Study of the mechanisms of initial oxidation and of the interaction with reactive elements in the halogen effect for Ni-base alloys
Final Report Abstract
Ni-based superalloys with relatively low Al-contents between 3-5 at.% are often used in high temperature technology. Due to their low amount of Al these alloys are unable to form a protective alumina scale. The halogen effect – working successfully for Gamma-TiAl-alloys – offers a new way to form a protective alumina scale also for these Ni-base alloys. For the surface modification F-ion implantation was applied performing a screening to find the suitable “window” for the halogen (fluorine) effect. For alloy IN 738 a change of oxidation mechanism was achieved to form an outward growing dense protective alumina scale during oxidation at 1050°C. Also for alloy Haynes 214 the tendency to form a protective alumina scale can be supported by surface modification via fluorine ion implantation. The formed alumina scale shows a more protective structure due to a lack of inclusions like chromia. In case of alloy PWA 1484 no significant influence on scale formation was found. This alloy already forms a thin alumina scale at the metal/oxide-interface. Due to the low Al content in alloy RR1000 no protective alumina scale was found. A successful application of the halogen effect would become possible, if the surface region will be enriched with Al by e. g .CVD processes before doping the surface with fluorine. The halogen effect was combined with the reactive element (RE) effect to improve the adherence of the thin protective alumina scale. The subsequent ion implantation with F and the RE Y and Hf showed how important the implantation sequence is. At first the RE must be implanted, followed by fluorine. As optimal implantation parameters were determined: 1. Implantation with Hf: (2 .. 4) x 10^16 Hf cm^-2 2. Implantation with F: (0.5 .. 1) x 1017 F cm^-2 2. Implantation with Y: 4 x 1016 Y cm^-2 2. Implantation with F: (0.5 .. 1) x 1017 F cm^-2 Those alloys containing small amounts of reactive elements reveal a suitable adherece of the alumina scale. No surface modification with RE is needed.
Publications
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Volume 5. Glossa:
Zschau, H.-E.; Schütze, M.; Galetz, M. C.; Gleeson, B. M.; Neve, S.; Lorenz, M.; Grundmann, M.
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Implantation of Y- and Hf-Ions into a F-doped Ni-Base Superalloy Improving the Oxidation Resistance at High Temperatures. Nuclear Inst. and Methods in Physics Research, B 365 (2015) 202-206
H.-E. Zschau, F. King, M.C. Galetz, M. Schütze
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Promotion of the Al2O3-Scale Formation on Ni-Cr-Al Alloys via the Fluorine Effect. Oxidation of Metals, vol. 83 (2015), issue 3-4, 335-349
H.-E. Zschau, W. Zhao, S. Neve, B. Gleeson, M. Schütze
