Phase Transformations and Microstructural Evolution: Shape Memory Alloys
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Phase Transformations Committee
Program Organizers: Ashley Paz y Puente, University of Cincinnati; Mark Aindow, University of Connecticut; Sriswaroop Dasari, Idaho National Laboratory; Ramasis Goswami, Naval Research Laboratory; Megumi Kawasaki, Oregon State University; Eric Lass, University of Tennessee-Knoxville; Joshua Mueller, Michigan Technological University; Eric Payton, University of Cincinnati; Le Zhou, Marquette University
Tuesday 2:30 PM
March 21, 2023
Room: 25C
Location: SDCC
Session Chair: Eric Payton, University of Cincinnati
2:30 PM Invited
Unexpected Mechanical and Functional Behavior in Shape Memory Alloys Beyond Shape Memory and Superelasticity: Ibrahim Karaman1; 1Texas A&M University
Reversible martensitic transformation in shape memory alloys (SMAs) leads to well-known shape memory and superelasticity effects. Recently, we have achieved a number of new and unique functionalities in these materials by engineering microstructure, crystallographic texture, level of structural disorder, and their interactions with martensitic transformation. Alloys with tunable thermal expansion coefficients were created through crystallographic texturing by thermo-mechanical processing. This enables Invar effect and negative thermal expansion in a very wide temperature range. Strain glass and spin glass behaviors were observed in the same magnetic SMA by controlling the martensitic transformation and its frustration through changing structural disorder. We demonstrated that thermal and electrical conductivity can change significantly and reversibly upon martensitic transformation, which opens opportunities in thermal logic device applications. These examples show that reversible martensitic phase transformation can be used as an engineering tool to tailor the properties of materials as a versatile method to create “designer” materials.
3:00 PM
Mechanisms of Shock Strength Exhibited by a Nickel-Rich Nickel-Titanium-Hafnium Alloy: Tyler Knapp1; Aaron Stebner1; 1Georgia Institute of Technology
Ni-rich NiTiHf alloys exhibit very high strengths and good quasi-static indentation resistance and rolling contact fatigue performances. To determine whether these properties are maintained at high rates of loading, in-situ and recovery flyer plate impact shock experiments were performed on a Ni54Ti45Hf1 alloy at impact velocities ranging from approximately 150 (2.5 GPa) to 700 m/s (12.40 GPa). Analysis of Ni54Ti45Hf1 samples indicated less cracking was observed to emanate from spall failures resulting from impact velocities greater than 250 m/s (4.23 GPa), concurrent with observations of intragranular microbands. Analyses of the mechanical responses showed clear evidence that martensitic phase transformation occurred upon shock compression and reversed upon stress release, yet analyses of these microbands showed no evidence for retained martensite and that nanoprecipitates within the microbands dissolved. These results show that strain-rate dependence of these SMAs under shock loading are not only governed by expected physics of rate-dependence of the martensitic transformations themselves, but also enhanced by plastic deformation mechanisms that result in precipitate dissolution.
3:20 PM Cancelled
Mean-field Approach for High-temperature Shape Memory Alloys: Jean-Briac le Graverend1; 1Texas A&M University
Based on the recently developed crystal-plasticity model on a high-temperature shape memory alloy (NiTiHf), a mean-field approach using the "beta rule" is employed. The beta rule is modified to account for the phase transformation phenomena. Full-field simulations using a representative volume element (RVE) and a crystal-plasticity finite element model (CPFEM) are carried out for actuation from 300 to 500C and a stress of 500 MPa. Results show that the beta rule can predict the material's overall response.
3:50 PM Break
4:10 PM
Low-fatigue Ti-based Shape Memory Alloy for Bulk Elastocaloric Material: Wook Ha Ryu1; Ji Young Kim1; Eun Soo Park1; 1RIAM, Seoul National University, South Korea
Cooling system utilizing elastocaloric material has been recognized as a promising alternative to the vapor compression system, owing to the high coefficients of performance. In this study, we developed a bulk Ti-based superelastic alloy that exhibits mechanical and functional low-fatigue properties. We investigated the elastocaloric effect (temperature change) and strain hysteresis according to reversible stress-induced martensitic phase transformation of the TiNiCu-based multi-component alloy. According to the solidification path by casting in the composition in which Cu is supersaturated, nano-sized precipitates forming a coherent interface with both martensite and austenite phases can be uniformly dispersed in the grain. This methodology is expected to be used as a useful guide for controlling microstructures by dispersing nano precipitations in cast alloys. In addition, this study can be applied to the design of high efficient heat exchange system for home appliances and other products such as refrigerators.
4:30 PM
Cyclic Degradation of Superelasticity of Fe-Mn-Al-Ni Shape Memory Alloy Studied Complementary In Situ Characterization Techniques: Robert Lehnert1; Moritz Müller2; Malte Vollmer3; Philipp Krooß3; Thomas Niendorf3; Horst Biermann1; Anja Weidner1; 1Technische Universität Bergakademie Freiberg; 2Universität Bergakademie Freiberg; 3University of Kassel
The superelasticity of iron-based shape memory alloys is manly determined by microstructural features like grain boundaries, precipitation size or crystal orientation and morphology. Also the interaction of different martensite variants or the interaction of dislocations with the austenite/martensite interface are known to result in a functional degradation. Fe-Mn-Al-Ni and Fe-Ni-Co-Al-Ti single and bicrystals under tensile and compressive loading were used to study functional fatigue with a combination of complementary in situ characterization techniques, e.g. acoustic emission technique (AE), digital image correlation (DIC), high resolution electron backscatter diffraction (HR-EBSD), electron contrast channeling imaging (ECCI) and infrared thermography (IR-TG). The acoustic data showed a decrease in intensity with increasing number of deformation cycles and was interpreted using the information from the in situ observations. In addition, an asymmetry of the acoustic signals during the forward and the backward martensitic transformation could be observed which is related to the dislocation formation. The pinning effect of the dislocations leads to a reduction in the packet density of the retransforming martensite, which results in a lower amplitude of the AE signals indicating the functional degradation.
5:10 PM
Investigating the Effect of L-PBF Process Parameters on 3D Printed Nitinol Part Properties: Josiah Chekotu1; Dermot Brabazon1; 1Dublin City University
Laser Powder Bed Fusion (L-PBF) is an effective method to fabricate Nitinol with desirable functional and mechanical properties. The process parameters and thermal gradients are critical for obtaining the correct phase structure for shape memory capabilities. In this work, multiple Nitinol samples were 3D printed with varying laser power, scan speed, hatch spacing and layer thickness. The energy densities and thermal gradients were found to influence the physical, mechanical and thermal characteristics of the samples. Mechanical characteristics of the printed samples were investigated through cyclic compression and impact testing. The strain recoveries and latent heat regenerations were monitored using Digital Image Correlation and IR thermal imaging techniques. Thermal expansion properties were investigated via dilatometry. The microstructure, phase properties, and phase transformation behavior were also explored through SEM/EDX, nanoindentation, XRD, DSC, and EBSD. This study aids to fabricate Nitinol parts with tailored mechanical and functional properties.
4:50 PM Cancelled
A New Crystal Plasticity Modeling Framework for Fully Implicit Time Integration of Coupled Phase Transformation and Slip in Shape Memory Alloys: Rupesh Kumar Mahendran1; Surya Kalidindi1; Aaron Stebner1; 1Georgia Institute of Technology
A crystal-plasticity based rate-dependent framework is developed for capturing the coupled phase transformation-slip deformation modes at the crystal-scale in NiTi shape memory alloy using a fully-implicit time integration scheme. The computational procedures developed in this work have been successfully incorporated as a user material subroutine (UMAT) in the commercial finite element code ABAQUS Standard. They have been demonstrated for both habit plane variants (HPVs) and lattice correspondence variants (LCVs). Specifically, a new flow rule is derived for the LCV model that incorporates the entire deformation gradient (including the rotational component) for the phase transformation. The predictions from our simulations are also compared against previously published experimental data in literature for single and polycrystalline representative volume elements (RVE) at various temperatures. The computational benefits of the current numerical implementation of the model is demonstrated and compared against previously reported models.