Influence of copper and aluminum substitution on high-temperature oxidation of the FeCoCrNiMn “Cantor” alloy

In this study, the oxidation behavior of FeCoCrNiMn (HEA + Mn) is compared to three modified HEAs manufactured by substituting Mn with Al, Cu, or Al + Cu. Oxidation tests were conducted between 600°C and 800°C for up to 500 h in synthetic air. Substitution of Mn leads to a significant improvement in the oxidation resistance for the three modified HEAs. For FeCoCrNiCu (HEA + Cu), a local attack of a Cu-rich phase was observed, leading to the formation of CuO blisters on the surface. The FeCoCrNiAl (HEA + Al) alloy was characterized by the formation of a thin Al2O3 surface layer for all temperatures. However, for the HEA + Al alloy the formation of AlN was observed after 300 h at 800°C, leading to a partial breakdown of the protective scale. FeCoCrNiCuAl (HEA + Cu + Al) by far showed the best oxidation resistance, characterized by the formation of a highly protective Al2O3 scale that effectively inhibited nitrogen penetration into the metal subsurface and local attack of the Cu-rich phase.This article is published as Bürckner, Mary‐Lee, Lukas Mengis, Emma MH White, and Mathias C. Galetz. "Influence of copper and aluminum substitution on high‐temperature oxidation of the FeCoCrNiMn “Cantor” alloy." Materials and Corrosion 74, no. 1 (2023): 79-90. DOI: 10.1002/maco.202213382. Copyright 2022 DECHEMA. Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0). Posted with permission. DOE Contract Number(s): AC02-07CH11358

Effects of tungsten alloying and the fluorination on the oxidation behavior of intermetallic titanium aluminides for aerospace applications

International audienceCurrent limitations to a wider use of intermetallic TiAl alloys in aircraft and automotive en-gines arise from an insufficient oxidation resistance at temperatures above approximately 800°C. In this paper, the high temperature oxidation behavior of three engineering -TiAl-based alloys at 900°C in air is reported. The performance of the TNM alloy (Ti-43.5Al-4Nb-1Mo-0.1B), the 4822 alloy (Ti-48Al-2Cr-2Nb), and the Nb-free IRIS alloy (Ti-48Al-2W-0.08B) is compared (all chemical compositions are given in at.%). During testing in air non-protective mixed oxide scales developed on all untreated samples, but with different compositions and thicknesses. These different oxide layers are characterized and their formation mechanisms are discussed. The presence of W in the IRIS alloy leads to a better oxidation behavior compared to untreated TNM and 4822. This behavior was changed in the direction of a protective alumina layer formation via the so-called “fluorine effect”. The above-mentioned alloys were treated with fluorine via a liquid phase process by evenly spraying a fluorine containing polymer on all faces of the specimens. The oxidation resistance of the fluorine treated samples was signifi-cantly improved compared to the untreated specimens. Due to the fluorination all treated test coupons exhibited slow oxidation kinetics. The results of isothermal as well as thermocyclic exposure tests are presented and discussed in the view of the chemical composition and pro-cessing conditioned microstructure of the three investigated γ-TiAl-based alloys

Investigations of the Deuterium Permeability of As-Deposited and Oxidized Ti2AlN Coatings

Aluminum containing Mn+1AXn (MAX) phase materials have attracted increasing attention due to their corrosion resistance, a pronounced self-healing effect and promising diffusion barrier properties for hydrogen. We synthesized Ti2AlN coatings on ferritic steel substrates by physical vapor deposition of alternating Ti- and AlN-layers followed by thermal annealing. The microstructure developed a {0001}-texture with platelet-like shaped grains. To investigate the oxidation behavior, the samples were exposed to a temperature of 700 °C in a muffle furnace. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) depth profiles revealed the formation of oxide scales, which consisted mainly of dense and stable α-Al2O3. The oxide layer thickness increased with a time dependency of ~t1/4. Electron probe micro analysis (EPMA) scans revealed a diffusion of Al from the coating into the substrate. Steel membranes with as-deposited Ti2AlN and partially oxidized Ti2AlN coatings were used for permeation tests. The permeation of deuterium from the gas phase was measured in an ultra-high vacuum (UHV) permeation cell by mass spectrometry at temperatures of 30–400 °C. We obtained a permeation reduction factor (PRF) of 45 for a pure Ti2AlN coating and a PRF of ~3700 for the oxidized sample. Thus, protective coatings, which prevent hydrogen-induced corrosion, can be achieved by the proper design of Ti2AlN coatings with suitable oxide scale thicknesses