PSI - Issue 10

I. Georgiopoulos et al. / Procedia Structural Integrity 10 (2018) 280–287 I. Georgiopoulos et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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Plasma power: 56 kW, Feed rate: 21.8 ml/min, Atomization gas flow rate: 12 slpm

Plasma power: 56 kW, Feed rate: 10 ml/min, Atomization gas flow rate: 12 slpm

Plasma power: 50 kW, Feed rate: 10 ml/min, Atomization gas flow rate: 12 slpm

Plasma power: 50 kW, Feed rate: 10 ml/min, Atomization gas flow rate: 15 slpm

Fig. 4. SEM cross sections of LaAlO 3 SPPS deposited coatings with different sets of plasma spray parameters.

Furthermore the applied plasma power effect showed that power increase results in higher quality microstructure (Fig. 3b, c) as well as deposition rate from 5 to 20 μm/pass and process yield from 35 to 45%. Investigation of the effect of the atomization gas flow rate on the deposited LaAlO 3 coatings revealed that increase of the flow rate results in a maximum deposition rate of 7 μm/pass and maximum process yield 60% at the flow rate value of 15 slpm. By the X ray diffraction results the phase composition of the deposited coatings under the selected sets of plasma spraying parameters investigated, revealed the formation of LaAlO 3 phase as the predominant crystal phase (Statho poulos et al. (2018)). The coating shows only traces of La as a secondary phase (Fig. 5). This is a very important result since it confirms the advantage of the SPPS coating deposition as a single step technique towards the formation of LaAlO 3 oxide without the need of post annealing. In the minimum time of the liquid feedstock precursor material flight within the high temperature plasma flame all required chemical synthesis steps occurs. Thus the citrate-precursor La – Al compounds form a high purity LaAlO 3 oxide as a deposited coating.

Fig. 5. XRD patterns of the LaAlO 3 coatings deposited using SPPS technique under the sets of parameters as described in Fig. 4.

3.2. Multi-layered TBC development and characterization

Thermal spray deposition parameters optimization of the above mentioned investigated materials as two-layered (top coat-bond coat) systems, was followed by the deposition and characterization of three layered systems (over coat- top coat-bond coat) as shown in Table 1 and Fig. 6.