Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences
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DOI:
10.7502/j.issn.1674-3962.2016.05.03
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Abstract:
Mg-Zn-Y/RE alloys show excellent mechanical properties at both ambient and elevated temperatures due to the presence of icosahedral quasicrystal (IQC) phases. Thermomechanical processing can further improve the mechanical properties of this kind of Mg alloys. However, deleterious crystalline phases (such as W-Zn3Mg3Y2 and H-Zn3MgY) can be formed during solidification or post processing at certain temperatures, impairing the strengthening effect of IQC. The nature, sequence and corresponding temperature of the transformation of IQC phase are still unclear so far. In situ transmission electron microscopy studies were performed to study the phase transformation and underlying mechanisms in a Mg95Zn4.3Y0.7 alloy. During in situ heating, IQC was transformed to W and H at 720K and 727K, respectively. Interestingly, solid-state formation of IQCs was observed at H/Mg and W/Mg interfaces upon heating to 573K and 593K, respectively. The solid-state nucleation and growth of IQCs in crystalline systems are in stark contrast to that occurred in liquids. The atomic level mechanism of solid-state transformation from crystals to IQCs was discussed, based on atomic resolution studies on interfaces between IQCs and crystals. The solid-state formation of IQCs opens a new window on understanding the origin of IQCs.