Potential of the Halogen Effect for the Formation of a Protective Alumina Scale on Ni‐Base Superalloys

Abstract

The application of the halogen effect was extended to Ni-base superalloys with low aluminium content. A dense protective alumina scale can be formed by increasing the Al-activity through the halogen effect. Thermodynamic calculations predicted the existence of a region for the F-and Cl-effect for the alloys IN738 and IN939 at temperatures between 900°C and 1200°C. The suitable F-and Cl-concentrations were found for IN738 by using ion implantation. The oxidation mechanism changed from an inward-growing discontinuous scale to a dense continuous protective alumina layer. The F-effect on IN738 improves the oxidation resistance during long term oxidation. By using the Feffect a pure alumina scale was also obtained for alloy CMSX-4.

Protective Alumina Scale Growth at 900 °C for a Ni- and Cr-Free Co-Base Model Alloy with γ/γ’-Microstructure: Synergistic Effects by Combining Shot-Peening and Halogenation

“…Correspondingly, this approach is typically referred to as the halogen effect. In principle, the halogen effect can be caused by various halogens; however, most promising results were obtained for fluorine [24,25]. For applying the latter, typically, ion implantation is conducted, even though also other methods such as liquid phase immersion with diluted HF-based solutions are suitable [26,27].…”

“…Thereby, both alumina and gaseous fluorine are yielded. The latter is extremely reactive and can subsequently return to the cycle [25].…”