Journal of the European Ceramic Society 26 (2006) 2699–2705
Piezo-spectroscopic characterization of alumina-aluminium
titanate laminates
Goffredo de Portu
a,d
, Salvador Bueno
b
, Lorenzo Micele
a,d
,
Carmen Baudin
b,∗
, Giuseppe Pezzotti
c,d
a
Institute of Science and Technology for Ceramics, ISTEC-CNR, Via Granarolo, 64-48018 Faenza, Italy
b
Instituto de Ceramica y Vidrio, CSIC-Campus de Cantoblanco, Kelsen 5, 28049 Madrid, Spain
c
Ceramic Physics Laboratory, Kyoto Institute of Technology, KIT, Sakyo-ku, Matsugasaki, 606-8585 Kyoto, Japan
d
Research Institute for Nanoscience, RIN, Sakyo-ku, Matsugasaki, 606-8585 Kyoto, Japan
Received 19 March 2005; received in revised form 30 June 2005; accepted 8 July 2005
Available online 13 September 2005
Abstract
A multilayered alumina-aluminium titanate composite was prepared by a colloidal route from aqueous suspensions. The structure of the
laminate was symmetric and constituted of two external Al
2
O
3
layers (width
∼
= 1750 m), one central Al
2
O
3
layer (width
∼
= 1200 m) and
two intermediate thin (width
∼
= 315–330 m) Al
2
O
3
–Al
2
TiO
5
layers.
Additional monolithic materials with the same compositions as those of the layers were fabricated as reference materials. Young’s modulus
of the monoliths was determined by three point bending. Dilatometry determinations were performed on green specimens, following the same
heating and cooling schedules as those used for sintering the laminate, in order to determine the actual dimensional changes on cooling after
sintering. The dimensional changes of the sintered specimens on heating and on cooling were also determined. Microscopic distributions
of residual stresses were evaluated by fluorescence piezo-spectroscopy, and they revealed the existence of weak tensile and compressive
hydrostatic stresses in the aluminium titanate and alumina layers, respectively. The level and sign of these stresses was in good agreement
with those predicted based on analysis of the Young’s modulus and the dimensional variations during cooling after sintering of the monoliths
with the same compositions as those of the layers. Dimensional variations during cooling after sintering were different from those for sintered
materials, which presented hysteresis between heating and cooling. In spite of the presence of compressive residual stresses in the external
layers of the laminate, strength values of notched samples of the laminated specimens were lower than those for monoliths of the same
composition as the external layers.
© 2005 Elsevier Ltd. All rights reserved.
Keywords: Laminates; Spectroscopy; Thermal expansion; Al
2
O
3
; Al
2
TiO
5
1. Introduction
Alumina (Al
2
O
3
)–aluminium titanate (Al
2
TiO
5
) com-
posites can offer improved flaw tolerance and toughness.
1–7
Toughening in this system is originated by the residual
stresses developed, during cooling from the sintering
temperature, due to the thermal expansion mismatch
between alumina (α
i25–1000
◦
C
= average thermal expan-
sion coefficient between 25 and 1000
◦
C in the axis i,
∗
Corresponding author. Tel.: +34 91 7355840; fax: +34 91 7355843.
E-mail address: cbaudin@icv.csic.es (C. Baudin).
α
a25–1000
◦
C
= 8.4 × 10
-6 ◦
C
-1
, α
c25–1000
◦
C
= 9.2 × 10
-6 ◦
C
-1
)
8
and aluminium titanate (α
a25–1000
◦
C
= 10.9 ×
10
-6 ◦
C
-1
, α
b25–1000
◦
C
= 20.5 × 10
-6 ◦
C
-1
, α
c25–1000
◦
C
=
-2.7 × 10
-6 ◦
C
-1
).
9
As the toughening mechanisms that
have been identified in these composites are crack bridging
and microcracking,
6,7
toughening is often associated with
low strength.
Laminated materials are being investigated as means to
combine strength and toughness in ceramic materials.
10
As
an example, Russo et al.
11
proposed structures formed by lay-
ers of equal compositions, made of mixtures of alumina and
aluminium titanate, and dissimilar microstructures. In partic-
0955-2219/$ – see front matter © 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jeurceramsoc.2005.07.060