材料期刊网

二十面体准晶（ IQC）相强化的Mg?Zn?Y／RE合金具有优良的室温和高温力学性能，且可通过热变形处理进一步提高其力学性能。但此类Mg合金在铸造和热处理时往往会形成有害的晶体相，从而弱化IQC相的强化作用。准确了解此类Mg合金中的相变类型、序列和温度，尤其是IQC相的变化，对通过优化处理工艺提高材料性能非常重要。为深入了解Mg合金中准晶相变的规律和机制，选用成分为Mg95 Zn4?3 Y0?7的合金作为研究对象，采用原位加热透射电子显微术实时研究了IQC相到面心立方W相Zn3 Mg3 Y2和六方H相Zn3 MgY的相变，及W／Mg和H／Mg界面上生长IQC的固态相变。 IQC→W和IQC→H的相变温度分别为720 K和727 K。金属间化合物准晶一般由液态形成，但原位加热观察发现升温至573 K和593 K时， IQC相颗粒就在六方H相和立方W相的表面上固态外延形核生长。借助像差校正扫描透射电子显微术研究了准晶和晶体间界面的原子结构，从原子尺度解释了金属间化合物准晶在固态条件下的起源。固态准晶相变的研究为认识准晶起源开辟了新天地。

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?Zn3 Mg3 Y2 and H?Zn3 MgY) 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 trans?mission electron microscopy studies were performed to study the phase transformation and underlying mechanisms in a Mg95 Zn4.3 Y0.7 alloy. During in situ heating, IQC was transformed to W and H at 720 K and 727 K, respectively. Interestingly, solid?state formation of IQCs was observed at H/Mg and W/Mg interfaces upon heating to 573 K and 593 K, respectively. The solid?state nucleation and growth of IQCs in crystalline systems are in stark contrast to that occurred in liquids. The a?tomic 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.