ABSTRACT
Picosecond-pulsed ultraviolet-laser (UV-355 nm) assisted atom probe tomography (APT) was used to analyze protective, thermally grown chromium oxides formed on stainless steel. The influence of analysis parameters on the thermal tail observed in the mass spectra and the chemical composition is investigated. A new parameter termed "laser sensitivity factor" is introduced in order to quantify the effect of laser energy on the extent of the thermal tail. This parameter is used to compare the effect of increasing laser energy on thermal tails in chromia and chromite samples. Also explored is the effect of increasing laser energy on the measured oxygen content and the effect of specimen base temperature and laser pulse frequency on the mass spectrum. Finally, we report a preliminary analysis of molecular ion dissociations in chromia.
ABSTRACT
Multilayered AlTiSiN films with a composition of 32.0Al-12.4Ti-4.9Si-50.7N (at.%) were deposited on a steel substrate in a nitrogen atmosphere by cathodic arc plasma deposition. The films consisted of crystalline approximately 8 nm-thick AISiN nanolayers that originated from the Al-Si target and approximately 3 nm-thick TiN nanolayers that originated from the Ti target. Their oxidation characteristics were studied between 600 and 1000 degrees C for up to 20 h in air. They displayed good oxidation resistance due to the formation of a thin, dense Al2O3 surface scale below which an (Al2O3, TiO2, SiO2)-intermixed inner scale existed. They oxidized slower than TiN films because protective Al2O3-rich scales formed on the surface. However, they oxidized faster than CrN films because impure Al2O3 scale formed on the AlTiSiN film. Their oxidation progressed primarily by the outward diffusion of nitrogen and substrate elements, combined with the inward transport of oxygen that gradually reacted with Al, Ti, and Si in the film.
ABSTRACT
High-purity, dense nano-laminated (Cr0.95Ti0.05)2AlC compounds were synthesized via a powder metallurgical route. Their oxidation characteristics were investigated by exposing them to temperatures between 900 and 1200 degrees C in air. The alloying Ti in the Cr layer of Cr2AlC did not significantly change the crystal structure and microstructure of Cr2AlC. But, it increased the oxidation rate of the Cr,AlC. The scale morphology of the (Cr0.95Ti0.05)2AlC was basically similar to that of the pure Cr2AlC. The main difference was that the (Cr0.95Ti0.05)2AlC contained oxide nodules. These formed because the titanium oxidized to TiO2, making the Cr2AlC susceptible to nodular oxidation. However, alpha-Al2O3 was still the major oxidation product in both the (Cr0.95Ti0.05)2AlC and pure Cr2AlC.
