Phase Stability in Extreme Environments: Stress Induced Transformations and Mechanical Properties in Extreme Environments
Sponsored by: TMS Structural Materials Division, TMS Materials Processing and Manufacturing Division, TMS: Corrosion and Environmental Effects Committee, TMS: Nuclear Materials Committee, TMS: Phase Transformations Committee
Program Organizers: Andrew Hoffman, Catalyst Science Solutions; Kinga Unocic, Oak Ridge National Laboratory; Janelle Wharry, Purdue University; Kaila Bertsch, Lawrence Livermore National Laboratory; Raul Rebak, GE Global Research

Thursday 8:30 AM
March 23, 2023
Room: 27A
Location: SDCC

Session Chair: Caleb Clement, Westinghouse Electric Company; Kelvin Xie, Texas A&M University


8:30 AM  Invited
Taming the Pseudoelastic Response of Nitinol Using Ion Implantation: Peter Anderson1; Alejandro Hinojos1; Daniel Hong1; Hariharan Sriram1; Chao Yang2; Janelle Wharry2; Xuesong Gao1; Khalid Hattar3; Nan Li4; Jeremy Schaffer5; Yunzhi Wang1; Michael Mills1; 1The Ohio State University; 2Purdue University; 3Sandia National Labs; 4Los Alamos National Labs; 5Fort Wayne Metals
    Implantation of Ni50.5Ti49.5 wire with 30 MeV Ni6+ ions at doses (< 0.1 DPA) typically smaller than employed in the literature is shown to systematically alter the pseudoelastic response, with extrema in Berkovich nanoindentation load (+50%), hysteresis (−60%), and recoverable displacement (−19%) occurring at ~ 3.6 μm below the implantation surface. These extraordinary values are attributed to ~ 10 to 20 nm amorphous clusters that constrain the stress-induced B2-B19′ phase transformation. This is substantiated by phase field simulations of crystalline-amorphous composites and molecular dynamics simulations of crystalline-vacancy cluster composites showing the spatial refinement of martensite created by nm-scale defects. The results suggest that ion implantation may potentially expand the processing and performance space for NiTi, by creating amorphous defects at smaller length scales than dislocation substructures produced by conventional deformation processing.

9:00 AM  Invited
Grain-subdivision-dominated Microstructure Evolution in Shear Bands at High Rates: Kelvin Xie1; 1Texas A&M University
    Shear banding is an important deformation and failure mechanism in metallic systems, especially at high-rate straining. Dynamic recrystallization was often reported to account for the refined microstructure of shear bands but rarely confirmed using direct quantitative measurement. Here, we employ quantitative precession electron diffraction analysis to uncover shear band microstructure in pure titanium. The results reveal that the microstructure is dominated by early stages of grain subdivision process. Dynamic recrystallization is not as prevalent as perceived conventionally. No alpha-to-beta transformation was observed. Our results offer key insights into understanding shear banding and highlight the need for quantitative analyses of shear band microstructure.

9:30 AM  
Heat Treatment Design of Inconel 740H Superalloy for Microstructure Stability and Creep Properties Enhancement: Dong-Min Kim1; Cheol-Hyeok Yang1; Hyun-Uk Hong1; Hi-Won Jeong2; 1Changwon National University; 2Korea Institute of Materials Science
    In this study, three heat treatment conditions selected from various heat treatment candidates for Inconel 740H, which are considered as materials for in A-USC steam turbines, were exposed to long-term thermal condition at 750℃ up to 5,000 hours. The stability and mechanical characteristics of heat-treated microstructure were examined, and the optimal heat treatment to maximize creep property was derived through creep test (750℃/270 MPa). It was confirmed that the content of Cr was concentrated at the boundary of MC carbide without a specific orientation relationship at 750°C/270 MPa creep, and this was the result of phase transformation by the reaction of MC + γ → M23C6 + γ'. Thus, MC carbide has high resistance to cracks because its temperature and stress during creep contribute to decomposition for phase transformation rather than initiation. Therefore the higher the fraction of the MC carbide, the more advantageous it is to the creep property.

9:50 AM  
Investigation of Effect of Stress on Laves Phase Precipitation and Growth in Creep-ruptured Grade 92 Steel: Emily Proehl1; Steven Zinkle1; Lizhen Tan2; Ying Yang2; David Sprouster3; Weicheng Zhong2; 1University of Tennessee-Knoxville; 2Oak Ridge National Laboratory; 3Stony Brook University
    Improved thermal efficiency of fossil and nuclear power plants necessitates materials with high creep strength, such as Grade 92 (G92) steel. The creep resistance of G92 steel is enhanced by precipitate phases, notably M23C6 (M=Fe, Cr), MX (M=V, X=C, N), and Laves phase (Fe2W, Fe2Mo). Temperature effects corresponding to Laves phase precipitation and creep lifetime are well-documented; fine-scale precipitates initially retard secondary creep but expedite tertiary creep upon coarsening. The effect of stress on Laves phase precipitation and its impact on creep life is less known. To investigate this effect, G92 steel samples were creep tested at 550 – 650°C and 90 – 260 MPa. The Laves phase distribution was investigated via SEM-BSE imaging, and the phase fraction and lattice parameters were quantified via synchrotron transmission XRD. Neutron diffraction residual stress analysis was performed to quantify the recovery in the creep-ruptured samples and correlate it with the Laves phase distribution.

10:10 AM Break

10:25 AM  Invited
Decoupling Irradiation Effects on Unusual Deformation Mechanisms in Alloy 625: Caleb Clement1; Janelle Wharry1; 1Purdue University
    The objective of this talk is to decouple the effects of different irradiation-induced defects on deformation-induced martensitic transformations in Ni-base superalloy 625 (nominally Ni-23Cr-8Mo). This decoupling study is accomplished by a series of irradiations: fast neutrons to 1 dpa at 400ºC, 2 MeV protons to 1 dpa at 500°C to create a dislocation loop-dominated microstructure, 400 keV He+ to 1015 ions/cm2 for a cavity-dominated microstructure, and a dual-beam irradiation emulating the neutron irradiation. Three principal low-zone grain orientations, namely 001, 101, 111, are identified using scanning electron microscopy with electron backscatter diffraction (SEM-EBSD). The identified grains are then nanoindented, and the deformation microstructure is examined using high-resolution transmission electron microscopy (HR-TEM). The results are discussed in the context of the contribution of each defect to the free energy of the system and driving force for transformation.

10:55 AM  Invited
The Impact of Short-order Order on Deformation Phase Transformation and Microstructure Evolution in Multi-principal Element Alloys: Hangman Chen1; Mingjie Xu1; Xin Wang1; Enrique Lavernia1; Xiaoqing Pan1; Penghui Cao1; 1University of California, Irvine
    Mechanistic prediction of mechanical behaviors of materials requires a fundamental understanding of the underpinning mechanisms. We will present our findings of deformation processes at atomistic to nanoscopic length scales in multi-principal element alloys, using multiscale atomistic simulations coupled with in-situ testing and characterization. The results elucidate the deformation mechanisms, phase transformation, and nano-/micro-structure evolution in CrCoNi, underlying its extraordinary mechanical performance. Specifically, we integrate atomistic modeling, in-situ SEM, and TEM characterization to understand the role of short-range order on dislocation slip, twinning, and martensitic transformation. The microstructure and local strain evolution resulting from these deformation processes be discussed.

11:25 AM  
Effect of Annealing Temperature on the Structure and Mechanical Properties of a Single-phase WFeNiMo Multi-principal Element Alloy Film: Zahidur Rahman1; Michael Detisch1; John Balk1; 1University of Kentucky
    The equimolar WFeNiMo multi-principal element alloy (MPEA) has a multiphase microstructure consisting of a BCC dendritic phase and a rhombohedral μ phase dispersed in a continuous FCC matrix. To understand and improve the mechanical properties of this MPEA, the thermomechanical behavior of each individual phase must be properly characterized. A magnetron sputtering system was used to deposit a single-phase FCC W0.125Mo0.375FeNi alloy film on (0001) c-plane sapphire substrate. To study the structural properties during annealing at increasingly higher temperatures starting from 300˚C, X-ray diffraction analysis was employed and the crystal phase(s) were characterized. Cross-section film imaging revealed the effect of annealing temperature on the grain size through the film. Microstructural characterization was complemented by experiments in a wafer curvature instrument to understand the evolution of stress during annealing. Combined with nanoindentation at elevated temperatures, these results provided a deeper understanding of the stability and mechanical behavior of the FCC phase.

11:45 AM  
Oxidation Effects in High-temperature Shape Memory Alloys: Tom Ralph1; Jean-Briac le Graverend1; 1Texas A&M University
    Oxidation has a large effect on phase transformation because oxidation leads to a portion of the material that is not transforming the same way anymore. TGA experiments on NiTiHf samples were performed at 700C for different durations ranging from 10 to 100h. DSC experiments were then performed on those samples to characterize the effects of oxidation on the phase transformation characteristics. The phase-transformation degradation was correlated to the amount of oxidation.