TY - THES

T1 - Thermal stability and oxidation behavior of sputtered CrAl(Y) intermetallic coatings

AU - Kranjcec-Strahl, Ivan

N1 - embargoed until null

PY - 2010

Y1 - 2010

N2 - The objective of this work is to show the possibilities of coatings and coating technologies for use in high-temperature industrial applications. Chromium-aluminum coatings, with a fixed atomic percent ratio of 40 to 60 and a variable yttrium content of 0, 2 and 4 at% have been studied. The coatings were prepared by unbalanced magnetron sputtering of CrAl(Y) targets using an Ar glow discharge. The substrates were titanium aluminides, a nickel base alloy and sapphire. Annealing experiments of these coated materials were performed in vacuum at 900°C for up to 1h and oxidation experiments were conducted in ambient atmosphere also at 900 °C for up to 50h. Examinations of the annealed as well as oxidized coated materials were conducted using x-ray diffraction, scanning electron and optical microscopy. The coatings have undergone significant microstructural and chemical changes due to diffusion and oxidation. It was shown that the coatings provide oxidation protection for the base material to a certain extent. An addition of 2 at% Yttrium to the Cr0.6Al0.4 coating shows an increased oxidation resistance when using inert substrates like sapphire but an increasing mass gain for coatings on Ni base super alloys as well as on TiAl alloys. Nevertheless, the addition of 2at% Y to the Cr-Al coatings promote the formation of the stable alpha-prime Al2O3. Higher Yttrium contents are detremental for the oxidation protection. Energy dispersive spectrometry line scans on polished cross sections exhibit a significant diffusion of nitrogen (from the ambient atmosphere) through the CrA(Y) coating into the bulk material, followed by formation of nitrides within the top most 5 µm of the bulk material, especially when using a titanium aluminide alloy.

AB - The objective of this work is to show the possibilities of coatings and coating technologies for use in high-temperature industrial applications. Chromium-aluminum coatings, with a fixed atomic percent ratio of 40 to 60 and a variable yttrium content of 0, 2 and 4 at% have been studied. The coatings were prepared by unbalanced magnetron sputtering of CrAl(Y) targets using an Ar glow discharge. The substrates were titanium aluminides, a nickel base alloy and sapphire. Annealing experiments of these coated materials were performed in vacuum at 900°C for up to 1h and oxidation experiments were conducted in ambient atmosphere also at 900 °C for up to 50h. Examinations of the annealed as well as oxidized coated materials were conducted using x-ray diffraction, scanning electron and optical microscopy. The coatings have undergone significant microstructural and chemical changes due to diffusion and oxidation. It was shown that the coatings provide oxidation protection for the base material to a certain extent. An addition of 2 at% Yttrium to the Cr0.6Al0.4 coating shows an increased oxidation resistance when using inert substrates like sapphire but an increasing mass gain for coatings on Ni base super alloys as well as on TiAl alloys. Nevertheless, the addition of 2at% Y to the Cr-Al coatings promote the formation of the stable alpha-prime Al2O3. Higher Yttrium contents are detremental for the oxidation protection. Energy dispersive spectrometry line scans on polished cross sections exhibit a significant diffusion of nitrogen (from the ambient atmosphere) through the CrA(Y) coating into the bulk material, followed by formation of nitrides within the top most 5 µm of the bulk material, especially when using a titanium aluminide alloy.

KW - CrAlY

KW - PVD

KW - Oxidation

KW - TiAl

KW - Nimonic80A

KW - CrAlY

KW - PVD

KW - oxidation

KW - TiAl

KW - Nimonic80A

M3 - Diploma Thesis

ER -