Mechanical characterization of alumina coatings on C35 steel

C35 steel substrates were alumina-coated via thermal plasma spraying. Before coating, the steel surface was either sandblasted, or pre-oxidized in CO2. The pre-oxidized samples exhibited coatings adhesions of 82±7MPa, and only 45±4MPa for the sandblasted ones. This good result was attributed to the “crystallographic bonding”, which is characterized by the structural continuity of the chain: steel/α-Fe/wüstite/magnetite/γ-Al2O3. The adhesion measurements were obtained utilizing the new technique of the “silver print test” that consists in the painting of a part of the samples surface before coating. The rupture of the coatings occurred at the surface of the substrate, or inside the wüstite layer. •The new process “crystallographic bonding” gives excellent adhesion for the coatings.•Adhesion of alumina coatings on steel C35 reaches 85±7MPa.•This value was measured by the test ASTM C633-01 by using the “silver print test”.•The rupture of the coating occurs between the substrate and the wüstite interlayer.