High Entropy Alloys IX: Structures and Modeling
: Structures and Characterization IV
Sponsored by: TMS Functional Materials Division, TMS Structural Materials Division, TMS: Alloy Phases Committee, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Peter Liaw, University of Tennessee; Michael Gao, National Energy Technology Laboratory; E-Wen Huang, National Chiao Tung University; Srivatsan Tirumalai; Xie Xie, FCA US LLC; Gongyao Wang, Globus Medical
Thursday 2:00 PM
March 18, 2021
Room: RM 9
Location: TMS2021 Virtual
Session Chair: Eun Park, Seoul National Univerisity; Stefano Curtarolo, Duke University
2:00 PM Invited
Rational Use of Entropy Unavoidability in High-entropy Ceramics: Stefano Curtarolo1; 1Duke University
In this presentation we will discuss methods and directions to self-stabilize disorder in high-entropy ceramics, and its contribution in thermodynamic properties. Research sponsored by DOD.
2:20 PM
Examination of the Bulk Metal-oxide Layer Interface of a Cr-Nb-Ta-V-W High Entropy Alloy at 700 and 800oC: Rebecca Romero1; S.K. Varma1; Nanthakishore Makeswaran1; Ravisankar Naraparaju1; C.V. Ramana1; 1The University of Texas at El Paso
The bulk metal-oxide layer interface of a Cr-Nb-Ta-V-W high entropy alloy was exposed to temperatures of 700 and 800oC in air and examined in the oxidized state. An untreated sample was also subjected to high temperature x-ray diffraction measurements to determine oxide patterns up to 800oC. Five different phases which were previously identified in this alloy was confirmed. The microstructure near the interface was studied for an indication of selective oxidation of this alloy. Oxidized samples at 700 and 800oC were studied to evaluate the differences in oxide composition and morphology at interface and surface layer. SEM was employed to evaluate the physical structure of the interface and oxide surface layer, while EDS and x-ray color mapping was utilized to characterize the elemental composition of the bulk metal and oxide layers.
2:40 PM
Ex-situ and In-situ Characterization of Early Stage Oxidation Mechanism of High Entropy Alloys: Bharat Gwalani1; Sten Lambeets1; Matthew Olszta1; Daniel Perea1; Arun Devaraj1; 1Pacific Northwest National Laboratory
High Entropy Alloys (HEAs) show promise for use in high temperature applications in which they are exposed to reactive environments containing oxygen gas (O2). Oxidation reactions directly modify the surface composition-structure, affecting the material performance. However, due to the complex HEA composition, atomistic mechanisms responsible for surface modification are inadequately understood. Here, we demonstrate the oxidation-induced change in structure of near-surface regions using correlative transmission electron microscopy and atom probe tomography. Additionally, we report the application of an environmental reaction chamber attached to an atom probe tomography system, used to expose the same HEA alloy to oxidation conditions, to capture oxide formation in situ. This latter approach is aiding a detailed understanding of the sequential oxidation of specific alloying elements in HEAs and is broadly applicable to a wide variety of other complex alloy material systems.
3:00 PM
On Sluggish Diffusion in Random, Equimolar FCC Alloys: Murray Daw1; Michael Chandross2; 1Clemson University; 2Sandia National Laboratories
We investigate the claims (see, for example, W. Yeh, et al., Adv. Eng. Mater., 2004) that increasing the number of constituents in compositionally complex random alloys causes diffusion to be sluggish. Our theoretical calculations of vacancy-assissisted diffusion in the 57 random, equimolar alloys that can be formed from Cu, Ag, Au, Ni, Pd, and Pt are based on the well-tested Embedded Atom Method functions of Foiles, Baskes, & Daw (S.M. Foiles, M.I. Baskes, and M.S. Daw, Phys. Rev. B 1986). We find that only a small minority of the alloys exhibit “sluggish” diffusion whereas in the large majority of alloys diffusion is faster and in quite a few cases could be considered “vigorous”. We find that the diffusivity does not correlate with the number of constituents but does correlate very well with the constituent diffusivities and lattice mismatch.