High-temperature properties of nanocomposite TiBxNy and TiBxCy coatings

High-temperature investigations on nanocomposite TiBxNy and TiBxCy coatings were performed to determine their thermal stability. All coatings investigated were prepared by means of unbalanced DC magnetron co-sputtering using either a segmented TiN/TiB2 or TiC/TiB2 target. Recovery and recrystallization behavior were characterized by means of stress measurements during thermal annealing and differential scanning calorimetry (DSC). The nanocomposite coatings used for DSC measurements were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD of these coatings showed a pronounced growth of the individual phases after the DSC measurements. Therefore, the total enthalpy change during DSC can be attributed to grain growth of the nanocrystalline phases. The grain sizes after the DSC treatment as analyzed by XRD and SEM are in excellent agreement with the grain sizes calculated from the exothermic peaks of the DSC measurements. Grain growth occurred for the individual phases in TiB1.2N0.5 and TiB1.2C0.6 coatings during heating up to 1400°C from approximately 4 to 15 nm and 4 to 5 nm, respectively. Recovery effects of the coatings investigated are strongly influenced by the ion bombardment during film growth as well as by the chemical composition of the coatings.