Crack Paths 2012

Fatigue Crack Paths in Cast Inconel 713LC with/without

Al Diffusion Coating under Various Loading and

TemperatureConditions

J. Pokluda1, K. Obrtlík2, K. Slámeþka1, J. Horníková1, S. Pospíšilová1,

M.Kianicová3 and T. Podrábský1

1 Faculty of Mechanical Engineering, Brno University of Technology, Technická 2,

CZ-61669 Brno, Czech Republic, pokluda@fme.vutbr.cz

2 Institute of Physics of Materials, Academy of Sciences of the Czech Republic,

Žižkova 22, CZ-61662, Czech Republic, obrtlik@ipm.cz

3 Faculty of Industrial Technologies of Púchov, Alexander Dubþek University of

Trenþín, I. Krasku 491/30, SK-02001 Púchov, Slovakia, kianicova@tnuni.sk

ABSTRACT.Fatigue crack paths in cast Inconel 713LC with and without Al diffusion

coating were studied under various loading and temperature conditions. Both coated

and uncoated specimens were fatigued under symmetric bending, symmetric torsion and

in-phase bending-torsion loading at room temperature and under a fully reversed

push-pull straining at 800 °C. Optical and scanning electron microscopy was used to

study fracture surfaces and polished sections cut parallel to the specimen axis. The

image analysis software was employed to determine the percentage of carbides on both

the fracture surfaces and etched specimen sections. Unlike in the case of torsion

loading, an accelerated crack nucleation took place at the particle/matrix interface

within the diffusion coating in the case of both bending loading and push-pull straining.

On the other hand, the final fracture of all tested specimens followed carbides located

at grain boundaries and in inter-dendritic areas.

I N T R O D U C T I O N

Turbine blades of aircraft engines are the most loaded parts of the engine owing to the

high working temperature (about 800°C) and mechanical stresses induced by forces and

moments. Both cyclic and centrifugal forces act on each blade and temperature of

incoming gases can increase by about 500 °C during a few seconds and relevant

temperature gradient can results in elasto-plastic straining. These components must

withstand such a complex loading for a required performance and life-time. They are

often made from layered material systems in which interfaces between layers play a key

role for a prediction of durability. Each layer has different thermal and mechanical

properties. Protective coatings for turbine blades were developed to serve as physical

barriers between aggressive environment and the substrate [1]. For example, diffusion

aluminium coatings (DAC) are based on the intermetallic compound -NiAl that forms

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