30 Years of Nanoindentation with the Oliver-Pharr Method and Beyond: High Temperature & Local Flow Curves
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

Tuesday 8:00 AM
March 1, 2022
Room: 259A
Location: Anaheim Convention Center

Session Chair: Jeffrey Wheeler, Femto Tools Ag; Nathan Mara, University of Minnesota

8:00 AM  
High-temperature Scanning Indentation: A New Technique to Assess Microstructural Changes Along Thermal Ramping: Gabrielle Tiphene1; Paul Baral2; Solène Comby-Dassonneville3; Gaylord Guillonneau1; Guillaume Kermouche4; Jean-Michel Bergheau1; Warren Oliver5; Jean-Luc Loubet1; 1Ecole centrale de Lyon, LTDS UMR CNRS 5513, France; 2Institute of Mechanics, Materials and Civil Engineering, UCLouvain, B-1348, Louvain–la–Neuve, Belgium; 3INSA-Lyon, MATEIS UMR CNRS 5510, 7 Avenue Jean Capelle, 69621, Villeurbanne Cedex, France; 4Mines Saint-Etienne, UMR CNRS 5307 LGF, Centre SMS, F – 42023 Saint-Etienne, France; 5KLA Nanomechanics Inc, Oak Ridge, USA
     Thanks to recent developments in high temperature nanoindentation testing, investigation of thermally activated mechanisms at small length scales can now be conducted [1]. In-situ anisothermal measurements at the micron-scale of hardness, Young modulus and creep properties are now feasible. The development of the High Temperature Scanning Indentation [2] technique, based on a specific high-speed loading procedure, allows quasi-continuous determination of those properties in temperature in only few hours. We focus here on cold-rolled pure aluminum that undergoes static recovery and recrystallization during an annealing thermal cycle. Hardness upon heating and cooling varies in a different manner, pointing out the occurrence of those phenomena upon heating. Part of the observed hardness drop was related to recrystallization, assessed by post-mortem EBSD microstructural characterizations. Modeling of those phenomena was carried out to characterize their kinetics. [1] Baral et al., Materials and Design, (2018)[2] Tiphéne et al., Journal of Material Research, (2021)

8:20 AM  
Nanoindentation to Determine High Temperature Rate Effects in Advanced Nuclear Reactor Steels: Moujhuri Sau1; Zezhou Li1; Eric Hintsala2; Douglas Stauffer2; Laurent Capolungo3; Nathan Mara1; 1University of Minnesota; 2Bruker Nano Inc.; 3Los Alamos National Laboratory
    Nanoindentation is a versatile, high throughput, nondestructive technique for testing mechanical properties of materials at the nano- and micro-scales. Through recent developments in nanoindentation technology, this method can explore the relationship between the microstructural features of materials and their creep deformation responses. Elevated temperature nanoindentation tests were performed on three different reactor steel materials and a reference material– T91 ferritic martensitic alloy, an ODS alloy (MA957) and a FeCrAl alloy (APMT), and austenitic stainless steel (SS347H). We determined the strain rate sensitivity (SRS), activation energy and activation volumes using nanoindentation creep testing on a Bruker Hysitron Vacuum Indenter System, and observe increases in SRS that can be correlated to material microstructure and bulk creep tests. We will explain these behaviors in terms of the dominant diffusion and dislocation-based creep mechanisms, as well as the Portevin-Le Chatelier effect arising from dynamic strain aging at a narrow range of test conditions.

8:40 AM  Invited
Variable Strain Rate Stress-strain Behavior Using Displacement-controlled Spherical Nanoindentation: Jeffrey Wheeler1; 1FemtoTools AG, Furtbachstrasse 4, CH-8107 Buchs/ZH, Switzerland
    Since the work of David Tabor, the promise of the extraction of stress-strain curves from indentation data has drawn extensive interest. However, despite significant progress from several groups in recent years, spherical indentation testing has not yet been widely adopted within the nanoindentation community. This is rather surprising, since spherical indentation offers a simpler, more cost-effective alternative to micro-compression of pillars fabricated by focused ion beam (FIB). One limitation of current techniques is the influence of pop-in displacement bursts on stress-strain curves. This can be overcome by using an intrinsically displacement-controlled indenter, which provides stress-drop information without loss in strain-resolution instead. In this work, the current state-of-the-art in spherical nanoindentation data analysis is reviewed and extended for use on displacement-controlled nanoindentation at variable strain rates.

9:05 AM  
Nanoindentation for Reliable Assessment of Mechanical Flow Curves Under Ambient and Non-ambient Conditions: Verena Maier-Kiener1; Gerald Schaffar1; Anna Ebner1; Daniel Kiener1; 1Montanuniversitaet Leoben
    An appealing idea to material scientists is to characterize the flow behavior of materials with minimal experimental effort while guaranteeing highly reliable results. Nanoindentation is one candidate technique to achieve this objective. Although established as standard method to extract hardness and Young’s modulus, the technique is not yet fully exploited regarding the determination of localized flow curves, since understanding the correlations between mechanical properties obtained by spherical indentation experiments and uniaxial data is extremely challenging. To correctly account for tip imperfections, a calibration procedures originating from fundamental geometrical considerations is applied. This sets the foundation for strain-rate controlled experiments and allows an experimental evaluation of the constraint factor in consideration of the mechanical properties and induced strain, which enables the extraction of reliable flow curves. These protocols are applied at room and elevated temperatures in order to demonstrate temperature effects on the work hardening behavior of different metal microstructures.

9:25 AM Break

9:40 AM  
Measuring Stress-strain Curves of Metals by Nanoindentation with a Frustum: Jennifer Hay1; Marzyeh Moradi1; 1KLA
    A method is presented for measuring the local true stress-strain curve of a metal by nanoindentation with a frustum, assuming the Young's modulus. Stress is smartly proportional to mean pressure; strain is proportional to depth. Beyond the point of full contact, these stress-strain pairs are fit to a power-law form. The yield point, which is prior to full contact, is the intersection between this fit and the linear part of the stress-strain curve (i.e. the given Young’s modulus). Thus, by the end of each indentation test, the true stress-strain curve is presented by automatically patching together these three segments into a whole: (1) From the origin to the yield point: the linear part, (2) From the yield point to the point of full contact: an extrapolation of the power-law fit, and (3) From full contact to the end of loading: measured true stress-strain. The result is quite satisfying and useful.

10:00 AM  
Process-structure-property-performance Relations for High-pressure Cold-sprayed Metals via Nanoindentation Stress-strain Measurements: Bryer Sousa1; Jennifer Hay2; Danielle Cote1; 1Worcester Polytechnic Institute; 2KLA Instruments
    Comprehensive mechanical characterization of cold-sprayed metals is critical as they are increasingly used for solid-state additive manufacturing and repair. Nanoindentation is an attractive, high-throughput technique because it is suitable for small volumes and requires minimal sample preparation. In this work, an emergent nanoindentation method was applied to a range of high-pressure, cold-spray material consolidations made by systematically varied process parameters. The nanoindentation method used a flat-ended conical indenter to measure stress-strain curves and scalars derived therefrom, including yield stress and work-hardening exponent. We discerned processing-structure-property-performance relations for cold sprayed tantalum, steel, aluminum, and other material consolidations with these measurements. Before testing cold-sprayed metals, the flat-punch nanoindentation method was validated by comparing its stress-strain curves with uniaxial tensile curves and spherical nanoindentation curves for several different metals.