Pop-ins in Nanoindentations – the Initial Yield Point
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Abstract
The load – displacement curves as obtained by nanoindentations on most metallic and intermetallic materials show discontinuities or pop-ins at load levels below or around 1 mN. These pop-ins mark a sharp transition from pure elastic loading to a plastic deformation of the specimen surface, thus correspond to an initial yield point. On smooth surfaces pop-ins are observed frequently, but not on surfaces with a high roughness. Step edges on the surface are discussed as dislocation sources for the initial yield events. Since the pop-ins mark the transition from elastic to plastic deformation, the elastic loading part can be described by the Hertzian contact model. Discontinuities in the load –displacement curves are observed on nearly all materials, examples are given for c-BN, TiAl, Ti3Al, Cu, and Mo5SiB2. On Mo samples, discontinuities are found sometimes only in the unloading part of the load – displacement curves. The origin of the different pop-in effects are discussed.
Abstract
Die mit Nanoindentierungen auf metallischen und intermetallischen Materialien erzeugten Krafteindringkurven zeigen sehr oft Diskontinuitäten oder Pop-ins bei Kräften im Bereich von ca. 1 mN. Diese Pop-ins markieren einen scharfen Übergang von rein elastischem zu plastischem Verhalten und zeigen daher erstes plastisches Fließen an. Der beginnende elastische Teil der Krafteindringkurven kann mit dem Hertzschen Kontaktmodell beschrieben werden. Pop-ins werden fast immer bei Indentierungen glatter Oberflächen kristalliner Materialien beobachtet, aber nicht auf Oberflächen mit höherer Rauhigkeit. Stufen werden diskutiert als die Orte, wo Versetzungen zu Beginn der Verformung aktiviert werden. Beispielhaft werden hier Experimente an c-BN, TiAl, Ti3Al, Cu und Mo5SiB2 beschrieben, die Diskontinuitäten zeigen. In Mo-Proben werden im Unterschied dazu große Diskontinuitäten in den Entlastungskurven gefunden. Die Ursachen der verschiedenen Pop-in-Mechanismen werden diskutiert.
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M. G. thanks the Alexander von Humboldt Foundation, Bonn for financial support of a research stay at Stanford University in the group of Prof. W.D. Nix where some of the experiments were done. R. Saha from Stanford University is thanked for her support with the nanoindenter measurements. A. Zerr from the Technical University Darmstadt and R. Sakidja and J. Perepezko from the University of Wisconsin, Madison is thanked for supplying the c-BN and Mo–Si–B samples, respectively. Financial support by the Volkswagen-Stiftung is also acknowledged.
References
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© 2001 Carl Hanser Verlag, München
Articles in the same Issue
- Frontmatter
- Editorial
- European Symposium on Nanomechanical Testing
- Aufsätze
- Comparison of Different Hardness Definitions Usable for Micro- and Nanoindentation
- Nanohardness Measurements for Industrial Applications
- Friction Studied with the Scanning Force Microscope
- Laser-Acoustics, a Method for Testing Coatings and Material Surfaces
- Nanoindentation Induced Acoustic Emission Monitoring of Native Oxide Fracture and Phase Transformations
- Deformation Curves of Ta-Silicide Thin Films Obtained in Cyclic Nanoindentation Experiments
- Pop-ins in Nanoindentations – the Initial Yield Point
- The Effect of Temperature and Strain Rate on the Hardness of Al and Al-Based Foams as Measured by Nanoindentation
- A Comparision of Nano-Hardness and Scratch-Resistance on Mohs Minerals
- Assisting an Experimental Investigation by Assessment and Use of a Thermodynamic Description for the Cd–Ge System
- Phase Equilibria and Thermodynamics in the Y2O3–Al2O3–SiO2 System
- The Constitution of Alloys in the Al-rich Corner of the Al–Si–Sm Ternary System
- The Al–Si–C Phase Diagram and Its Use for Microstructural Analysis of MMCp and MMCf Composite Materials
- Surface Segregation and Surface Tension in Liquid Fe–Cu Alloys
- Mitteilungen/Notifications
- Personelles/Personal
- Bücher/Books
- Tagungen/Conferences
Articles in the same Issue
- Frontmatter
- Editorial
- European Symposium on Nanomechanical Testing
- Aufsätze
- Comparison of Different Hardness Definitions Usable for Micro- and Nanoindentation
- Nanohardness Measurements for Industrial Applications
- Friction Studied with the Scanning Force Microscope
- Laser-Acoustics, a Method for Testing Coatings and Material Surfaces
- Nanoindentation Induced Acoustic Emission Monitoring of Native Oxide Fracture and Phase Transformations
- Deformation Curves of Ta-Silicide Thin Films Obtained in Cyclic Nanoindentation Experiments
- Pop-ins in Nanoindentations – the Initial Yield Point
- The Effect of Temperature and Strain Rate on the Hardness of Al and Al-Based Foams as Measured by Nanoindentation
- A Comparision of Nano-Hardness and Scratch-Resistance on Mohs Minerals
- Assisting an Experimental Investigation by Assessment and Use of a Thermodynamic Description for the Cd–Ge System
- Phase Equilibria and Thermodynamics in the Y2O3–Al2O3–SiO2 System
- The Constitution of Alloys in the Al-rich Corner of the Al–Si–Sm Ternary System
- The Al–Si–C Phase Diagram and Its Use for Microstructural Analysis of MMCp and MMCf Composite Materials
- Surface Segregation and Surface Tension in Liquid Fe–Cu Alloys
- Mitteilungen/Notifications
- Personelles/Personal
- Bücher/Books
- Tagungen/Conferences
