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Reliability of interfaces in newly designed ceramic-ceramic and metal-ceramic systems

: Schönholz, R.; Kleer, G.; Döll, W.
: Fraunhofer-Institut für Werkstoffmechanik -IWM-, Freiburg/Brsg.

Freiburg/Brsg., 1990
Wissenschaftlicher Bericht - Fraunhofer-Institut für Werkstoffmechanik, W 3/90
Fraunhofer IWM ()
crack propagation; interface; joining; laminating; plasma spraying; reliability; SiSiC; strength behaviour; stress intensity factor; thermal barrier coating; Weibull distribution; zirconia

The experimental work was performed to investigate the joining of SiSiC, and the reliability of interfaces of laminated SiSiC and of plasma sprayed zirconia base coatings. For SiSiC different process steps of the diffusion bonding technique were investigated and optimized. Tensile, 4-point bending, and double torsion experiments were performed on laminated SiSiC. From these investigations it was found that the interface and sheet orientations determine a non-isotropic strength distribution in this material. In double torsion experiments the influence of the different interface configurations on the macrocrack propagation in laminated SiSiC was investigated. The highest crack resistance was observed when the crack was propagating towards the interfaces perpendiculary. The long term reliability was tested by four point bending fatigue loading up to 10 high 7 cycles. In order to characterize the fracture mechanics behaviour of ceramic coatings on metallic substrates four experimental tech niques with different specimen types were elaborated. Investigations on adhesion strength were performed on tensile specimens. In ZrO thermal barrier coatings the influence of substrate heating during deposition on the properties of the coatings was investigated. A special temperature-time profile leads to K sub IC factors up to 1,5 MNm high -3/2. Service simulation tests performed on a test rig by CSM revealed a clear correlation between the observed failure behaviour and the measured crack resistance.