tDETERMINATION OF VOLUME FRACTIONS OF REACTION PRODUCTS AND PHASES\t<br/>5.1\tGENERAL OBJECTIVES\t<br/>5.2\tVOLUME FRACTIONS OF PRECIPITATES MEASURED FROM SOLID-SOLID REACTIONS\t<br/>5.3\tVOLUME FRACTIONS CRYSTALLISED DURING DEVITRIVICATION\t<br/>5.4\tVOLUME FRACTIONS OF INTERMETALLIC PHASES MEASURED FROM SOLID-LIQUID REACTIONS\t<br/>6\tCONCLUDING REMARKS