HEA 2023: Oxidation and Corrosion of HEAs I
Program Organizers: Andrew Detor, DARPA/DSO; Amy Clarke, Los Alamos National Laboratory
Monday 9:00 AM
November 13, 2023
Room: Riverboat
Location: Omni William Penn
Session Chair: John Scully, University of Virginia
9:00 AM Introductory Comments
9:05 AM Invited
Nb2TiO7 as a Protective Oxide for Refractory Alloys: Elizabeth Opila1; Charlie Brandenburg1; Brandol Galicia1; Hailey Boyd1; Mitra Taheri2; 1University of Virginia; 2Johns Hopkins University
Oxidation of NbTiZr refractory alloys are being studied as a model for refractory multiple principal element alloys (RMPEA). Oxidation of equimolar NbTiZr at temperatures between 900 and 1200C resulted in the formation of TiO2 and Nb2TiO7 surface oxides. In the 1960s, alloy B-1 (Nb-15Ti-10Ta-10W-3Al-2Hf, in wt%) was identified as a relatively oxidation resistant Nb-base alloy and it was hypothesized that the formation of Nb2TiO7 offered some protection. In this study oxidation kinetics of equimolar NbTiZr, C-103, and alloy B-1 are compared under the same conditions. In addition, the complex oxide Nb2TiO7 was synthesized from constituent oxides by spark plasma sintering to characterize properties important for protective thermally grown oxides including melting temperature and thermal expansion coefficient. The goal of this work is to contribute to our understanding of Nb- and Ti-containing RMPEA oxidation mechanisms.
9:35 AM
Electrochemical Technique to Characterize the High Temperature Oxidation Behavior of Materials: Koen Verrijt1; David Poerschke1; 1University of Minnesota Twin Cities
Oxidation limits the lifetime of many materials in high temperature applications. Developing more durable materials requires detailed understanding of the oxidation reactions and rates. Some commonly used analytical techniques, such as thermogravimetric analysis, measure the net mass change of the specimen over time. Other techniques, such as cross-sectional analysis of oxidized specimens, provide insight into the oxide scale microstructure. However, the information obtained with these techniques is insufficient to understand complex oxidation phenomena. This work presents an analytical technique that utilizes solid-state electrochemical oxygen pumps to control the oxidation potential and measure the resulting oxygen consumption of a material. This approach, which provides specific advantages when studying multi-principal element alloys (MPEA) that form a mixture of condensed and gaseous oxides, was applied to study the effect of aluminum on the oxidation resistance of refractory MPEAs and better account for reactions resulting in simultaneous mass gain and loss for molybdenum-containing specimens.
9:55 AM
Oxidation Behaviors of Ta-Ti-Cr RMPEAs: Noah Welch1; Todd Butler2; Maria Quintana1; Samuel Kuhr2; Peter Collins1; 1Iowa State University; 2Air Force Research Laboratory, WPAFB
Refractory Multi-Principal Element Alloys (RMPEAs) have been shown to exhibit favorable oxidation resistance at high temperatures (>1000°C) due to the formation of complex oxides and suppression of simple, deleterious oxides such as Ta2O5. The TaTiCr alloy family shows promise in this space with relatively low density, high melting temperature and enhanced oxidation resistance when compared to traditional, dilute refractory alloys. An in-depth characterization of the role of microstructure, alloy chemistry and temperature on the resulting oxidation behaviors will be discussed. The resulting oxides, kinetics and associated thermodynamics will be addressed with respect to related alloys systems. Future challenges with respect to the understanding of RMPEA oxidation will also be described.
10:15 AM
Tuning Scale Formation in Al-containing Refractory High Entropy Alloys via Reactive Elements Addition: Elaf Anber1; David Beaudry1; Charlie Brandenburg2; Sebastian Lech1; Michael Waters3; Nathan Smith3; James Rondinelli3; Chris Wolverton3; Elizabeth Opila2; Jean Phillippe Couzinie4; Mitra Taheri1; 1Johns Hopkins University; 2University of Virginia; 3Northwestern University; 4University Paris-Est Créteil (UPEC) - IUT
Refractory high entropy alloys (RHEAs) hold the promise of superior mechanical properties at high temperatures, however, their oxidation resistance is still a major drawback because of the formation of non-protective scales. The classical concept (i.e. addition of Cr/Al) of providing oxidation resistance to high temperature alloys has been unsuccessful due to the inability to form a continuous scale. Using a combination of multiscale microscopy and thermodynamic calculations, we examined the role of Al and reactive elements (REs) addition on scale formation in RHEAs, and the alloys tend to passivate, forming continuous Al2O3, with decreasing REs/Al additions. We also observed the formation of complex oxides such as Nb2O5 and Nb2Zr6O17 with increasing Al/REs concentration. The structure, composition and density of these oxides will be discussed in terms of concentration of oxygen/metal vacancy. These results provide a one step closer towards designing new RHEAs that are better suited for high temperature environments.
10:35 AM Break
10:55 AM
High Temperature Oxidation Mechanisms of NbTiZr Using 18O Tracer Technique: Charlie Brandenburg1; David Beaudry2; Mitra Taheri2; Elizabeth Opila1; 1University of Virginia; 2Johns Hopkins University
Refractory multi-principal element alloys (RMPEAs) are of interest for their mechanical strength at high temperature, however, rapid oxidation rates limit their use in these environments. Equimolar NbTiZr was studied as a model alloy for high temperature oxidation of RMPEAs. Double oxidation experiments using 1%O2 (balance argon) and 18O2 tracer gas were performed at 1050°C and 1250°C using a resistive heating system. Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) was used to map the distribution of 18O in sample cross-sections. 18O exposure for 1 minute and 30 seconds after oxidation at 1050 and 1250°C, respectively, resulted in an 18O reaction depth of approximately 40μm. ToF-SIMS maps of the sample oxidized at 1250°C show high concentrations of 18O in ZrO2 grains, suggesting rapid transport of oxygen within ZrO2.
11:15 AM
Multi-scale Characterization of Al0.3CrFeNiTi0.3 High-entropy Alloy Coatings Produced by High-velocity Oxygen-fuel (HVOF) Spraying: Rasim Eris1; Ashok Meghwal2; Surinder Singh2; Christopher C. Berndt2; Andrew Siao Ming Ang2; Paul Munroe1; 1UNSW Sydney; 2Swinburne University of Technology
Incorporating lighter elements, such as Al and Ti, into AlxCrFeNiTiy high-entropy alloys (HEAs) produced by bulk processing methods significantly enhances both strength and ductility, compared to many CrFeNi-based HEAs. Nevertheless, high entropy alloy coatings (HEACs) allow these alloys to be exploited as protective films. In this current work, a high-performance Al0.3CrFeNiTi0.3 HEAC was produced by the high-velocity oxygen-fuel (HVOF) thermal spraying technique and characterized by scanning and transmission electron microscopy. Micro-hardness and nano-indentation tests were used to establish a correlation between specific microstructural features and local mechanical properties. Accordingly, strengthening was seen to be enhanced by the presence of dispersed oxides formed by in-flight oxidation “IFO” during deposition. Moreover, this coating exhibits a highly complex multiphase microstructure including ordered structures with distinctive grain morphologies and local chemical heterogeneities that contributed to the attractive mechanical properties.
11:35 AM
Effect of Surface Deformation on the High-temperature Oxidation Response of Equimolar CrMnFeCoNi: Thomas Valenza1; Kate Moo1; Emmanuelle Marquis1; 1University of Michigan
Because of its role in the high-temperature oxidation of many alloys, surface deformation has the potential to influence the oxidation response of HEAs. To demonstrate its importance for HEAs, we compared the oxidation response of an equimolar CrMnFeCoNi alloy subjected to different surface finishes. Specimens were either polished to a mirror finish, to minimize surface deformation, or ground with coarse SiC paper, to maximize surface deformation. Prepared specimens were oxidized in air at 800 °C, and the resulting oxide scales and sub-surface microstructures were characterized. The oxidation response differed dramatically as a function of the surface finish. Differences were noted in the oxide scale thicknesses, oxidation products, and internal oxidation. Furthermore, diffusion-induced grain-boundary migration appears to play a key role in the oxidation process of deformed surfaces. The present results point to possible variations in the oxidation response of commercial components due to varying processing conditions and surface finish.
11:55 AM
A High Throughput CALPHAD Method of Designing Low Density, Compositionally-complex Alloys Toward Understanding Lightweighting Elements' Effects on Passivity: Peter Connors1; John Scully1; 1University of Virginia
The emergence of compositionally-complex alloys (CCAs) as a new frontier of corrosion-resistant alloys has opened doors for advanced optimization of the usage of corrosion-resistant elements for promoting passivation of each phase and self-healing. However, researchers must contend with a design space unfathomable in compositional and microstructural possibilities. In this work, a methodology for the rapid (~1 alloy/second) testing of alloy compositions for desired phase stability using the CALPHAD approach is presented. This approach utilizes equilibrium information of a composition at its solidus temperature to maximize the probability of discovering an alloy with a disordered matrix-(or single-)phase microstructure. Additionally, for multi-phase alloy design, this approach engineers the distribution of passivating elements throughout the predicted microstructure and interfacial area between phases of interest. Alloys with constant phase compositions and variable area fractions are evaluated. A system discovered using this technique is explored toward understanding lightweight, passivating elements’ effects on overall passivation.