To develop highly efficient gas turbines, thermal barrier coating syst
ems with a high reliability and a long lifetime under severe operating
conditions are required. The failure of TBC-systems is caused by ther
mal cycling conditions, oxidation attack, and insufficient adhesion at
the interface of the ceramic coating and the bond coat. Coating failu
re occurs mostly near the interface top coat-bond coat. Two modificati
ons of a conventional duplex TBC-system consisting of a Ni-base alloy
substrate/MCrAlY-bond coat/ZrO2 7 wt.% Y2O3-top coat, which is used as
the reference system, are presented as follows. (i) By contouring the
MCrAlY-bond coat with a laser, the stress distribution at the ZrO2-bo
nd coat interface can be modified by forming folds within the laminate
structure of the ceramic top coat and increasing the bonding area. TB
C-systems containing a contoured bond coat show better thermal cycling
behaviour. FEM-simulation of thermally induced stress shows an altern
ating stress distribution which is caused by the contoured bond coat i
nterface. (ii) High-velocity oxygen fuel (HVOF)-sprayed MCrAlY layers
are a new possibility to create homogeneous bond coats. Thermal barrie
r coatings with LPPS-(low pressure plasma sprayed) or HVOF-CoNiCrAlY b
ond coats are compared by investigating their porosity, roughness, and
oxidation behaviour. The porosity is proportional to the roughness of
the HVOF bond coats. The oxide content was examined by TEM and EDX an
alysis. HVOF-CoNiCrAlY bond coats show oxidation behaviour similar to
coatings produced by LPPS. (C) 1997 Elsevier Science S.A.