High-temperature Corrosion of AlCrTiSiN Film in Ar-1%SO 2 Gas
AlCrSiN film with a composition of 29.1Al-17.1Cr-2.1Si-51.7N in at. % was deposited on a steel substrate by cathodic arc ion plating at a thickness of 1.8 μm. It consisted of nanocrystalline hcp-AlN and fcc-CrN, where a small amount of Si was dissolved. Corrosion tests were carried out at 800 ◦C for 5–200 h in Ar-1%SO2 gas. The major corrosion reaction was oxidation owing to the high oxygen affinity of Al and Cr in the film. The formed oxide scale consisted primarily of (Al,Cr)2O3, within which Fe, Si, and S were dissolved. Even after corrosion for 200 h, the thickness of the scale was about 0.7–1.2 μm, indicating that the film had good corrosion resistance in the SO2-containing atmosphere.
Characteristics of (Cr1-x, Alx)N Films Prepared by Pulsed Laser Deposition
Chromium aluminum nitride ((Cr1-x, Alx)N) films have been successfully prepared by pulsed laser deposition (PLD). Experiments were carried out by changing the surface area ratio of the target (Al/(Cr+Al)) from 0 to 100%. From the results of energy-dispersive X-ray spectroscopy (EDS) and Rutherford backscattering spectroscopy (RBS), we have found that the metal content ratio of the film agreed well with the surface area ratio of the target. The hardness of the (Cr1-x, Alx)N films showed the maximum value (HV∼3000) at x=0.75. Phase transition from the B1 (NaCl) structure to the B4 (würtzite) structure occurred above x=0.75, which was in reasonable agreement with the theoretical prediction. The result of the oxidation test revealed that the CrN film was oxidized at approximately 600°C, whereas in the (Cr0.5, Al0.5)N film, the existence of oxide was not detected in the annealing temperature range of RT to 900°C.
High-temperature properties of nanocomposite TiBxNy and TiBxCy coatings
Abstract High-temperature investigations on nanocomposite TiB x N y and TiB x C y 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/TiB 2 or TiC/TiB 2 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 TiB 1.2 N 0.5 and TiB 1.2 C 0.6 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.