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Al2O3-TiO2 coatings deposition by intermixed and double injection SPS concepts

Monika Nowakowska
Monika Nowakowska
, 
Paweł Sokołowski
Paweł Sokołowski
, 
Tomáš Tesař
Tomáš Tesař
, 
Radek Mušálek
Radek Mušálek
 et 
Tomasz Kiełczawa
Tomasz Kiełczawa
   | 29 avr. 2022
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Publié en ligne: 29 avr. 2022
Pages: 599 - 614
Reçu: 08 févr. 2022
Accepté: 30 mars 2022
DOI: https://doi.org/10.2478/msp-2021-0046
Mots clés
© 2021 Monika Nowakowska et al., published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Fig. 1

NiCr bond coat powder: morphology (a) and particle size distribution (b)
NiCr bond coat powder: morphology (a) and particle size distribution (b)

Fig. 2

Carousel with AT3_i coatings after spraying
Carousel with AT3_i coatings after spraying

Fig. 3

Temperature of the AT3_di samples recorded with a thermocouple and an IR camera
Temperature of the AT3_di samples recorded with a thermocouple and an IR camera

Fig. 4

Morphology of the Al2O3 (a) and TiO2 (b) powders
Morphology of the Al2O3 (a) and TiO2 (b) powders

Fig. 5

Particle size distribution of the Al2O3 (a) and the TiO2 (b) powders
Particle size distribution of the Al2O3 (a) and the TiO2 (b) powders

Fig. 6

Relationships between the shear rate and the viscosity of the intermixed (a, b) and the non-intermixed suspensions (c, d)
Relationships between the shear rate and the viscosity of the intermixed (a, b) and the non-intermixed suspensions (c, d)

Fig. 7

Values of pH of the studied suspensions
Values of pH of the studied suspensions

Fig. 8

Sedimentation of the suspensions
Sedimentation of the suspensions

Fig. 9

Fragmentation of the suspension in the plasma jet: AT3_i (a), AT3_di (b), AT13_i (c), AT13_di (d), AT40_i (e), AT40_di (f)
Fragmentation of the suspension in the plasma jet: AT3_i (a), AT3_di (b), AT13_i (c), AT13_di (d), AT40_i (e), AT40_di (f)

Fig. 10

Fragmentation of the AT40_di suspension in the plasma jet prior 1 spray cycle (a), after 15 cycles (b), after 30 cycles (c), and after 45 cycles (d) of the deposition
Fragmentation of the AT40_di suspension in the plasma jet prior 1 spray cycle (a), after 15 cycles (b), after 30 cycles (c), and after 45 cycles (d) of the deposition

Fig. 11

Topography of the deposited coatings: AT3_i (a), AT3_di (b), AT13_i (c), AT13_di (d), AT40_i (e), AT40_di (f)
Topography of the deposited coatings: AT3_i (a), AT3_di (b), AT13_i (c), AT13_di (d), AT40_i (e), AT40_di (f)

Fig. 12

Cross-section SEM images: AT3_i (a), AT3_di (b), AT13_i (c), AT13_di (d), AT40_i (e), AT40_di (f)
Cross-section SEM images: AT3_i (a), AT3_di (b), AT13_i (c), AT13_di (d), AT40_i (e), AT40_di (f)

Fig. 13

Phase composition of feedstock powders and deposited coatings
Phase composition of feedstock powders and deposited coatings

Fig. 14

Correlation between the TiO2 content, injection manner, and the growth rate of the coatings
Correlation between the TiO2 content, injection manner, and the growth rate of the coatings

Characteristic of suspensions used for the Al2O3-TiO2 coatings deposition

Coating code Target composition Used suspensions Solvent
AT3_i Al2O3 + 3 wt.% TiO2 intermixed Al2O3 and TiO2, to have Al2O3 + 3 wt.% TiO2 H2O
AT3_di Al2O3 + 3 wt.% TiO2 Al2O3 TiO2 H2O
AT13_i Al2O3 + 13 wt.% TiO2 intermixed Al2O3 and TiO2, to have Al2O3 + 13 wt.% TiO2 H2O
AT13_di Al2O3 + 13 wt.% TiO2 Al2O3 TiO2 H2O
AT40_i Al2O3 + 40 wt.% TiO2 intermixed Al2O3 and TiO2, to have Al2O3 + 40 wt.% TiO2 H2O
AT40_di Al2O3 + 40 wt.% TiO2 Al2O3 TiO2 H2O

Deposition parameters of bond coat

Substrate austenitic stainless steel AISI 304/1.4301, 3 mm thick, diameter 25 mm; sand blasted before spraying (F36 grit, 500–600 μm mesh size) and sonicated with ethanol
Powder NiCr 80-20, Amdry 4535; dried 3 h before spraying at 110°C
Electric power 27 kW
Injection radial, external
Stand-off distance 100 mm
Gun SG-100, Praxair, Indianapolis, USA
Feeding 15 g/min
Transverse velocity 400 mm/s
Plasma gases Ar/H2: 45/5 slpm
Carrier gas Ar 3.5 slpm

Deposition parameters and thickness of top coat

AT3_i AT3_di AT13_i AT13_di AT40_i AT40_di
Injection angle, ° 25 25 25 25 25 25
Feeding distance, mm 25 25 25 25 25 25
Stand-off distance, mm 100 100 100 100 100 100
Nozzle diameter, mm 0.35 2×0.2 0.35 2×0.2 0.35 2×0.2
Robot speed, mm/s 30 30 30 30 30 30
Carousel speed, RPM 55.5 55.5 55.5 55.5 55.5 55.5
Torch amperage, A 500 500 500 500 500 500
Torch power, kW 150 150 150 150 150 150
Feeding liquid rate, g/min 120 2×37 120 2×37 120 2×37
Feeding pressure, MPa 0.35 0.24 0.35 0.24 0.35 0.24
Interpass substrate temperature, °C 250 250 250 250 250 250
Preheating yes yes yes yes yes yes
Active cooling air air air air air air
Number of deposition cycles 40 140 40 120 40 100
Total number of deposition passes 120 420 120 360 120 300
Net spraying time, min 9.3 32.7 9.3 28 9.3 23.3
Coating thickness, μm 338.2±16.9 241.5±8.2 360.9±16.7 296.7±5.8 316.2±10.9 287.6±8.4
Normalized growth rate, μm/pass 2.82±0.14 1.74±0.06 3.01±0.14 2.24±0.05 2.63±0.09 1.80±0.06

Comparison of the double injection and intermixed spraying

Property Double injection Intermixed suspension
feedstock stability + easier prevention of agglomeration and sedimentation of two feedstocks separately − stability of a mixture (suspension/suspension; suspension/powder; suspension/solution precursor) may not be easily guaranteed
waste + minimized material loss – the suspension after spraying can be further stored and easily used for the next spraying − waste remains, initial suspensions cannot be separated and used again
spraying comprehensiveness + it opens up the possibility for a precise control of the particle thermal history, the microstructure and phase composition of coatings− the need for independent and time-consuming optimization of two feeding/injection lines – the spraying distance, angle, etc. have to be adjusted separately + easier optimization of spraying parameters for the injection of a single liquid
tailoring of chemical composition − difficult selection of suspension/solvent/powder/dispersing agents concentrations (especially when strong dilution is needed) + easy tailoring of the feedstock chemical composition
sprayability − spraying is difficult in the case of low constituent content – there is a need to intensively dilute the suspensions; consequently, lots of energy is consumed for solvent evaporation, leading to a low process efficiency; + feasibility of the process + the ratio of the feedstock composition may be easily adjusted, so the disadvantages of the double injection are easily omitted
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