Thermal stability of amorphous Ti-B-Si-N coatings with variable Si/B concentration ratio

Due to their homogenous structure without grain boundaries, amorphous nitride-based coatings represent a potentially attractive material for high-temperature applications in aggressive environment. In this article, we report on the thermal stability and mechanical properties of amorphous quaternary Ti-B-Si-N coatings with variable Si/B concentration ratio prepared by reactive magnetron co-sputtering. Biaxial stress temperature measurement was used to evaluate thermal stability of amorphous as-deposited coatings in the region up to 600 °C. The chemical composition of the coatings was stable up to 1100 °C. During the annealing small amount of nanocrystalline fcc-TiN phase (with grain size of 1-4 nm) in amorphous matrix a-(Ti)BSiN was formed. The prevailing BN, SiN and TiN bonds remained also unchanged as observed by X-ray photoelectron spectroscopy. The gradual increase of hardness to maximum at 14 GPa and the overall positive effect on thermal stability was observed with increasing Si/B concentration ratio. The dominating volume of the amorphous phase after annealing had a significant influence on maintaining constant hardness values up to 1100 °C.