Deformation Mechanisms, Microstructure Evolution, and Mechanical Properties of Nanoscale Materials: Phase Transformation Plasticity
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Nanomechanical Materials Behavior Committee
Program Organizers: Niaz Abdolrahim, University of Rochester; Matthew Daly, University of Illinois-Chicago; Hesam Askari, University Of Rochester; Eugen Rabkin, Technion; Jeff Wheeler, Femtotools Ag; Wendy Gu, Stanford University
Tuesday 8:00 AM
March 21, 2023
Room: Aqua 300AB
Location: Hilton
Session Chair: Niaz Abdolrahim, University of Rochester; Matthew Daly, UIC
8:00 AM Invited
First Principles Study of Local Phase Transformation in Ni Base Superalloys
: Maryam Ghazisaeidi1; Naga Sri Harsha Gunda1; Michael Mills1; 1Ohio State University
The segregation or depletion of solutes to or from the stacking fault region changes the SFE and further influences dislocation behavior. In the complex composition space of Ni-base superalloys, the segregation of solutes to stacking faults has been shown to bring about the formation of local phases. In other words, a first-order “segregation transition” can occur at the defects when the bulk alloy composition and temperature are in a single-phase range. We use first-principles calculations to systematically study the formation of local phases at superlattice faults. Specifically, we investigate the effect of Nb, Co, and Ti concentrations on the formation of various local phases. In addition, we study the effect of these phases on the subsequent deformation mechanisms. Our results can be used to find an optimized composition, at which the beneficial strengthening effect of local phases can be achieved without precipitation of potentially deleterious phases.
8:30 AM
Measurement of Transformation Stress in Metastable HEAs by Nanoindentation: Yingjie Lu1; Junaid Ahmed1; Matthew Daly1; 1University of Illinois at Chicago
Pop-in events due to stress-induced phase transformations in metastable HEAs have been observed in the load-depth curves of nanoindentation experiments. To quantify the conditions for phase metastability, the transformation stress during pop-in requires measurement. In the present work, we leverage spherical nanoindentation and Hertzian contact mechanics to estimate the transformation stress. The contact area function of the spherical tipped indenter was calibrated and used in indentation strain and stress calculations. The stress-induced transformation mechanism was verified using electron backscatter diffraction analysis.
8:50 AM
In-situ TEM Annealing Reveals Oxide-metal Interface is Initiation Site for Phase Transformation in TiO2 Nanotubes: Jerry Howard1; Hammad Malik1; Brian Van Devener2; Swomitra Mohanty2; Krista Carlson1; 1University of Nevada, Reno; 2University of Utah
Anodically grown titanium oxide nanotubes (NTs) are of great research interest due to their unique physiochemical properties. For many applications, however, heat treatment is required to impart the NTs with a useful crystalline structure. The exact processes which occur in NTs during heat treatment, including the anatase to rutile transition (ART), have not been reported on. Previous studies have largely made use of conventional materials characterization techniques; analyzing bulk samples after annealing has completed. In this study, an in-situ transmission electron microscopy technique was used to observe the morphological and phase changes occurring at the oxide-metal interface of titanium oxide NTs during annealing. This analysis required the use of a novel FIB-based lift out technique. The effects of the metal substrate were characterized by preparing samples both with and without the metal substrate present. Through this analysis, the oxide-metal interface is indicated as the initiation site for the ART.
9:10 AM Invited
About the Plasticity of Metals upon Phase Transformation – A High Temperature Nanoindentation Study: Verena Maier-Kiener1; Lea Lumper1; 1Montanuniversitaet Leoben
Nanoindentation became a versatile tool for assessing local mechanical properties far beyond hardness and modulus. By adjusting standard nanoindentation methods, it was possible to receive measurement protocols such as nanoindentation strain-rate jump or long-term creep tests designed especially to probe thermally activated deformation processes. A further newly introduced field of application for high temperature nanoindentation as a complimentary method is studying the mechanics of plasticity upon bulk phase transformations. In the presented study, bell-bronze Cu20Sn was intensively investigated regarding phase transformations and corresponding local mechanical properties. Within this alloying system various different high-temperature phases were adjusted by different heat treatments accompanied with subsequent quenching. Afterwards these alloys were detailed investigated by different microscopy techniques, XRD as well as high temperature nanoindentation. Two previously unknown meta stable phases were discovered. For all adjusted phases, the local mechanical properties were measured over temperature to shed light into their thermally activated deformation behavior.
9:40 AM Break
10:00 AM
Size Effects on the Stress-induced Martensitic Transformation in Cu-based Shape Memory Alloys: Jose Gómez-Cortés1; María Nó1; Mikel Pérez-Cerrato1; Isabel Ruiz-Larrea1; Tomasz Breczewski1; Jose San Juan1; 1Universidad del Pais Vasco
Shape memory alloys (SMAs) are functional materials exhibiting specific shape memory and superelastic effects, which found number of potential applications in micro and nano technologies. In particular, Cu-based SMAs offer a very good behavior at small scale in comparison with the traditional TiNi alloys. However, the functional properties of SMAs at small scale exhibit several size effects on the stress-induced martensitic transformation.In the present work we present an overview of the size effects observed on the stress-induced transformation in ternary Cu-Al-Ni and Cu-Al-Be SMA as well as in its quaternary alloys. The size effect on the critical stress was quantified through nano compression tests on micro/nano pillars between 2 and 0.25 micrometer in diameter. The comparison of the behavior in ternary and quaternary Cu-base SMAs, allows establishing a universal scaling law for the observed size effects, which is explained through and atomic model for martensite nucleation in confined volumes.
10:20 AM
Stress-assisted Structural Phase Transformation in Molybdenum-based Composites: Lijie He1; Linh Vu1; Zheming Guo1; Ali Shargh1; Niaz Abdolrahim1; 1University of Rochester
Structural phase transformation (PT) mechanism can become operational at high temperature or very high applied stresses and thus suppress sudden failure with minimal uniform macroscopic plastic deformation in nanoporous (NP) metals. For the first time, our results showed that the combination of microstructural features including small (defect-free) ligaments, tortuosity of the structure, and interfaces between core and secondary coating material, will enable a uniform distribution of high internal stresses through the entirety of NP and composite structures that can promote uniform PT and better ductility. PTs in NP/bicontinuous materials can, thus, play a central role in obtaining metal alloys with desired mechanical and functional properties such as improved strength and ductility.
10:40 AM
Characterization of Dislocations in Shape Memory Alloy Using Large Scale MD Simulation: David Farache1; Shivam Tripathi2; Alejandro Strachan1; 1Purdue; 2Istituto Italiano di Tecnologia
Shape memory alloys are of interest in various applications due to their ability to revert to their original shape after large deformations. This effect and superplasticity are governed by a solid-state diffusion-less transformation. Molecular dynamics (MD) simulations have provided an atomic-level picture of the underlying processes but efforts to date focused on defect-free crystals. We characterize the effect of dislocations on the temperature and stress-induced martensitic transformations via large-scale MD. The simulations reveal the impact of line defects on the nucleation and propagation of the martensitic and austenitic transformations as well as in the resulting microstructure, including austenite twins. The simulations also provide insight into the change in martensite start temperatures with sample deformation observed experimentally.
11:00 AM
Probing the Plasticity and Microstructure Evolution of an Icosahedral Quasicrystal i-Al-Pd-Mn at Small Scales: Yu Zou1; 1University of Toronto
Quasicrystalline materials possess a unique structure that is ordered yet not periodic. Despite their special configuration and many useful properties, they are typically very brittle at temperatures below ~75% of their melting points, rendering them difficult to process and often unsuitable for practical implementation. Here, we study the mechanical behavior of a typical icosahedral quasicrystal (i-Al-Pd-Mn) using micro-thermomechanical techniques over the temperature range of 25- 500 °C, which has never been explored before. A few interesting phenomena have been observed, including micro-pillar shrinkage, phase transformations, grain refinement, and thermally induced transitions in deformation behavior (from brittle fracture to serrated plastic flows, and then to homogeneous flows). Furthermore, we discuss the multiple underlying mechanisms on the mechanical behavior of the quasicrystal in this temperature regime, exploring surface evaporation/diffusion, diffusion-enhanced plasticity, dislocation activities, and grain boundary rotation/sliding.