Influence of Detonation Gun Spraying Conditions on the Quality of Fe-Al Intermetallic Protective Coatings in the Presence of NiAl and NiCr Interlayers

Abstract

The paper presents results of detailed research of the application of detonation gun (D-gun) spraying process for deposition of Fe-Al intermetallic coatings in the presence of NiAl and NiCr interlayers. A number of D-gun experiments have been carried out with significant changes in spraying parameters which define the process energy levels (changes in volumes of the working and fuel gases, and the distance and frequency of spraying). These changes directly influenced the quality of the coatings. The initial results underlay the choice of the process parameters with the view to obtain the most advantageous of geometric and physical-mechanical properties of the coating material, interlayer and substrate. The metallurgical quality of the coatings was considered by taking into account grain morphology, the inhomogeneity of chemical content and phase structure, the cohesive porosity in the coating volume, and adhesive porosity in the substrate/interlayer/coating boundaries. The surface roughness level was also considered. It was found that the D-gun sprayed coatings are in all cases built with flat lamellar splats. The splats develop from powder particles which are D-gun transformed in their plasticity and geometry. A significant result of the optimization of D-gun spraying parameters is the lack of signs of melting of the material (even in microareas) while the geometry of the subsequently deposited grains is considerably changed and the adhesivity and cohesion of the layers proves to be high. This is considered as an undeniable proof of high plasticity of the D-gun formed Fe-Al intermetallic coating.

Nanocomposite Fe-Al Intermetallic Coating Obtained by Gas Detonation Spraying of Milled Self-Decomposing Powder

“…Oxides are formed during the GDS process, in the stage when the detonation wave propagates through the powder particles, which involves rapid chemical reactions accompanied by the release of a large amount of thermal energy (Ref [18][19][20][21][22][23][30][31][32]. However, despite the high velocity of the detonation wave, the powder particles can partially melt at their surfaces and then quickly oxidize due to the high concentration of free radicals, eventually solidifying on their approach to the substrate ( Ref 28,29,32).…”

Meta-stable Solidification Created by the Detonation Method of Coating Formation

“…A control of the spraying parameters with the objective to obtain coatings with unique exploiting properties like resistance to abrasive wear, erosion, corrosion, high temperature corrosion or thermal shocks, as well as good adhesion and low porosity was the subject of number of works [1][2][3][4][5][6].…”

“…According to some considerations [4], [5], a temperature of particles during the deposition does not exceed the melting point.…”

“…A single particle containing 63 at.% Al is subjected to the detailed analysis, 0 0.63 N = . The particles of the Fe-Al type (63 at.% Al) and less than 50 µm in diameter can be partially melted because of an appearance of a supersonic striking wave, [5], in front of which particles have a powerful kinetic energy while moving with a stream of a high pressure gas.…”

Microstructure characterization of D-gun sprayed Fe–Al intermetallic coatings

“…Iron aluminide-based intermetallic alloys are attractive materials for several industrial applications at medium to high temperatures [1][2][3] both as bulk materials and as coatings because of their good mechanical properties, relatively low density (5.56 g/ cm 3 for the FeAl phase), excellent corrosion resistance in oxidising and sulphidising atmospheres (a result of their ability to form a highly protective Al 2 O 3 scale [3][4][5][6]), and low cost.…”