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Thesis
Mechanical properties of polycrystalline ceramics by nanoindentation methods: effect of surface roughness and tip size
Master of Science (M.S.), Drexel University
Dec 2009
DOI:
https://doi.org/10.17918/etd-3167
Abstract
Nanoindentation, NI, - mainly with sharp tips - is a powerful method for the mechanical characterization of solids. When the indenters are sharp, however, valuable information concerning the all-important elastic-to-plastic transition is lost. Spherical tips, on the other hand, do not suffer from this problem. In this work, we used 1.4 [mu]m and 5 [mu]m radii, R, spherical diamond indenters to measure the moduli, E, and generate NI stress-strain curves of the polycrystalline sesquioxides Y2O3, Sc2O3 and Er2O3. The moduli - measured from harmonic contact stiffness (S) vs. contact radius (a) curves - were found to be weak functions of R and slightly lower than the moduli measured by ultrasound on the same samples used for the NI measurements. This work also shows that surface finish - that was varied and quantified by measuring the surface roughness - is an important factor in determining both the values of E, and the shapes of the NI stress-strain curves, especially near the origin. In all cases, fine polishing yielded results that were closer to the true values as measured by ultrasound. The values of E measured by the Berkovich indenter were less sensitive to surface roughness. When the hardness values measured using the Berkovich and Vickers indenters were compared with the yield points obtained from the NI stress-strain curves the order was: Berkovich, Vickers followed by the yield point. This conclusion is in agreement with previous work on brittle single crystals. Based on this work, we conclude that S vs. a plots are a powerful method to measure the Young's moduli of polycrystalline ceramics and other hard solids. The fact that one also obtains NI stress-strain curves is a distinct advantage over the more commonly used load-displacement curves. The influence of surface roughness, tip size and type are important consideration when characterization of mechanical characterization at the nano-scale.
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Details
- Title
- Mechanical properties of polycrystalline ceramics by nanoindentation methods
- Creators
- Ismail C. Albayrak - DU
- Contributors
- Michel W. Barsoum (Advisor) - Drexel University (1970-)
- Awarding Institution
- Drexel University
- Degree Awarded
- Master of Science (M.S.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Resource Type
- Thesis
- Language
- English
- Academic Unit
- Materials (Science and) Engineering (Metallurgical Engineering) [Historical]; College of Engineering (1970-2026); Drexel University
- Other Identifier
- 3167; 991014632055904721