Mechanical properties of polycrystalline ceramics by nanoindentation methods: Effect of surface roughness and tip size
Başlık çevirisi mevcut değil.
- Tez No: 400430
- Danışmanlar: PROF. MICHEL W. BARSOUM, PROF. ORI YEHESKEL
- Tez Türü: Yüksek Lisans
- Konular: Metalurji Mühendisliği, Metallurgical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2009
- Dil: İngilizce
- Üniversite: Drexel University
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Malzeme Bilimi ve Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 99
Özet
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Özet (Çeviri)
In this thesis, we principally discussed the characterization of hard, brittle polycrystalline solids using principally NI. We briefly introduced tip types and then focused on spherical tips which were mainly used in all of our experiments. We explained a method to plot S vs. a diagrams. Based on this work, it is obvious that the S vs. a plots are a powerful, and relatively simple, technique to measure the E of polycrystalline ceramics and other hard solids.A distinct advantage to using spherical NI is the fact that one can also obtain NI stress ? strain curves that can be quite informative about the mechanical properties of the materials as compared to the commonly used load ? displacement diagrams. NI stress ? strain curves enable one to determine the elastic and elastic ? plastic regimes.In Chapter 3 and 4, we reported our work on the polycrystalline binary oxides Y2O3, Sc2O3 and Er2O3. The E and H values were measured by using spherical and sharp indenters. The Young's moduli of these solids were determined from S vs a curves. We also plotted the NI stress ? strain curves. These results, in turn, were compared with the hardness values obtained using Berkovich tips. We also measured the Vickers hardness values and compared to those obtained from the NI stress-strain curves and those obtained from the Berkovich tip. The influence of polishing quality on surface roughness and the effect of the latter on the mechanical properties of Sc2O3 and Er2O3 were also examined and reported in Ch. 4. The 75relationship between the polishing quality ? viz. surface roughness ? effective zero point and tip size on the following solids: Y2O3, Sc2O3, Er2O3, B4C, MgAl2O4 and LiTaO3 were discussed in Ch. 5. Based on our results we concluded that:? NI is an excellent way to determine the mechanical properties of polycrystalline ceramics which are brittle solids that cannot be otherwise tested at room temperature.? The E values calculated using spherical indenters were always smaller than those measured by the Berkovich indenter. It follows that sharper tips yield higher E values. The E values of both of all tips, however, were close to those measured by ultrasound, ES.? The H values obtained using the Vickers tip are always lower than those obtained using Berkovich tips. Confirming this notion is the fact that the yield points obtained from the NI stress ? strain curves - a value that can be considered to be the NI spherical“hardness”- is less than the Vickers hardness.? A tip size effect is observed. In general, the smaller radii tips resulted in higher E values than larger ones. The yield points, on the other hand showed quite a bit of scatter. Within that scatter, no tip size effect was observed. The scatter, however, was a strong function of surface roughness, with rough surfaces yielding higher scatter.? The K1C values calculated in this work, except for Er2O3, are in a good agreement with published results in the literature. Calculated K1C values for Er2O3 are approximately 50% below its single crystal values in the literature.? The polishing quality clearly affects the surface roughness of the materials. Finer polishing decreases the furrows and surface roughness, so the tip can better access the true surface of the material. More precise material characterization can be made by this way.76? Smoother surfaces result in less scatter and values of E that are closer to those obtained from ultrasound. The effect of the surface roughness on the NI stress ? strain curves was also investigated. Higher roughness resulted in much more scatter in both the elastic and plastic regions. We observed a bending in the initial section of the 5 ?m radii tip data for the rough polishing. After the fine polishing this bending was significantly reduced.
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