Crack Paths 2012

C O N C L U S I O N

In the low cycle fatigue domain, the presence of the coating slightly decreases the

fatigue resistance to room-temperature bending as well as to high-temperature push-pull

tests. Conversely, it increases the torsion resistance at room temperature. The different

bending/push-pull and torsion response is caused by different fatigue crack initiation

micromechanisms. In the first case, an accelerated crack nucleation takes place at the

particle/matrix interface within the diffusion coating, while, in the latter case, the role of

the secondary phase particles is diminished due to a much lower normal loading

component. Whenthe combined bending-torsion loading with

a § τa is applied, the

bending component is dominant since the initiation micromechanism is also controlled

by particle/matrix decohesion and, therefore, the fatigue life of D A Cspecimens is

slightly lower. In all the accomplished tests, the main crack path in the specimen bulk

coincides with carbides located at the interdendritic regions. In summary, the observed

differences between the fatigue life of coated and uncoated specimens are rather minor.

Consequently, one can assume that the deposition of the coating on turbine blades will

lead to a longer service life of these components since the coating substantially

improves the high-temperature oxidation and corrosion resistance of blades.

A C K N O W L E D G E M E N T

The authors acknowledge the financial support provided by the Czech Science

Foundation in the frame of the projects P108/12/0144, P107/11/2065 and P107/12/1922.

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