Sandwich specimens were prepared by firing a thin inter-layer of porous
La0.6Sr0.4Co0.2Fe0.8O3-d (LSCF) to bond a thin tetragonal yttria-stabilised
zirconia (YSZ) beam to a thick YSZ substrate. Fracture of the joint was
evaluated by introducing a wedge between the two YSZ adherands so that the
stored energy in the thin YSZ cantilever beam drives a stable crack in the
adhesive bond and allows the critical energy release rate for crack extension
(fracture toughness) to be measured. The crack path in most specimens showed a
mixture of adhesive failure (at the YSZ-LSCF interface) and cohesive failure
(within the LSCF). It was found that the extent of adhesive fracture increased
with firing temperature and decreased with LSCF layer thickness. The adhesive
failures were mainly at the interface between the LSCF and the thin YSZ beam
and FEM modelling revealed that this is due to asymmetric stresses in the LSCF.
Within the firing temperature range of 1000-1150C, the bonding fracture
toughness appears to have a strong dependence on firing temperature. However,
the intrinsic adhesive fracture toughness of the LSCF/YSZ interface was
estimated to be 11 Jm2 and was not firing temperature dependent within the
temperature range investigated.Comment: 13 figures, 1 table, journal paper publishe
