Microstructure evolution of Incoloy 800H in industrial environment and correlation with creep mechanisms from literature

ABSTRACT

The microstructures of 800 H samples affected by natural corrosion within industrial-like environmental conditions have been studied, and their potential effects on the creep response have been investigated based on literature information. Smooth cylindrical specimens of the alloy extracted from rolled sheet material have been placed into an industrial furnace, where they were exposed to high temperature thermal cycles within an air atmosphere. Samples spending 0 to 5 years inside the furnace underwent a microstructural characterisation campaign. Optical microscopy images reveal no grain coarsening. Macroscopic Vickers hardness shows a relatively wide surface hardness range (115≲HV10≲140). Compared to as-received material, micro-hardness profiles from specimens after years of high-temperature exposure exhibit a surface hardening trend within the vicinity of the edge exposed to the environment. Scanning electron microscopy analyses revealed two coexisting corrosion mechanisms: oxidation and nitridation. The latter is identified as the cause of the micro-indentation hardening trend.

KEYWORDS:

• Austenitic Ni-based alloy
• nitridation
• oxidation
• creep micromechanics
• non-classical creep
• two-step creep minima

Acknowledgments

Carlos Rojas-Ulloa acknowledges the FNRS for funding this research throughout the FRIA grant N° 4000-8987 and FRIA grant N° 4002-1907. The authors acknowledge the funding from the bilateral research cooperation agreement WBI - Wallonie-Bruxelles/AGCID-Chile 2023-2025 RI-02 (DIE23-0001). As research director of F.R.S.-FNRS, A.M. Habraken thanks the Fund for Scientific Research for financial support.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The work was supported by the Agencia Nacional de Investigación y Desarrollo [RI-02 (DIE23-0001)]; Fonds De La Recherche Scientifique – FNRS; Fonds pour la Formation à la Recherche dans l’Industrie et dans l’Agriculture [40021907]; Fonds pour la Formation à la Recherche dans l’Industrie et dans l’Agriculture [40008987 and 400021907]; Wallonie-Bruxelles International [RI-02 (DIE23-0001)].