Nitrides and Oxynitrides III

Vol. 554

Vol. 554

Diffusion in Solids and Liquids II, DSL-2006 II

Vol. 553

Vol. 553

Superplasticity in Advanced Materials - ICSAM 2006

Vols. 551-552

Vols. 551-552

Fundamentals of Deformation and Annealing

Vol. 550

Vol. 550

Progress in Light Metals, Aerospace Materials and Superconductors

Vols. 546-549

Vols. 546-549

Eco-Materials Processing and Design VIII

Vols. 544-545

Vols. 544-545

THERMEC 2006

Vols. 539-543

Vols. 539-543

Materials Science, Testing and Informatics III

Vols. 537-538

Vols. 537-538

Progress in Powder Metallurgy

Vols. 534-536

Vols. 534-536

Advances in Materials Manufacturing Science and Technology II

Vols. 532-533

Vols. 532-533

Advanced Powder Technology V

Vols. 530-531

Vols. 530-531

Silicon Carbide and Related Materials 2005

Vols. 527-529

Vols. 527-529

Advances in Materials Processing Technologies, 2006

Vol. 526

Vol. 526

# THERMEC 2006

Volumes 539-543

Paper Title Page

Abstract: A tracking procedure for the high-resolution X-ray computed tomography (CT) has been
developed in order to measure 3-D local strain within a deforming material in high-density. A
dispersion-strengthened copper alloy model sample with alumina particles, which contains micropores,
was visualized by the synchrotron radiation CT. The pores observed in reconstructed CT
volumes were used as tracking markers. The developed tracking method using a set of matching
parameters, which classifies matched, pended and rejected markers, exhibited high ratio of success
tracking. Furthermore, the ratio was improved by applying the spring model method, which is one
of the particle image velocity (PIV) methods utilized in the field of the fluid mechanics, to the
pended markers. The method based on the image analysis of CT imaging volumes provides us 3-D
high-density strain mapping.

2377

Abstract: The phase transformations and the microstructure developments in Fe-Cu base alloys
during isothermal aging are simulated based on the phase-field method. Since the chemical free
energy used in this simulation is obtained from the thermodynamic database of phase diagrams,
the calculated microstructure changes are directly related to the phase diagram of the real alloy
system. Firstly the phase decomposition and the microstructure changes in the Fe-Cu binary alloy
system are demonstrated as the simple example of the phase-field modeling, i.e., the phase
decomposition in bcc phase where the Cu-rich phase forms, the structural phase transformation
from bcc to fcc phase in the Cu-rich nano-particle, and the shape change of fcc-Cu precipitates
from sphere to rod. Secondly, the phase decomposition in bcc phase of the multi-component alloys
such as the Fe-Cu-X (X=Mn,Ni) ternary system and the Fe-Cu-Mn-Ni quaternary alloy is
simulated. At the early stage of aging, the Cu-rich zone with bcc structure begins to nucleate, and
the component X (=Mn, Ni) is partitioned to the Cu-rich phase. When the Cu composition in the
precipitate reaches equilibrium, the component X inside the precipitates moves toward to the
interface region between the precipitate and matrix. Finally, there appears the shell structure that
the Cu precipitates surrounded by the thin layer with high concentration of component X.

2383

Abstract: The thermodynamic assessment of the Al-Ir binary system, one of the key sub-systems of
the Ir-based alloys, was performed using the CALPHAD technique. The AlIr(B2) phase was
described using the two sublattice model with the formula (Al,Ir)0.5(Ir,Va)0.5, while other
intermetallic phases were treated as stoichiometric compounds. The calculated data of the phases in
the Al-Ir system can be used to accurately reproduce experimental data, such as phase equilibria,
invariant reactions, and formation enthalpies of the intermetallic phases.

2389

Abstract: Our recently proposed calculating method reliably predicts the nucleation free energy
barrier of the homogeneous and coherent precipitations. Helmholtz free energy change is clearly
defined and calculated by the purely enthalpic and entropic contributions between the initial state of
the isolated solute atoms scattering around the matrix and the final state of the cluster of size n
traveling around the matrix. The enthalpic term is calculated by the reliable first principles
method and the entropic term is estimated by the ideal solution model. The vibrational free
energy is also included by the quasi-harmonic approximation. The model calculation was
performed on bcc Cu precipitations in the Fe-Cu system. The predicted values of the critical
number of 12 atoms and the critical free energy barrier of 0.6eV show good agreement with the
experimentally estimated ones for the annealing temperature of 773K and the initial concentration
of 1.4at%Cu.

2395

Abstract: One common point amongst extant theories of abnormal grain growth (AGG) is that they
treat this phenomenon in terms of the relative grain size, or grain radius, of the abnormal grains.
Topological and metrical quantities of abnormal grains, such as the number of their faces, or their
grain boundary curvature, are taken into account only indirectly through the grain size itself. This
paper, by contrast, treats AGG in terms of concepts, that include both the boundary curvature and
the number of faces of the abnormal grain. Two cases are examined: 1) AGG, in which the matrix
grains are fully pinned, so normal grain growth cannot occur; 2) AGG in which the matrix grains
are free to evolve, so that normal grain growth ensues simultaneously in the matrix.

2401

Abstract: Thermodynamic assessment of the Al-Cr system has been carried out by incorporating
first-principles calculations into the CALPHAD approach. A regular solution approximation was
adopted to describe the Gibbs energy of the solution phases. The several phases appearing in the
composition range between about 30 and 42 at.%Cr were treated as a single homogeneous γ-phase,
based on recent experimental results, and the Gibbs energy of the γ-phase was represented using the
four-sublattice model with the formula (Al,Cr)8(Al,Cr)8(Cr)12(Al)24. The calculated results enable the
reproduction of experimental results on both the phase equilibria and thermochemical properties. In
addition, a B2 ordered bcc phase, which was suggested to form as an equilibrium phase in a previous
X-ray diffraction study, is not likely to form in either the stable state or metastable state based on our
first-principles calculations.

2407

Abstract: A thermodynamic analysis of the Fe−M−P (M = Nb, Ti) ternary system has been
performed by combining first-principles calculations with the CALPHAD approach. Because of the
lack of experimental information available, thermodynamic properties of orthorhombic
anti-PbCl2-type FeMP were evaluated using the Full Potential Linearized Augmented Plane Wave
method, and the estimated values were introduced into a CALPHAD-type thermodynamic analysis.
Applying this procedure, the phase diagrams of the Fe−M−P ternary phase diagrams whose contents
are uncertain so far were calculated with a high degree of probability. Phase diagrams for high-purity
ferritic stainless steels obtained following the same procedure are also presented.

2413

Abstract: Modeling of Glass transition is attempted based on the Cluster Variation Method. Free
energy functional of an L10 ordered phase is employed to describe the first order nature of the
transition. Free energy contour surface calculated as a function of temperature and an order
parameter which simulates an amount of defects provides a generalized stability diagram in which
the ideal glass transition temperature is identified as a critical point. Transition kinetics is
investigated by Path Probability Method which is the kinetics version of the CVM to time domain.
Continuous cooling behavior is calculated by explicitly incorporating the temperature dependent
viscosity term based on VFT (Vogel-Fulcher-Tamman) formula. The glass transition is realized as
the freezing of the order parameter due to the enhanced viscosity. The extension of the present
theoretical scheme to non-Bravais lattice is attempted by Continuous Cluster Variation Method.

2425

Abstract: Precipitates are the key ingredient for the strength of heat treatable alloys. To optimize
the mechanical properties of alloys it is important to know the response of precipitates to thermomechanical
treatments. In the past, application of computer models to describe the evolution of
precipitates in the course of these processes has proven difficult due to the complexity of the
problem. In this work, a new model based on a mean-field representation of precipitates in a multicomponent
matrix is applied to heat treatments of steels. Example simulations are presented for a 9-
12% Cr ferritic/martensitic heat resistant steel for power plant application and a complex tool steel
with both carbides and intermetallic phases using the software MatCalc. The predictions of the
model are verified on experimental results and the potential application to industrial heat treatment
simulation is discussed.

2431