Compression of Micro-pillars of a Long Period Stacking Ordered Phase in the Mg-Zn-Y system
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Compression of Micro-pillars of a Long Period Stacking Ordered Phase in the Mg-Zn-Y system Atsushi Inoue1, Kyosuke Kishida1, Haruyuki Inui1, and Koji Hagihara2 1 Department of Materials Science and Engineering, Kyoto University, Sakyo-ku, Kyoto, 606-8501 JAPAN 2 Department of Adaptive Machine Systems, Osaka University, 2-1, Yamada-Oka, Suita, Osaka, 565-0871, JAPAN ABSTRACT Deformation behavior of an 18R-type long period stacking ordered (LPSO) phase in the Mg-Zn-Y system was studied by micro-pillar compressions of single crystalline specimens prepared by focused ion beam (FIB) technique as a function of loading axis orientation and specimen dimensions. When the loading axis is inclined to the basal plane of the LPSO phase by 42°, basal slip of (0001)-type is activated irrespective of the specimen dimensions. When the loading axis is parallel to the basal plane, the formation of thick deformation bands are observed for all specimens tested. Strong size-dependence of yield stress values is observed for both types of micro-pillar specimens with different loading axis orientations. INTRODUCTION Recently, a new type of intermetallic phases with long-period stacking-ordered (LPSO) structures has been found in Mg-TM (transition metal)-RE (rare earth) ternary alloys and studied extensively since it has been considered as one of the key factors for endowing the Mg-TM-RE ternary alloys with both high strength and high ductility simultaneously [1-3]. However, inherent characteristics of the LPSO phases including crystal structure and deformation mechanism are largely unsolved [1-3]. We have recently studied the crystal structure of some Mg-TM-RE alloys by atomic resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and have revealed that the crystal structure of the LPSO phase in the Mg-Zn-Y ternary system is characterized by a periodic arrangement of stacking faults within the hcp stacking of parent Mg and also by enrichment of TM and RE atoms in four atomic layers adjacent to the stacking fault as illustrated in Figure 1 [4-8]. These characteristics of the crystal structure imply that inherent deformation behavior of the LPSO phase is strongly anisotropic. As for the deformation behavior of single-phase LPSO phases, only limited studies using directionally solidified (DS) ingots composed of plate-shape grains with their basal planes being nearly perpendicular to the growth direction are available so far and they suggested that the basal slip is the dominant deformation mode in the LPSO phase, whereas abundant deformation kinking occurs when a stress is loaded parallel to the growth direction [9,10]. Studies using single crystalline ingots have never been carried out mostly because it is quite difficult to fabricate single crystals of the Mg-Zn-Y LPSO phases. In the present study, micro-pillars of single crystalline Mg-Zn-Y LPSO phase with two loading axis orientations being parallel or inclined to the basal plane were prepared from the DS ingot of the 18R-type LPSO phase by focused
