30 Years of Nanoindentation with the Oliver-Pharr Method and Beyond: LIVESTREAMED SESSION: Thin Films & Confinement Effects
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Nanomechanical Materials Behavior Committee
Program Organizers: Verena Maier-Kiener, Montanuniversitaet Leoben; Benoit Merle, University of Kassel; Erik Herbert, Michigan Technological University; Samantha Lawrence, Los Alamos National Laboratory; Nigel Jennett, Coventry University

Thursday 8:30 AM
March 3, 2022
Room: 204B
Location: Anaheim Convention Center

Session Chair: Benoit Merle, University of Kassel; Andrea Hodge, University of Southern California

8:30 AM  Invited
Analyzing Thin Film Strength and Thermo-mechanical Behavior by Wedge Indentation and Bi-metal Beams: Daniel Kiener1; Markus Alfreider1; Benjamin Seligmann1; 1University of Leoben
     Nanoindentation was developed as method of choice to analyze thin films and surface layers. Several years later, focused ion beam (FIB) machined micro pillars were developed to eliminate the constrained deformation under the indenter tip to facilitate mechanical interpretation of confined volume plasticity.Here, we utilize FIB technology to prepare cross-sectional lamellas and bi-metal beams, which are subsequently wedge indented or thermo-mechanically loaded in-situ in a scanning electron microscope at ambient and elevated temperatures. The quasi-2D wedge indentation allows testing of the thin film on a substrate, with direct access to the actual contact area and the flow field under the indenter wedge by digital image correlation. The bi-metal beams facilitate local determination of thermal and residual stresses as well as their evolution with thermal cycling. Combining these novel nanoindentation-derived testing techniques, we attempt to provide a new strategy to access thermo-mechanical properties of thin films.

8:55 AM  
An Improved Technique for Accurate Mechanical Characterization of Free-standing Films and Its Applications: Gang Feng1; Lu An1; Dong Zhou1; Bo Li1; 1Villanova University
    Freestanding films (FFs) enable promising applications. To design reliable FF-based devices, it is essential to know the FFs’ mechanical properties. The most common testing method is nanoindentation of a suspended FF. However, rigorous mechanics models are required to analyze the mechanical measurements. In this study, we demonstrate significant issues associated with existing models. A new improved analytical model is developed, matching nicely with finite element analysis. More importantly, all previous studies are based on the load-displacement relation which is assumed to be elastic, and this assumption has commonly been overlooked and induced serious issues. In this study, a new methodology is developed, which can accurately determine not only the elastic properties (modulus and prestrain) but also the plastic properties (strength). We believe that this new analytical model and new methodology will enable much more accurate mechanical characterization of any FFs, particularly 2D materials.

9:15 AM  Invited
Mechanics of Non-equilibrium Thin Films: Graham Cross1; 1Trinity College Dublin
    Compression of a supported thin film by a precision-aligned, flat micro-punch at extremely high aspect ratios approximates uniaxial strain up to moderate strain while simulating nanoimprint forming processes at high strain. For the first case, we show how this “Layer Compression Test” allows direct, assumption-free measurement of intrinsic stress-vs-strain for soft matter materials down to the 10’s nm scale. Combined with synchrotron-based scanned X-ray microscopy, we present measurements of isothermal polymeric plastic flow in confined to extruded conditions exhibiting homogeneous, defect-free densification that violates the notion of thermal ageing reversal postulated as a general outcome of large shear in disordered matter. Our results contrast with rejuvenation reported for bulk metallic glass macro-scale specimens subject to triaxial compression, agreeing instead with scattered observations of compactification during eg. calendaring in the polymer mechanics literature. We further report structure-property relations of advanced 2D nanocomposites formed by additive manufacturing techniques measured by the technique.

9:40 AM  
Nanomechanical Evaluation of Porous Polymeric Thin Films: Robert Green-Warren1; Luc Bontoux1; Zongling Ren2; Noah MacAllister1; Shalaka Tendolkar1; Lin Lei1; Jae-Hwang Lee2; Assimina Pelegri1; Jonathan Singer1; 1Rutgers University; 2University of Massachusetts
    Recent advances in thin film synthesis have led to widespread adoption of porous thin films. Applications such as selective membranes for microfiltration systems, encapsulation of biomedical micro/nanodevices, and thermal barrier coatings for microelectronic devices lend themselves well to the study of thin films. Further, polymer thin films can be more advantageous thantheir ceramic and metallic counterpartsfor reasons including a higher surfacearea-to-volume ratio, bioresorbance, and relatively lower costs. However, there is a dearth of information available describing the mechanical response of these materials. This work provides an exploration of the nanomechanical properties of porous polymer films produced by self-limiting electrospray deposition (SLED). This novel technique provides for facile tuning of a variety of microscopic properties of thin films of porous materials, including characteristic length scale, composition, and density, leading to high-throughput analysis that can provide insights to the macroscopic bulk analogs of these materials.

10:00 AM Break

10:20 AM  Invited
Mechanical Deformation in Nanomultilayers: Andrea Hodge1; 1University of Southern California
     Nano multilayers (NMs) consist of alternating layers of materials with thicknesses on the order of nanometers and typically display many attractive properties which are attributed to the fact that, as the layer thicknesses decrease, the individual layer behavior changes and the interface volume increases. In general, studies on the mechanical behavior of NMs have been focused mostly on metal systems, followed by metal/ceramic systems and even fewer studies on ceramic multilayers. In this study, we present a comprehensive microstructural evaluation of metal and ceramic multilayers with various layer thicknesses and compositions in order to elucidate on the role of their interfaces during mechanical deformation. Several NM configurations including SiO2/TiO2, AlN/SiO2, AlN/Ag, Cu/Nb, Mo/Au and Hf/Ti will be presented. The role of bilayer thickness and composition is evaluated in both compression and tension using nanoindentation and micro-tensile tests.

10:45 AM  
Bulk Metallic Glass Ductility Trends Are Revealed by High Data Rate Experiments: Jordan Sickle1; Wesley Higgins2; Wendelin Wright3; George Pharr2; Karin Dahmen1; 1University of Illinois; 2Texas A&M University; 3Bucknell University
    Faster materials testing methods are needed to quickly determine the ductility of materials. Here we use experiments and modeling to develop a new method to measure the relative ductility in bulk metallic glasses using nanoindentation with high-rate data acquisition. The analysis extracts a single experimental parameter determined from jumps in the load-displacement curves and ranks the compositions accordingly. This method is ideally suited for rapidly scanning libraries of new metallic glass compositions for relative ductility. We show how the method works and that it is remarkably robust to changes in experimental methodology.

11:05 AM  
Application of Nanoindentation Strain Rate Jump Tests to Measure Strain Rate Sensitivity of Single Crystal Tungsten and Microcrystalline Cellulose: Kevin Schmalbach1; Albert Lin1; Daniel Bufford2; Chenguang Wang1; Changquan Calvin Sun1; Nathan Mara1; 1University of Minnesota; 2Sandia National Laboratories
    Nanoindentation has become an important tool for the mechanical characterization of bulk materials and thin films, especially due to the relative ease of sample preparation. The strain rate sensitivity of materials can be assessed by analyzing the change in material hardness, as determined by the Oliver-Pharr method, during a change in the indentation strain rate. Presented here is a GUI-based tool for creating the indentation load function and standardized, openly-available method for analyzing the data. The methodologies are first demonstrated on single crystal tungsten for simplicity and to compare to literature, showing comparable results. They are further applied to a more complex system, microcrystalline cellulose. Despite the additional polycrystalline nature and the presence of voids and pores in the sample, the data analysis procedures provide consistent results and show promise for use in additional systems for facile measurement of strain rate sensitivity and activation volume.

11:25 AM  
Size-dependent Indentation Behavior and Geometrically Necessary Dislocation Structures of Single-crystalline Tungsten: Jin Wang1; Ruth Schwaiger1; 1Forschungszentrum Juelich GmbH
    The hardness of single-crystalline tungsten exhibits a pronounced dependence on the indentation depth, which is know as the indentation size effect (ISE). For the case of single-crystalline tungsten, the increase of the hardness with decreasing depth cannot be described by the Nix-Gao model over the full depth range. The model overestimates the hardness for depths <300 nm. Assuming different dislocation distributions in the different depth regimes, the observed behavior can be well captured. Furthermore, the geometrically necessary dislocation (GND) structures were analyzed based on plane strain indentation and transmission Kikuchi diffraction. The different characteristics of the GND distributions determined using the Nye-Kröner tensor can be explained by the evolving kink-pair structure with increasing indentation depth. Our findings corroborate the two regimes of the ISE. In this presentation, we will discuss the evolution of the GND structures and introduce a modification to the classical Nix-Gao model capturing the full depth regime.