Environmental Degradation of Multiple Principal Component Materials: High Temperature Corrosion I
Sponsored by: TMS Structural Materials Division, TMS: Corrosion and Environmental Effects Committee
Program Organizers: Wenjun Cai, Virginia Polytechnic Institute and State University; XiaoXiang Yu, Novelis Inc.; Vilupanur Ravi, California State Polytechnic University Pomona; Christopher Weinberger, Colorado State University; Elizabeth Opila, University of Virginia; Bai Cui, University of Nebraska Lincoln; Mark Weaver, University of Alabama; Bronislava Gorr, Karlsruhe Institute of Technology (KIT); Gerald Frankel, Ohio State University; ShinYoung Kang, Lawrence Livermore National Laboratory; Srujan Rokkam, Advanced Cooling Technologies, Inc.

Monday 8:30 AM
March 20, 2023
Room: Sapphire 410A
Location: Hilton

Session Chair: Bronislava Gorr, Karlsruhe Institut für Technologie; Mark Weaver, The University of Alabama


8:30 AM  Invited
Conditions for Exclusive External Scale Formation in the High Temperature Oxidation of Alloys: Karl Sieradzki1; William Blades1; Elizabeth Opilia2; 1Arizona State University; 2University of Virginia
     Within the context of Wagner’s oxidation theory, the conditions for exclusive external scale formation are examined using a recursive-sequence approach which has a fixed-point defining the critical mole fraction of the passivating component in a binary single-crystal alloy. These results highlight the importance of lateral growth of oxide particles. Next, a thin-film growth analogy for a kinetic model of exclusive external scale growth is described. This model is presumed to be operative during transient oxidation. The unknown parameters required to test the usefulness of this approach includes the surface/interfacial diffusivities of oxygen species as well as that of the scale forming component and the magnitude of Ehrlich-Schwoebel barriers. Even lacking these results, the analysis shows that for a large enough nucleation density of oxide particles, exclusive external oxide scales should form. Work supported by the Office of Naval Research, under Grant Number N00014-20-1-2368

8:50 AM  
Effect of the Chemical Composition on the Formation of Compact (Cr,Ta,Ti)O2 Scales on Refractory High-entropy Alloys (RHEAs) within the Ta-Mo-Cr-Ti-Al System: Steven Schellert1; Hans-Jürgen Christ1; Stephan Laube2; Alexander Kauffmann2; Martin Heilmaier2; Bronislava Gorr3; 1Universität Siegen; 2Karlsruher Institut für Technologie (KIT IAM-WK); 3Karlsruher Institut für Technologie (KIT IAM-AWP)
    RHEAs are potential candidates for high temperature applications. The superior oxidation resistance of the equiatomic TaMoCrTiAl relies on the formation of a (Cr,Ta,Ti)O2 scale. In this contribution, various alloys within the Ta-Mo-Cr-Ti-Al system with different Ta, Cr, Al and Ti contents as well as a Mo-free alloy are investigated to understand the influence of the chemical composition on the formation of Cr,Ta,Ti)O2. It was found that the elements Cr and Ta are indispensable to form a compact (Cr,Ta,Ti)O2 layer. At least 15 at.% Cr and Ta are required to guarantee the (Cr,Ta,Ti)O2 formation, at lower concentrations mixed oxides are formed. It is assumed that Al concentrations higher 15 at.% support the (Cr,Ta,Ti)O2 formation owing to getter and nucleation effects. The removal of Mo causes enhanced internal oxidation due to the unfavorable changes in the microstructure. Ti exhibits a positive effect by reducing the concentration of oxygen vacancies in the oxide.

9:10 AM  
Flow and Steam Enhanced Degradation of Once Through Steam Generation Piping Steels: Kevin Hodder1; Omnath Ekambaram1; Saeid Dehghani1; John Nychka1; Basil Perdicakis2; R. Sean Sanders1; 1University of Alberta; 2Suncor Energy
    Once through steam generation (OTSG) piping operates under severe environmental conditions including high temperature, aqueous fluids with chemical additives (which may act as corrosive impurities), and high flow rates. The ability of piping steels in OTSGs to withstand such environmental conditions depends heavily on the combination, and synergistic effects, of the environmental conditions and the underlying chemistry and metallurgical structure of the steels of choice. This work describes various degradation mechanisms acting on industry supplied cutouts of piping from in service OTSGs, and results from a custom designed batch autoclave designed to recreate OTSGs conditions on a lab bench scale. Visual examination and materials characterization techniques (e.g., optical and electron microscopy with EDX, x-ray diffractometry, metallurgical microstructural analysis) were employed to elucidate the degradation mechanisms acting in various operating envelopes. Observed damage modes responsible for severe metal losses ranged from crevice corrosion, pitting corrosion, flow enhanced corrosion, and caustic attack.

9:30 AM  
High Temperature Oxidation of CoNiFeMnCr High Entropy Alloys Reinforced by MC-carbides: Patrice Berthod1; 1University of Lorraine
     CoNiFeMnCr alloys are possibly alternative solutions to cast cobalt or nickel superalloys able for service at 1000°C and beyond. The partial substitution of Co and Ni by Fe and Mn allow lower dependence on the Co and Ni critical elements. In this work, equimolar CoNiFeMnCr alloys without or with added carbon and tantalum or hafnium were elaborated by high frequency induction melting under inert atmosphere. Script-like eutectic TaC or HfC were obtained in the grain boundaries of the concerned alloys, forming a strengthening carbides network. Oxidation tests were carried out in air at 1000°C and at 1100°C for 50h hours. The oxide scale externally formed is made of (Cr,Mn)2O3. Internal oxidation led to CrTaO4 or HfO2 oxides. Numerous deep oxidation penetrations were noted for the CoNiFeMnCr alloy while the MC-containing alloys were not affected by this phenomenon, evidencing a possible beneficial influence of the presence of the carbides on oxidation.

9:50 AM Break

10:05 AM  
Investigation of Spinel Phase Formation on Ni-doped FeCrAl Alloy in Multiple Environments: Rajnikant Umretiya1; Andrew Hoffman1; Richard Blair1; Robert Motly1; Timothy Jurewicz1; Raul Rebak1; 1GE Research
    FeCrAl alloys are considered as lead Accident Tolerant Fuel (ATF) candidate because of their ability to form a passive Al film during high temperature exposure above ~800C. Additionally, FeCrAl alloys are highly corrosion resistant in hydrothermal exposures due to the formation of a protective oxide film which is two-layer structure, consist of outer oxide layer with porous Fe3O4 and inner oxide layers with compact polycrystalline FeCr2O4. The oxygen (O) can diffuse through this spinel layers to form Cr2O3 on the bulk surface, which protects the bulk from further oxygen diffusion and oxidation. Recently, it was found that in the irradiative environment, Fe-based spinel is not stable; however, NiFe2O4 is stable due to the stability of which over a large ECP and pH range in the E-pH (pourbaix) diagram. Thus, this study explores the formation/stability of NiFe2O4 spinel in Ni added FeCrAl alloys after exposure in different non-irradiated corrosion environments.

10:25 AM  Invited
Elemental Effects on Oxidation Kinetics of Refractory High Entropy Alloys: Hideyuki Murakami1; Moreau Louis1; Wei-Chih Lin2; Kai-chi Lo2; Stephane Gorsse3; An-chou Yeh2; 1National Insititute for Materials Science; 2National Tsing Hua University; 3CNRS, Univ. Bordeaux
    There is a continuous requirement to develop materials with higher temperature capabilities, because employment of these materials to internal combustion engines could enable us to operate internal combustion engines at higher temperatures, which results in the reduction of CO2 generation. Refractory high entropy alloys (RHEAs) or refractory compositionally complex alloys (RCCAs) are candidates of the next generation high temperature structural materials due to their high melting temperatures and reasonably good mechanical properties. On the other hand, such materials should have protective properties against oxidation and hot corrosion, thereby their oxidation behabior should be systematically investigated. This study focuses on the RHEAs or RCCAs which consist of the combination of following elements : Nb, Ti, Ta, Cr, Mo, Al. The effects of alloy composition on their mass change kinetics, constitution of thermally grown oxides will be systematically investigated and discussed.

10:45 AM  
Role of Surface Deformation on the High-Temperature Oxidation Response of FeNiCr-based HEAs: Kate Moo1; Daniele Fatto Offidani1; Emmanuelle Marquis1; 1University of Michigan
    High-entropy alloys (HEAs) have gained interest in recent years due to their unique properties. However, the high-temperature oxidation behavior of HEAs remains not well understood, albeit its industrial relevance. Surface deformation has been found to impact the oxidation kinetics and oxide growth mechanisms in conventional alloys, but these effects pertaining to HEAs are notably absent in the literature. This study aims to shed light on the impact of surface deformation on the high-T oxidation behavior of two equimolar quinary HEAs, along with the main drivers behind the formation of the oxide(s). Samples of ground and alumina-polished equimolar FeNiCrCoMn and FeNiCrCoAl were oxidized at temperatures ranging from 500-800C. Differences in oxide thickness, composition, and structure, along with bulk microstructural properties, will be discussed, shedding light on the evolution of the oxide with time and its underlying kinetic contributors from the bulk metal and grain boundaries.