Correlation between thermal fatigue and thermomechanical properties during the oxidation of multilayered TiSiN nanocomposite coatings synthesized by a hybrid physical/chemical vapour deposition process

Abstract

TiSiN and TiSiAlN coatings were deposited on M2 steel by a hybrid physical/chemical vapour deposition process. SiH 4 was used as precursor for Si, while metals were brought by arc evaporation. This hybrid process allowed us to control the silicon enrichment along the coating thickness. Both films were synthesized applying a serrated silane partial pressure during deposition, leading to a multilayered structure with a 700 nm period. X-ray diffraction analyses showed only TiN peaks, whose width revealed a mean grain size below 10 nm. The multilayer structure and the nanometric size of the grains in layers containing a high Si content were observed by cross-section microscopy in transmission mode. Mechanical properties were improved compared to both TiN and SiN x references, in relation to the nanocomposite microstructure of layers enriched in silicon. The oxidation behaviour was assessed by thermogravimetric analyses. The oxidation resistance was studied in isothermal, dynamic as well as cycling (10-cycle runs 25–800–25 °C) conditions. The multilayered nanocomposite TiSiN film exhibited a high durability in terms of mechanical and oxidation behaviours. Thermal cycling experiments revealed its high resistance which seems to result from a synergy between the shield effect of the SiN x network — that would limit the oxidation process — and the intrinsic “deformability” of TiN layers — that would withstand the volume modifications of the substrate due to temperature variations. A further addition of aluminium, without significantly affecting the mechanical properties, contributes to the improvement of the oxidation resistance thanks to the formation of the expected outer refractory alumina layer.