A two-level factorial and a central composite design have been employed to study the effect of fuel flow, oxygen flow and spray distance on the properties residual stress, porosity and oxide content, and deposition efficiency of NiCoCrAlY coatings.
The results suggest a correlation between the fuel and the oxygen ratio flow, and the porosity and oxide content on the coatings based on the interaction between particle and the flame (its power and chemistry). Using fuel-rich flames results in coatings with low porosity and oxidation, low residual stresses, and high deposition efficiency due to the high velocity and low temperature attained by the particles.
The two-level factorial design results show that the spray distance has a large influence on the residual stresses and deposition efficiency, while the porosity and oxide content is dependent not only on spray distance but also on the other two tested variables (oxygen and fuel flows).
Spray distances between 250 and 300 mm produce coatings that are homogeneous, dense, with high intersplat cohesion coatings. At these spray distances, the particles reach their optimal velocity and temperature resulting in a balance of spreading, flattening, and solidification.
Lastly, as an outcome of the central composite DoE, a specific condition was used to deposit a coating considered optimized. Although the predicted and the experimental results for this optimized parameter showed slight differences, a clear evidence of the effectiveness of the optimization procedure is confirmed by the reproducibility of the previous results obtained within the central composite DoE. However, additional studies are required to refine the prediction of the optimization model employed.
Based on the responses of the tested parameters, it can be stated that the methodology enables to attain the optimal spray condition and particle state for NiCoCrAlY deposits with good properties.
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