Thermal Stability of Oxidation-Resistant Ta-Zr-Si-B-N and Ta-Zr-Si-B-C Coatings under In Situ TEM Heating and Vacuum Annealing

Amorphous Ta-Zr-Si-B-C and Ta-Zr-Si-B-N coatings were deposited by magnetron sputtering using a ceramic target in Ar + C2H4 and Ar + N2 reaction media. Thermal stability under in situ TEM heating, vacuum annealing and nanoindentation, as well as the effect of heating on structural-phase transformations in coatings and their mechanical characteristics, have been studied. The results showed that the heating of amorphous Ta-Zr-Si-B-C and Ta-Zr-Si-B-N coatings in a TEM column leads to precipitation h-TaSi2 and c-TaC crystalline phases at a temperature of 600 °C and h-Ta5Si3 and c-TaN at a temperature of 1000 °C, respectively. Similar structural-phase transformations were revealed as a result of vacuum annealing. An increase in temperature from 20 to 1000 °C led to a decrease in the hardness of the carbon-containing coating from 21 to 16 GPa as a result of stress relaxation. For the Ta-Zr-Si-B-N coating at a temperature of 1000 °C, an increase in hardness was observed from 18 to 27 GPa, which is associated with the crystallization of the coating, with the formation of a nanocomposite structure with h-Ta5Si3 and c-TaN crystallites of 6–10 nm in size and an a-Si(Zr,B)N amorphous region.