THERMAL STABILITY OF OXIDE-BASED CERAMIC MATERIALS
I. Yu. Prokhorov
Translated from Ogneupory i Tekhnicheskaya Keramika, No. 5, pp. 37 – 47, May, 2002.
A correlation analysis of the thermal stability of oxide-based ceramic materials (including partially yttria-sta
bilized zirconia (PYSZ), beta-alumina, and titanium dioxide) produced in batches by different technologies is
carried out. A generalized criterion for thermal stability is proposed that takes into account partial compensa
tion of the thermally generated elastic strain owing to compliant behavior of the network of surface cracks.
The criterion provides a satisfactory description of experimental data, allows prediction of the behavior of ma
terials under severe thermomechanical conditions, and suggests ways toward further improvement of material
Thermal stability is one of the most important properties
of materials that determine their serviceability under differ-
ent conditions. Thermal stability is practically always a fac-
tor to be taken into account under high-temperature or mode-
rate-temperature operating conditions. Not infrequently, even
under normal conditions, a local overheat of components
from friction is the only cause of their premature failure.
First and foremost, thermal stability is a matter of serious
concern for brittle nonmetallic materials; in contrast, metals
are less sensitive to thermal shock and are more prone to fai
lure because of corrosion.
Paradoxically, thermal stability has been little studied
and at present there is neither a unique criterion nor a general
method for its determination . A situation has arisen where
neither handbook data  nor research results provide an ad
equate means of comparative evaluation of various materials
and their use for a concrete application — neither estimating
the service life of a given material, nor suggesting a way to
ward its improvement.
In this context, relevant to the problem at hand would be
a study aimed at designing thermal stability criteria applica
ble at least to a part of the vast class of materials [1, 3]. At
present, the following thermal stability criteria developed for
a plane stress state are currently in use:
where s is the tensile stress (under normal conditions), n is
Poisson’s ratio, E is the modulus of elasticity, a is the coeffi
cient of linear expansion, l and a are the heat conductivity
and thermal diffusivity of the material, g is the effective sur
face fracture energy, and K
is the crack resistance. It is as
sumed that criteria R, R
, and R
apply to materials in which
crack nucleation is the main factor that controls fracture, that
is, the materials in question are homogeneous and brittle.
, and T
are used to characterize steady crack
growth in porous and/or microscopically cracked materials
typically represented by traditional refractory materials.
Of the given above equations, the first three have the
physical meaning of maximum thermal stresses associated
with a temperature difference. Correcting for heat conducti
vity in R
or thermal diffusivity in R
makes it possible, in a
first approximation, to take account of the width of a gradient
zone, that is, the sharpness of this temperature difference.
The next two expressions have the meaning of a reciprocal
Refractories and Industrial Ceramics Vol. 43, Nos.5–6, 2002
1083-4877/02/0506-0195$27.00 © 2002 Plenum Publishing Corporation
Donetsk Institute of Engineering Physics (DonFTI), Donetsk,