Crack Paths 2012

under the influence of the substrate, usually the cast Ni-superalloy. Besides a high

temperature oxidation and corrosion, the most serious degradation modes are

mechanical fatigue under bending-torsion loading and creep at high temperatures [2].

This study is focused on fatigue crack paths under symmetric bending, symmetric

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

push-pull straining at 800 °C in cast Ni-superalloy Inconel 713LC with and without

DAC.The influence of microstructure on fracture morphology is documented and the

fatigue resistance under various loading and temperature conditions is obtained. The

present work is a part of more complex research on the effect of surface treatment on

the fatigue behaviour of cast nickel-base superalloys [3-5].

E X P E R I M E N T A L

All studied specimens were produced from rods cast of the same Inconel 713LC

(IN713LC) batch (denoted as B38) by the company PBS Velká Bíteš, a.s, Czech

Republic. The nominal chemical composition is shown in Tab. 1. The specimens were

coated by D A Cusing the out-of-pack method at the Politechnika lska Katowice,

Poland. Specimens for biaxial fatigue experiments were then heat treated at the

temperature 950 C for 5 hours. Substrate from IN713LCwas of a dendritic structure

with small cast defects. The average grain size was 2.3 mm. The microstructure

contained cuboidal ´precipitates (Ni3Al, Ni3AlTi) embedded in the matrix and

complex carbides. The microstructure and thickness of coating were studied by light

microscopy with image analyses software. The chemical spot and plane analyses of

coating were performed using the energy dispersion X-ray spectrometer E D A Xbuilt in

the scanning electron microscope (SEM) Philips XL30 and the microhardness was

measured by indentation tester L E C O400M-PC2. Fracture surfaces of selected

specimens were investigated in S E Malong with sections of the gauge segments cut

parallel to the specimen axis. The carbide fraction and the average size of carbides were

determined by image analyses software.

Tab. 1 The nominal chemical composition of IN713LCin wt. %

Cr Al M o Nb Ti Zr C B P S Ni

[wt.%] 11.85 5.8 4.54 2.27 0.72 0.11 0.04 0.015 0.006 0.004 bal.

The aluminium coating consists of an outer layer (OL) and a diffusion zone (DZ), see

Fig. 1. The average total thickness of the coating and the D Zwas 72 m and 22 m,

respectively. The averaged microhardness of D A Cwas about two times higher than that

of the substrate. The microstructure of O Lconsists of the phase (NiAl) with small

number of complex phases and carbides Al-Cr-Ni, Mo-Cr-Nb. The D Z is formed by

phase Ni-Al with manyCr-Mo, Mo-Cr-Nbrich particles.

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