PSI - Issue 10

I. Georgiopoulos et al. / Procedia Structural Integrity 10 (2018) 280–287

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I. Georgiopoulos et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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Microscope. Coatings porosity was estimated using a Leica microscope and Image Analysis software. Vickers micro hardness measurements on coatings was performed using a Shimadzu micro hardness tester. Thermal cyclic testing (Fig. 2) has been performed on rectangular, one-side coated samples under the following conditions:  Short Cycle: Heat up to 1100 o C or 1200 °C in 16 min; hold at temperature for 1 hour; cool down to room temperature (18 °C) in approximately 50 min.  Long Cycle: Heat up to 1100 o C or 1200 °C in 16 min; hold temperature for 25 hours; cool down to room temperature (18 °C) in approxim ately 50 min. In both cases tests were continued until 10-20% spallation of the TBC area was observed. Total duration (number of cycles) under thermal cycling at 1100 o C and 1200 o C were studied.

Fig. 2. Temperature profile of the thermal cycling testing at 1200 o C (left) short cycle and (right) long cycle.

3. Results and discussion

3.1. Top coat layers deposition parameters optimization

7YSZ layer using SPS: The obtained coating thickness was in the range of 25- 50 μm. Its porosity ranged from 9 to 18% while its microhardness HV100 from 300 to 772. In Fig. 3a &b the microstructure of the optimum coating is shown. Its thickness is 38 μm and from the polished cross section (Fig. 3b) a continuous, homogeneous, microcrack free, without any evidence of delamination coating is revealed. Its microhardness HV100 is 633 and has a porosity of 9% (Fig. 3c).

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b

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Fig. 3. 7YSZ SPS coating (a, b) SEM micrograph of polished cross-section and (c) porosity measurement of this coating through image analysis.

LaAlO 3 layer using SPPS: The effect of critical plasma spray parameters on the quality of the developed coatings has been investigated. In detail, the effect of the solution feed rate on the coating microstructure (Fig. 4a, b) showed that decrease of the feed rate results in higher deposition rate from 7 to 20 μm/pass and increase of the process yield.