30 Years of Nanoindentation with the Oliver-Pharr Method and Beyond: On-Demand Oral Presentations
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
Monday 8:00 AM
March 14, 2022
Room: Nanostructured Materials
Location: On-Demand Room
Determining Material Parameters from Nanoindentation Data by Inverse Methods: Alexander Hartmaier1; 1ICAMS Ruhr Univ Bochum
Indentation is a versatile method to assess the hardness of different materials along with their elastic properties. Recently, powerful approaches have been developed to determine material properties like yield-strength, work-hardening rate and even cyclic plastic properties by a combination of indentation testing and computer simulations. The basic idea of these approaches is to iteratively optimize the material parameters in indentation simulations until a minimum in the error between simulation and experiment is achieved. Such inverse methods have been shown to work for macroscopic hardness tests, where the indenter is large compared to the microstructural length scale and for which indentation size effects do not play a significant role. In this work, it is demonstrated that such inverse methods can also be applied to nanoindentation data, even when the microstructural scale is on the order of the nanoindenter scale, if the scale-dependence of the material behavior is properly taken into account.
Length Scale Effects of Nanoindentation on Additively Manufactured Stainless Steel: Kunqing Ding1; Yin Zhang1; David McDowell1; Ting Zhu1; 1Georgia Institute of Technology
Additively manufactured 316L stainless steel exhibits high yield strength and strain hardening due to printing-induced sub-micron dislocation cell structures. Nanoindentation is recently used to probe the mechanical properties of both printed layers and stainless steel base plate with and without annealing treatment. We perform gradient plasticity finite element (GPFE) simulations to capture the nanoindentation size effect. GPFE simulations also enable us to approximately extract the uniaxial stress-strain behavior of printed layers and base plates from their nanoindentation responses at large indenter depths. Our results indicate that printing-induced dislocation cells play a significant role in the nanoindentation responses in both size dependent and independent regimes. This work underscores the interplay of length scale effects due to nanoindentation and printing-induced microstructure.
Understanding Rate-depending Plastic Deformation under Hydrogen Influence through Advanced In-situ Electrochemical Nanoindentation: Anna Ebner1; Verena Maier-Kiener1; 1Montanuniversitaet Leoben
Despite a lot of research activities, hydrogen embrittlement mechanisms are still controversially discussed. Especially the role of plasticity itself is often underestimated. Hence, the investigation of plastic deformation processes under hydrogen influence is a vital field of research. Nanoindentation strain rate jump tests are used in an in-situ electrochemical nanoindentation setup with the aim of determining the thermally activated deformation parameters. Beside reproducible measurements of standard mechanical properties, such as hardness and Young’s modulus, deeper insight in the acting deformation processes can be gained by calculating strain rate sensitivity and activation volume. A measured increase in strain rate sensitivity and a decrease in activation volume can indicate short-range effects, which can lead to a more localized deformation. In combination with optical evaluation methods, like laser confocal microscopy, the plastically deformed zone around the indents and the changes in slip step characteristics under hydrogen charging can be analysed.
Comparison between Long-term Nanoindentation Creep Testing under Constant Load and Constant Pressure: Thomas Chudoba1; 1ASMEC GmbH
Creep effects can be observed during nanoindentation experiments when the load is held constant at maximum force. Attempts to correlate nanoindentation creep curves under constant load with the results of macroscopic creep tests failed because the depth change under load is accompanied by a pressure reduction, while uniaxial creep tests are done under constant stress. Further, the thermal drift is reducing the accuracy for measurements with nanometer resolution.A test methodology has been developed that allows measurements under constant pressure and that considers thermal drift effects. The necessary calculations are done live during the measurement and used to correct force and depth accordingly. Pressure calculation and drift correction are based on dynamic contact stiffness measurements and on the assumption of a constant modulus. Results are presented for several materials and pressure levels and compared with creep results from constant force experiments.
Factors Affecting Nanoindentation Derived Activation Parameters for PLC Effects: Henry Ovri1; Erica Lilleodden1; 1Helmholtz Zentrum Hereon
The relevant atomic species that dynamically age dislocations during deformation and consequently the underlying deformation mechanisms that govern Portevin-Le Chaterlier (PLC) effect are commonly accessed by estimating the associated activation enthalpy, ∆Ea. We recently developed a nanoindentation-based approach that is based on a more theoretically sound phenomelogical model than the conventional uniaxial test based methods. Unlike the latter, the model provides estimates of ∆Ea along with the associated activation volume and attempt frequency at only one temperature. In this talk, we will highlight the influence of strain rate, indentation depth, and indenter geometry on these parameters and discuss the implications of these variables on the utility of the technique for investigations of PLC.
Estimating the Elastic Constants of Pulp Fibers with Nanoindentation: Caterina Czibula1; August Brandberg2; Megan Cordill3; Artem Kulachenko2; Christian Teichert4; Ulrich Hirn1; 1Institute of Bioproducts and Paper Technology, Graz University of Technology; 2KTH Royal Institute of Technology; 3Erich Schmid Institute for Materials Science, Austrian Academy of Sciences; 4Institute of Physics, Montanuniversitaet Leoben
Pulp fibers are extensively used for paper and packaging, but structure-property relations on the fiber scale are complicated and not fully understood. The fiber cell wall consists of different layers with varying thickness, chemical composition, and alignment of cellulose microfibrils, giving them anisotropic mechanical properties. Micromechanical modeling of fiber networks relies on material data of individual fibers. However, due to the fibers’ dimensions, single fiber testing is limited to obtaining the longitudinal elastic modulus. The application of nanoindentation (NI) methods is advantageous because the surface of the fiber can be accessed from different directions to probe the mechanical response along different normals. Here, conventional NI as well as atomic force microscopy-based NI are explored to obtain an estimate of the transverse and longitudinal elastic constants of wood pulp fibers. The results are compared to uniaxial tensile testing.
A Novel Indentation-size-effect-based Nanoindentation Test Method Enabling Smaller Scale Testing for Safer Nuclear Structural Health Monitoring: Rohit Sharma1; Nigel M. Jennett1; Chris D. Hardie2; Alexandra J. Cackett2; 1Coventry University; 2UK Atomic Energy Authority
Low-carbon Nuclear energy provides 10% of global electricity. Periodically, radiation damage is monitored by destructively testing Surveillance samples irradiated by the reactor. A smaller-scale Nanoindentation test would improve safety: reducing sample radioactivity/waste, and allowing more tests. We analyse spherical indentation data (Cu single crystal) from the EMPIR (EU/EURAMET) Strength-ABLE project using the Hou and Jennett (2012) algorithm, which relates hardness to plastic zone size and dislocation-dislocation interaction distance. An input of (easily-measured) indentation size effect, is combined with a measurement of Plastic zone size to give quantified estimates of the absolute dislocation-dislocation interaction distance and the fraction of dislocation density that is mobile; values otherwise very difficult to obtain. When this novel nanoindentation test method is applied to nuclear materials it generates new figures-of-merit to quantify damage that will be valuable for materials selection and for safer structural health monitoring of metal embrittlement by long-term exposure to irradiation.
Hardening Relationship with Hydrogen and Dislocation Structure in FeCr Alloys by In Situ Nanoindentation: Jing Rao1; Subin Lee2; Gerhard Dehm1; María Jazmin Duarte Correa1; 1Max-Planck-Institut für Eisenforschung G; 2Karlsruhe Institute of Technology (North)
Hydrogen embrittlement is a critical issue commonly observed in metallic materials. Here we use a novel in situ set-up built in-house for electrochemical backside hydrogen charging during nanoindentation on ferritic FeCr alloys with high hydrogen diffusivity and low solubility to investigate their changes in mechanical response. A hardening effect, independent of the grain orientation, occurs while the elastic modulus remains constant during hydrogen charging at different conditions. The relative hardness variation follows an initial linear increase with increased hydrogen content until hydrogen absorption and desorption reach a steady state. This hardening effect is verified by an enhanced dislocation density in the cross-section underneath the nanoindentation imprints by transmission electron microscopy and modeled accordingly. A higher chromium content results in a more pronounced hardening effect at the corresponding hydrogen saturation level, suggesting that the substitutional chromium atoms act as flat trapping sites for hydrogen retarding its diffusion and increasing its solubility.