The hot tearing behaviour of magnesium alloys is one of the very important parameters to estimate the alloys actual application. The hot tearing mechanism of different Y content of Mg–Zn–Y–Zr alloys was studied in the present paper. The several important parameters of the mushy zone of MgZn2·5YxZr0·5 ( x = 0·5, 1, 2, 4, 6) alloys were collected by thermal analysis method. The solidification temperature and shrinkage stress during the solidification of MgZn2·5YxZr0·5 alloys were acquired by using the ‘T’ type permanent mould hot tearing testing instrument and the attached computer. The fracture morphology and the cross section of hot tearing regions were observed by scanning electron microscopy. The results shown that the first and the second characteristic temperature of primary crystal nucleation Tn1-cc and Tn2-cc decrease with increasing yttrium content except MgZn2·5Y2Zr0·5 alloy, and the dendritic coherency temperature Tcoh had the same trend, while the temperature difference of the first and the second characteristic temperature of primary crystal nucleation ( Tn1-cc− Tn2-cc) increases slowly with yttrium content. The solid fraction of dendritic coherent, fscoh, of MgZn2·5YxZr0·5 alloys are from 0·38 to 0·74, and the fscoh of MgZn2·5Y2Zr0·5 and MgZn2·5Y6Zr0·5 alloys are relatively lower, while the MgZn2·5Y4Zr0·5 alloy has the highest fscoh. By analysing the effect factors of hot tearing susceptibility of MgZn2·5YxZr0·5 alloys, such as mushy zone properties, the morphology of hot tearing regions and the solidification shrinkage stress curve, the hot tearing mechanism of MgZn2·5YxZr0·5 alloys can be described as follows: with the lower Y content, the main mechanism of hot tearing of MgZn2·5YxZr0·5 alloys is dendritic bridging; with the higher Y content, the main mechanism of hot tearing of MgZn2·5YxZr0·5 alloys is liquid film combined with solidification shrinkage repairing.
The nano amorphous interface is important as it controls the phase transition for data storage. Yet, atomic scale insights into such kinds of systems are still rare. By first-principles calculations, we obtain the atomic interface between amorphous Si and amorphous Sb2Te3, which prevails in the series of Si-Sb-Te phase change materials. This interface model reproduces the experiment-consistent phenomena, i.e. the amorphous stability of Sb2Te3, which defines the data retention in phase change memory, and is greatly enhanced by the nano interface. More importantly, this method offers a direct platform to explore the intrinsic mechanism to understand the material function: (1) by steric effects through the atomic "channel" of the amorphous interface, the arrangement of the Te network is significantly distorted and is separated from the p-orbital bond angle in the conventional phase-change material; and (2) through the electronic "channel" of the amorphous interface, high localized electrons in the form of a lone pair are "projected" to Sb2Te3 from amorphous Si by a proximity effect. These factors set an effective barrier for crystallization and improve the amorphous stability, and thus data retention. The present research and scheme sheds new light on the engineering and manipulation of other key amorphous interfaces, such as Si3N4/Ge2Sb2Te5 and C/Sb2Te3, through first-principles calculations towards non-volatile phase change memory.
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