Multilayer SiBCN/TiAlSiCN and AlOx/TiAlSiCN coatings with high thermal stability and oxidation resistance

Abstract

In this work we utilized a multilayer approach to achieve extremely high thermal stability and oxidation resistance without compromising the coating hardness. Multilayer SiBCN/TiAlSiCN and AlOx/TiAlSiCN coatings were deposited by magnetron sputtering of TiAlSiCN target and ion sputtering of either SiBC or Al2O3 targets. To investigate thermal stability and oxidation resistance, samples were annealed in vacuum at 1000, 1300, and 1400°C and in air at 1000 and 1100°C for 1h. After vacuum annealing at 1300°C, the AlOx/TiAlSiCN coatings lost multilayer structure due to crystallization of AlOx layers and significant grain growth within the TiAlSiCN layers, which was accompanied by Si loss, and h-AlN precipitation. In contrast, the SiBCN/TiAlSiCN samples annealed at 1300°C completely preserved their multilayer structure. After 1400°C, recrystallization of the SiBCN/TiAlSiCN coating was only observed to occur in several upper layers, whereas other part of the coating retained its initial microstructure. Hardness of the SiBCN/TiAlSiCN and AlOx/TiAlSiCN coatings increased from 34 and 24GPa to 40 and 30GPa at 1000°C and then decreased to 27 and 15GPa at 1300°C, respectively. The incorporation of AlOx and SiBCN interlayers into the TiAlSiCN coatings was shown to significantly improve their oxidation resistance. After 1100°C, the AlOх/TiAlSiCN coatings were only partially oxidized (about 35% of the total coating thickness). Lowermost layers in the SiBCN/TiAlSiCN coatings after annealing at 1100°C were not affected by oxidation as well. Finally, mechanism and kinetics of oxidation are discussed.