Isothermal oxidation of Inconel 625 superalloy at 800 and 1000 degrees C: Microstructure and oxide layer characterization

Author(s)

de Sousa Malafaia, Artur Mariano ^[1] ; de Oliveira, Rafaela Brino ^[2] ; Latu-Romain, Laurence ^[3] ; Wouters, Yves ^[3] ; Baldan, Renato ^[2]

Affiliation

^[1] Sao Joao Rei Fed Univ UFSJ, Campus Santo Anaonio, Praca Frei Orlando 170, BR-36307352 Sao Joao Del Rei, MG - Brazil

^[2] Sao Paulo State Univ UNESP, Campus Itapeva, Rua Geraldo Alckmin 519, BR-18409010 Itapeva, SP - Brazil

^[3] Univ Grenoble Alpes, SIMaP, Grenoble INP, CNRS, F-38000 Grenoble - France

• Document type: Journal article
• Source: MATERIALS CHARACTERIZATION; v. 161, MAR 2020.
• Web of Science Citations: 0

Abstract

Superalloys are widely used in applications at high temperatures and severe environments. Inconel 625 is one of the most applied superalloys due to its high oxidation resistance and mechanical properties, however studies in air lab and temperatures not so extreme as 800 degrees C are still incipient, mainly regarding microstructure characterization and phases formed during aging at high temperatures. The aim of this study was investigating the Inconel 625 isothermal oxidation behavior at 800 and 1000 degrees C for 120 and 240 h in air lab. Thermodynamic simulation was used to guide microstructural characterization performed by SEM/EDS and XRD techniques. Asreceived microstructure presented titanium-niobium (carbo)nitrides and precipitates at grain boundaries. After oxidation, the oxide layer was identified as predominantly chromia in all conditions, providing high oxidation resistance, with some manganese oxidation, suggesting spinel MnCr2O4 formation at 1000 degrees C, besides ABO(4) oxide. Internal alumina oxidation was also observed. Delta phase (Nb,Mo)Ni-3 was noticed at graM boundaries (800 degrees C) and at metal/oxide interface for both temperatures as result of chromium depletion. Some spallation zones were observed at 1000 degrees C, but this fact did not decrease the good oxidation resistance, as observed at 800 degrees C. Finally, photoelectrochemistry (PEC) result demonstrated a p-type semiconductor character for chromia scale after 120 h at 800 degrees C, that was associated to the porous oxide layer and delta phase formation. (AU)

• FAPESP's process: 18/07802-9 - Microstructural characterization, isothermal and cyclic oxidation resistance at high temperatures of conventional and Nb-modified MAR-M246 superalloys
• Grantee: Renato Baldan
• Support Opportunities: Regular Research Grants
• FAPESP's process: 17/06515-3 - Microstructural characterization and oxidation tests of inconel 625 nickel-based superalloy
• Grantee: Rafaela Brino de Oliveira
• Support Opportunities: Scholarships in Brazil - Scientific Initiation