A Numerical Model for the Description of Massive and Lamellar Microstructure Formation in Gamma-TiAl

Alain Jacot; Amin Rostamian

doi:10.4028/www.scientific.net/MSF.539-543.1481

Paper Titles

Identification of the Chirality and Polarity of Intermetallic Compounds with the Point Groups of 23, 432, 422, and 321 by Electron Diffraction
p.1457

Vacuum Induction Melting and Investment Casting Technologies Tailored to Near-Gamma TiAl Alloys
p.1463

Processing and Mechanical Properties of RuAl-Based Alloys
p.1469

Analysis of the Solidification Microstructure of Multi- Component γ-TiAl Alloys
p.1475

A Numerical Model for the Description of Massive and Lamellar Microstructure Formation in Gamma-TiAl
p.1481

Cold-Working and Annealing of L1₀-Ordering Iron-Palladium Base Intermetallics
p.1487

Microstructures and Mechanical Properties of Directionally Solidified Intermetallic Composites
p.1495

Effects of Hf on the Microstructure and Mechanical Properties of TiAl Base Alloys
p.1501

Microstructural Control of Nb-Si Alloy with Invariant Reactions
p.1507

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A Numerical Model for the Description of Massive and Lamellar Microstructure Formation in Gamma-TiAl

Abstract:

A phenomenological modeling approach has been developed to describe the massive transformation and the formation of lamellar microstructures during cooling in gamma titanium aluminides. The modeling approach is based on a combination of nucleation and growth laws which take into account the specific mechanisms of each phase transformation. Nucleation of both massive and lamellar γ is described with classical nucleation theory, accounting for the fact that nuclei are formed predominantly at α/α grain boundaries. Growth of the massive γ grains is calculated with a mathematical expression for interface-controlled reactions. A modified Zener model is used to calculate the thickening rate of the γ lamellar precipitates. The model incorporates the effect of particle impingement and rapid coverage of the nucleation sites due to growth. The driving pressures of the phase transformations are obtained form Thermo-Calc based on actual temperature and matrix composition. The model permitted investigating the influence of alloy chemistry, cooling rate and average α grain size upon the amount of massive γ and the average thickness and spacing of the lamellae. Calculated CCT diagrams were compared with experimental data collected from the literature and showed good agreement.