C. Toffolon-Masclet,
1
J. C. Brachet,
1
C. Servant,
2
J. M. Joubert,
3
P. Barberis,
4
N. Dupin,
5
and
P. Zeller
6
Contribution of Thermodynamic Calculations to Metallurgical
Studies of Multi-Component Zirconium Based
Alloys
ABSTRACT: The Zircobase thermodynamic database for zirconium alloys coupled with Thermo-Calc soft-
ware represents a powerful tool for prediction of thermodynamic and metallurgical data such as activities,
formation enthalpies, phase transformation temperatures, solubility limits, existence temperature range,
and chemical compositions of second phase precipitates. This database was built up with binary and
ternary descriptions assessed according to the CALPHAD methodology. It is sometimes necessary to take
into account new systems, but also new versions of binary descriptions as recently experienced. For
example, the two binary systems Zr-Fe and Zr-Sn had to be updated in order to fit new experimental results
believed to be more accurate than previously available.This paper aims at showing the improvements of
the database taking into account new descriptions of binary systems, as also ternary description such as
Zr-Fe-Cr, Zr-Fe-Ni, and Zr-Nb-Fe. For this last ternary system, new experimental data were necessary.
New experimental study of the two ternary phases, hexagonal ZrNb,Fe
2
and cubic Zr,Nb
4
Fe
2
, allowed
their crystal structures P6
3
/mmc and Fd3
¯
m, respectively to be checked. This was useful to build up a
sublattice model giving account of the existence of a composition range for these two intermetallic phases.
Moreover, several specific ZrNbFe alloys were fabricated and annealed for times ranging from 1000 h to
10,000 h at 550, 700, 800, and 900°C to determine the equilibrium binary and ternary phase domains as a
function of the temperature. All these data were used to obtain an improved thermodynamic modelling of
this system. Finally, we illustrate some thermodynamic predictions of the different phases evolutions as a
function of the temperature on multi-alloyed industrial type alloys. These examples show quite good agree-
ment between the thermodynamic predictions and the experimental data derived from calorimetric experi-
ments and microstructural observations.
KEYWORDS: Zircobase, Zr-Sn, Zr-Nb-Fe, ZrNb,Fe
2
intermetallic phase, Zr,Nb
4
Fe
2
intermetallic
phase, Zr-Fe-Cr, Zr-Fe-Ni, Thermo-calc
Introduction
These last years, the development of computational thermodynamics has been of very high interest for
industrial applications. Indeed, materials development, process control, weldability, fabrication, in-service
and accidental conditions imply the development of large databases able to take into account multi-
component systems representative of the industrial alloys and interactions with oxygen and hydrogen due
to intermediate and high temperature oxidation phenomena. In this framework, the Zircobase, thermody-
namic database for zirconium alloys 1, has been created and keeps evolving by taking into account new
binary and ternary systems or by the revision of already existing binary systems.
The aim of this article is to present the recent improvements which allowed proposing a new version
of the Zircobase. For this, the so-called CALPHAD technique has been applied in order to take into
account the Zr-Nb-Fe ternary system in the Zircobase.
In a first part, the recent improvements obtained on the Zr-Sn binary system are presented, more
particularly, we present how the combination of experimental investigations and first-Principles calcula-
Manuscript received March 12, 2007; accepted for publication April 21, 2008; published online July 2008.
1
CEA/DEN, Nuclear Materials Department, CEA/Saclay, F-91191 Gif-sur-Yvette, France, e-mail: caroline.toffolon@cea.fr
2
LPCES, Université Paris-Sud, F-91405 Orsay, France.
3
CMTR, ICMPE, CNRS UMR 7182, F-94320 Thiais, France.
4
AREVA, CEZUS Research Center,Avenue Paul Girod, F-73403 Ugine Cedex, France.
5
CALCUL THERMODYNAMIQUE, 3 rue de l’avenir, F-63670 Orcet, France.
6
CEA/DEN, Physico-Chemistry Department, CEA/Saclay, F-91191 Gif-sur-Yvette, France.
Journal of ASTM International, Vol. 5, No. 7
Paper ID JAI101122
Available online at www.astm.org
Copyright © 2008 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.