Papers by Author: Y.L. Chiu

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Authors: Y.L. Chiu, W. George Ferguson
Abstract: Nanoindentation technique has been widely used for measuring mechanical properties from a very small volume of material. The hardness measured using the depth sensing nanoindentation technique often decreases with increasing indentation size, the so called indentation size effect (ISE)[1, 2]. It has been generally acknowledged that the ISE in crystalline materials originates from the density change of geometrically necessary dislocations (GND) needed to accommodate a permanent indentation imprint. Conventionally, to characterize an ISE often requires a series measurement of hardness values at different indentation size. Based on the celebrated Oliver-Pharr scheme[3]. We propose a method to derive the ISE from the loading curve of one single indentation test. The application and limitation of the proposed method will be discussed.
Authors: Y.L. Chiu, V. So, Zheng Wei Li
Abstract: In this work, we report our study of the microstructure and mechanical properties of pure Ti, Ti-11Al, Ti-47Al and Ti-6Al-4V nanostructure coatings on AZ91D Mg alloys prepared using DC magnetron sputtering. The fine structures of the coating (see fig. 1 for Ti-6Al-4V coating) are presented. The hardness of the coatings were tested on a CSEM nano-hardness tester with a Berkovich diamond intender. Hardness values were obtained from analyses using the Oliver-Pharr scheme. The hardness of the nanostructure coating increases from about 3.5GPa up to about 6.8GPa when the aluminium concentration increases from zero to 47at.%. Maximum hardness value was found on the Ti-6Al-4V coating, about 7.3GPa. The elastic modulus of the pure Ti coating has the lowest modulus and strain burst “pop-in” has been observed on Ti-47Al coating.
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