1997 TMS Annual Meeting: Tuesday Abstracts

HUME-ROTHERY AWARD SYMPOSIUM FOR BRUNO PREDEL: THERMODYNAMICS OF ALLOY FORMATION: Session III: Modeling and Phase Diagram Calculation

Session Chair: F. Sommer, Max-Planck-Institut für Metallforschung, Institut für Werkstoffwissenschaft, Seestr. 75, D-70174 Stuttgart, Germany

2:00 pm INVITED

RECENT ADVANCES IN THE THERMOCHEMICAL INVESTIGATION OF SELECTED Al-Ni-R (R=RARE EARTH METALS) ALLOYS: G. Borzone, N. Parodi, R. Ferro, Dipartimento di Chimica e Chimica Industriale, Divisione di Chimica Inorganica e Metallurgia, Università di Genova, I-16146 Genova, Italy

The aluminum-based intermetallic compounds are the subject of growing interest for their combination of properties such as low density, good resistance to corrosion and heat, etc. For the Al-transition metal alloys, we may mention that the addition of rare earths to Al-rich alloys can bring about a significant modification of macro- and microstructure resulting in improvement in strength, thermal stability, etc. Several applications of selected Al-M-R (M-transition metal) alloys for their typical characteristics such as magnetic properties and hydrogen storage capability may be worthy of note. The knowledge of their thermodynamic properties may therefore be useful in gaining information on stable and metastable phases of these systems. To this end, we have begun a systematic study on the reactivity of the Al-R and Al-Ni-R alloys using calorimetric techniques, x-ray diffraction and microscopy analyses. The results so far obtained for selected Al-Ni-R alloy compositions will be illustrated and discussed.

2:30 pm

THERMODYNAMIC MODELLING AND APPLICATIONS OF THE Ti-Al-N PHASE DIAGRAM: K. Zeng and R. Schmid-Fetzer, Techn. Universitaet Clausthal, AG Elektronische Materialien, Robert-Koch-Str. 42, D-38678 Clausthal-Zellerfeld, Germany

The Ti-Al-N phase diagram has been assessed and a consistent set of thermodynamic functions has been developed. Three ternary line compounds, 1-Ti3AlN0.56, 2-Ti2AlN082, 3-Ti3Al2N2, and the interaction parameters of the ternary solution phases Ti and Ti have been modelled. The experimental phase equilibria at 1573K can be well reproduced. Inconsistencies are detected at lower temperatures, which are also related to the observed melting behavior of the ternary phases. These inconsistencies and the current approach to determine the Gibbs energies of the ternary phases are discussed in detail. Applications of the proposed thermodynamic model include the diffusion path of the Ti/AlN contact system at 1473 K, the reactions of Al+TiN powder mixtures in Al-matrix composites and Al/TiN interface reaction.

3:00 pm

APPLICATION OF EVALUATED THERMODYNAMIC DATA FOR LIGHT METAL ALLOY SYSTEMS TO CASTING AND HEAT-TREATMENT PROCESSES: P. Spencer, B. Meurer, I. Hurtado, T. Buhler, S. Fries, Lehrstuhl für Theoretische Hüttenkunde, Rheinisch-Westfälisch-Techniche Hochschule Aachen - RWTH, D-52056 Aachen

The critical thermodynamic evaluation of alloys formed from the components Al, Cu, Mg, Si, Zn to produce technologically important constitution information will be described. Isothermal sections and isopleths relevant to phase formation in commercial alloys will be presented. The use of the evaluated data to investigate phase formation sequences and enthalpy effects during solidification under equilibrium and non-equilibrium conditions will be discussed and simulations of heat-treatment processes taking into account the influence of diffusion rates on the development of phase constitution will be described.

3:30 pm BREAK

3:45 pm

UNIFIED SOLUTION MODEL FOR BINARY, TERNARY AND HIGHER ORDER METALLIC, CERAMIC SYSTEMS, AQUEOUS SOLUTIONS, POLYMER BLENDS AND FOR PHASE DIAGRAM CALCULATIONS: M. Hoch, Dept. of Materials Science and Engineering, University of Cincinnati, Cincinnati, OH 45221

The Hoch-Arsphofen model has been applied to binary, ternary and higher order metallic, ceramic systems, aqueous solutions, polymer blends and used for phase diagram calculations. The model is an expansion of the regular solution model: it assumes that in a binary system the A-B bond properties depend on the surroundings. The model was derived from ternary and quaternary systems, and no ternary or higher order interaction parameters are needed. An equation for Cp(L-s) has been developed, based on Tg, the theoretical glass transition temperature, where, below the melting point, the entropy of the liquid equals that of the solid, and the Gibbs energy difference G(L-s) is a maximum. Examples of all four types of systems are presented.

4:15 pm

INTERACTIONS BETWEEN INTERSTITIAL ATOMS AND VACANCIES IN METALS: Rex B. McLellan, Department of Mechanical Engineering and Materials Science, Rice University, PO Box 1892, Houston, TX 77251-1892

The statistical mechanics of interactions between dissolved interstitial atoms and lattice vacancies in metals is discussed. Interstitial atoms occupy sites nearest-neighbor to a monovacancy creating "decorated" vacancies. The effect of such clusters on the thermodynamic properties of the solid solution and the kinetics of the migration of both lattice atoms and interstitial solutes is considered. Specific calculations will include C - austenite and systems involving hydrogen in palladium-based binary matrixes.

4:45 pm

ENERGETICS OF ALLOY FORMATION WITHIN STATISTICAL THERMODYNAMICS AND ELECTRON THEORY: R.N. Singh, Department of Physics, Sultan Qaboos University, PO Box 36 Al-Khod, Postal Code 123, Oman

The deviations of the thermo-physical functions from the additive rule of mixing as a function of concentration, temperature and pressure is a key to the understanding of the energetics of alloy formation. Within the framework of statistical thermodynamic model, a suitable link is established between the bulk observable properties and the nature of atomic interactions in strongly and weakly correlated systems. It helps to analyze the role of enthalpic and entropic effects on alloy formation. The implications of basic interactions (i.e. electron-electron, ion-ion and electron-ion) on formation energy are also discussed from electronic theory. Pairwise interactions calculated from the first principle theory are found to have a direct correspondence to the order energy which occurs as a free parameter in various thermodynamic models.