Oxide Spallation During Post-isothermal High Temperature Oxidation Cooling of Cr-rich Cast Alloys Highly Alloyed with Hf

Abstract

Cobalt, nickel and iron-based alloys containing 25wt.%Cr and strengthened either by chromium carbides or by HfC were oxidized at 1000, 1100 and 1200°C to obtain external oxide scales. The spallation of these oxides during the post-oxidation cooling was studied by exploiting the cooling part of the thermogravimetry curves. The best resistant alloys against scale spallation were the iron-based alloys which did not lose oxide. The nickel-based alloys well behaved too. The worst alloys were the cobalt alloys, principally due to the complex composition of the oxide scales. Beside the base element, the thickness of the oxide was also identified as a major parameter. The presence of Hf with contents much higher than usual was also beneficial for the resistance against spallation.This is an open access article licensed under the terms of the Creative Commons Attribution-Non-Commercial 4.0 International Public License (CC BY-NC 4.0) (https://creativecommons.org/licenses/by-nc/4.0/legalcode), which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.

Effect of NbC Addition on the High-Temperature Oxidation Resistance of Co- and Ni-Based Chromium-Rich Alloys

“…These observations well meet earlier ones done for more numerous alloys and reported in [18]. In addition, it appeared here that the presence of Nb seemed to be favorable for a better resistance of external oxides against spallation at cooling.…”

Oxide scale spallation behaviour of cast chromia-forming TaC-strengthened superalloys

“…The resulting kinetic competition of outward diffusion of tantalum atoms and the inward diffusion of oxygen allows the oxidation reaction close to the chromia/alloy interface (nickel-based alloys) or deeper and more widely distributed in the carbide-free zone (cobalt-based alloys). This work concerning Ta-rich chromia-forming superalloys based on nickel and cobalt (and even iron) is to add to previous ones in which another type of heavy atom is present (tantalum too [26], or hafnium [27] or molybdenum [28], for instance), and which the oxidation of the heavy element has significant consequences – detrimental or beneficial – on the scale spallation behaviour.…”

Consequences of the additional presence of MC carbides on the behavior in oxidation at 1000°C of a cast Cantor high entropy alloy

“…[ 9–11 ] In contrast with TaC, hafnium carbides do not dissolve and the ones close to the oxidation front are converted into internal oxides and they improve the resistance against oxide spallation in cycling oxidation. [ 12 ] However, their presence in great quantities generally accelerates isothermal oxidation, whatever the base element of the alloy. [ 13–15 ]…”

“…[9][10][11] In contrast with TaC, hafnium carbides do not dissolve and the ones close to the oxidation front are converted into internal oxides and they improve the resistance against oxide spallation in cycling oxidation. [12] However, their presence in great quantities generally accelerates isothermal oxidation, whatever the base element of the alloy. [13][14][15] It is thus important to check whether the behavior of oxidation of such HEA alloys rich in Mn and/or in MCformer metals among Ta and Hf, is compatible with longterm service at high temperatures.…”