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NSYSU

1. Chuang, Wen-Shuo. Deformation mechanisms and sample size effects of Mg-Zn-Y 18R LPSO.

Degree: PhD, Materials and Optoelectronic Science, 2018, NSYSU

With the long-period stacking ordered (LPSO) second phase, a novel Mg-Zn-Y based alloys with excellent mechanical properties have been developed. Because the LPSO phase plays an important role in strengthening, it is urgent to clarify the deformation mechanisms within the LPSO phase. Until now, there have been many research works done on the LPSO structure examination and the deformation mechanism along its growth direction, which is [11"2" Ì0], but all in the mini-meter scales. However, because the grain size of the LPSO is typically in 30 to 150 ï­m, it is essential to shrink the testing sample sizes in order to achieve a clear examination on LPSO single crystals. Moreover, the mechanical properties and the deformation mechanisms on different crystal orientations have not been clarified. In this study, the yield strength as well as the deformation mechanisms of the Mg-Zn-Y 18R LPSO structure with two different orientations, namely, (11"2" Ì0) and (0001), will be systematically examined and analyzed in the micro-meter scale by micropillar compression, and the basic mechanical properties by nanoindentation. As for compressing along [11"2" Ì0], different deformation behavior have been observed between different sample sizes. The prism slip has been observed in smaller micro-pillars while the deformation kink has been observed in larger micro-pillars. The origin of deformation kink has been found out to be the prismatic dislocation slip. According to the Frankâs rule, the interaction between prismatic dislocations would cause the stair-rod dislocations, which would form the kink boundaries and nucleate the basal dislocations to induce the deformation kinks. It indicates that the yield mechanisms in Mg-Zn-Y 18R LPSO single crystal during compressing along [11"2" Ì0] are the same which is proved by using both TEM analysis and lnï³-lnd curves fitting. The different deformation behaviors are caused by the sample size effect. With larger sample sizes, the probability of forming stair rod dislocations becomes higher, resulting in higher probability of forming deformation kinks. Moreover, these results will be compared with those in the literature on the mini-meter scale. As for compressing along [0001], since there are few studies with deformation along [0001], we attempt to figure out the whole deformation mechanism. It has been found that the basal dislocations activate first causing the bending of the micro-pillars. The bending situation results in the formation of prism screw dislocations forming the slip band with 45 degrees with respect to the [0001] loading direction. It is considered that the bending can cause the shear stress along [0001] and would induce the nucleation of prism dislocations along 45 degrees with respect to the [0001] loading direction to form the slip band. This slip band causes the first pop-in shown in the stress strain curves. From our results, the deformation behavior are the same with different sample sizes. Moreover, the sample size effect of the first pop-in stress has also been examined… Advisors/Committee Members: J. C. Huang (committee member), Jason Shian-Ching Jang (chair), C.T. Pan (chair), S.R. Jian (chair), H.K. Lin (chair).

Subjects/Keywords: Mg-Zn-Y alloys; 18R LPSO; micro-compression; sample size effect; deformation mechanism; nanoindentation

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APA (6th Edition):

Chuang, W. (2018). Deformation mechanisms and sample size effects of Mg-Zn-Y 18R LPSO. (Doctoral Dissertation). NSYSU. Retrieved from http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0521118-091514

Chicago Manual of Style (16th Edition):

Chuang, Wen-Shuo. “Deformation mechanisms and sample size effects of Mg-Zn-Y 18R LPSO.” 2018. Doctoral Dissertation, NSYSU. Accessed April 19, 2019. http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0521118-091514.

MLA Handbook (7th Edition):

Chuang, Wen-Shuo. “Deformation mechanisms and sample size effects of Mg-Zn-Y 18R LPSO.” 2018. Web. 19 Apr 2019.

Vancouver:

Chuang W. Deformation mechanisms and sample size effects of Mg-Zn-Y 18R LPSO. [Internet] [Doctoral dissertation]. NSYSU; 2018. [cited 2019 Apr 19]. Available from: http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0521118-091514.

Council of Science Editors:

Chuang W. Deformation mechanisms and sample size effects of Mg-Zn-Y 18R LPSO. [Doctoral Dissertation]. NSYSU; 2018. Available from: http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0521118-091514

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