文章信息/Info

Title:

Quasicrystal and related phase transformations in Mg alloys

作者:

楊志卿; 劉建方; 葉恒強

中國科學院金屬研究所 沈陽材料科學國家（聯合）實驗室

Author(s):

YANG Zhiqing;  LIU Jianfang;  YE Hengqiang

Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences

關鍵詞:

Mg合金; 準晶; 相變; 顯微結構; 界面; 電子顯微學

DOI:

10.7502/j.issn.1674-3962.2016.05.03

文獻標志碼:

A

摘要:

二十面體準晶（IQC）相強化的Mg-Zn-Y/RE合金具有優良的室溫和高溫力學性能， 且熱變形處理能進一步提高其力學性能。但此類Mg合金中鑄造和熱處理時往往還形成有害的晶體相，從而弱化IQC相的強化作用。準確了解此類Mg合金中的相變類型、序列和溫度，尤其是IQC相的變化，對通過優化處理工藝提高材料性能非常重要。為深入了解Mg合金中準晶相變的規律和機制，選用成分為Mg95Zn4.3Y0.7的合金作為研究對象，采用原位加熱透射電子顯微術實時研究了IQC相到面心立方W相Zn3Mg3Y2和六方H相Zn3MgY的相變，及W/Mg和H/Mg界面上生長IQC的固態相變。IQC→W和IQC→H的相變溫度分別為720K和727K。金屬間化合物準晶一般由液態形成，但原位加熱觀察發現升溫至573K和593K時，IQC相顆粒就在六方H相和立方W相的表面上固態外延形核生長。借助像差校正掃描透射電子顯微術研究了準晶和晶體間界面的原子結構，從原子尺度解釋了金屬間化合物準晶在固態條件下的起源。固態準晶相變的研究為認識準晶起源開辟了新天地。

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.