Hf-B-Si-C-N films fabricated using reactive pulsed dc magnetron co-sputtering are hard, optically transparent, and exhibit superior high-temperature oxidation resistance. In this work, we have conducted a systematic and detailed microstructural analysis of the as-deposited Hf7B23Si22C6N40 and Hf6B21Si19C4N47 films and the annealed films up to various temperatures from 1100 °C to 1600 °C in air and in helium using HRTEM. The motivation for this research was to understand the behavior of the high temperature oxidation resistance by studying their microstructure evolution as a function of their exposure to high temperatures in view of their slight change in composition. The overall objective is to respond to the need for thin-film materials for severe environment applications which can resist corrosion and oxidation at elevated temperatures. All as-deposited films have a homogenous amorphous structure, while all annealed films were found to have a two-layered structure composed of a nanocomposite oxidized surface layer of HfO2 particles embedded in a SiOx matrix and an interlayer underneath. As the annealing temperature increased from 1100 ℃ to 1600 ℃, the interlayer structure gradually changes from a homogenous amorphous structure to a nanocomposite structure with nanocrystals embedded in an amorphous matrix. It is also found that a slight change in film composition results a significant change in the microstructure of the interlayer.
This work was supported by the U.S. NSF under Award NSF/CMMI DMREF-1335502.