Gas detonation spray forming of Fe–Al coatings in the presence of interlayer

The present paper reports that gas detonation sprayed (GDS) NiAl and NiCr intermediate layers underneath of the intermetallic Fe–Al type coatings on plain carbon steel substrate form bilayer coating system interacting with external environment and/or metal elements. The interface layers are responsible for hardness, bond strength, thermal stability and adhesive strength of the whole GDS structure. The physical–chemical properties of the intermediate layers, combined with unique, very dense and pore free intermetallic Fe–Al coating obtained from self-decomposing powders resulted in new, beneficial features of the whole GDS structure which became more complex, enabled independent control of its functional properties and considerably reduced negative gradients of stress and temperature influencing the substrate and increasing adhesion strength.The achievement of homogenous and refined structure (comprising of small (< 1 µm) and equiaxed sized grains) creates a thermal barrier based on high-melting point intermetallic phases containing Al2O3 ceramics which is responsible for properties of the GDS bilayer coatings. The application properties were investigated and the specific multilayer structure of the GDS coating was analyzed such as the phase composition, the degree of order, grain morphology, the quality of substrate/interlayer/external coating bonds, and first of all the influence of hardness of the NiAl or NiCr intermediate layers on the hardness and thermal stability of the FeAl coating after gas detonation spraying and additional heating at 750 °C and 950 °C for 10 h.