使用带有高角环形暗场探测器的扫描透射电镜研究了Mg?2.1Gd?1.1Y?0.82Zn?0.11Zr合金的铸态组织特征,确认了由晶界向晶内延伸的层片状结构为γ′相的集合体;研究了时效峰值态的Mg?2.1Gd?1.1Y?0.82Zn?0.11Zr合金在总应变控制下的高温(573 K)低周疲劳测试中的力学响应和失效机制.在573 K下,合金在不同的总应变幅控制的循环加载中均表现出了循环软化的特征.扫描电镜的观察结果表明:微观裂纹优先在长周期有序相和基体的界面处形核,并沿基面扩展;分布于晶界处的、块状长周期有序相能抑制裂纹的穿晶扩展.
In as-cast Mg?2.1Gd?1.1Y?0.82Zn?0.11Zr (mole fraction, %) alloy, lamellar microstructures that extend from grain boundaries to the interior ofα-Mg grains are identified as clusters ofγ′ using a scanning transmission electron microscope equipped with a high-angle annular dark-field detector. Under a total strain-controlled low-cyclic loading at 573 K, the mechanical response and failure mechanism of Mg?2.1Gd?1.1Y?0.82Zn?0.11Zr alloy (T6 peak-aging heat treatment) were investigated. Results show that the alloy exhibits cyclic softening response at diverse total strain amplitudes and 573 K. The experimental observations using scanning electron microscopy show that the micro-cracks initiate preferentially at the interface between long-period stacking order structures andα-Mg matrix and extend along the basal plane ofα-Mg. The massive long-period stacking order structures distributed at grain boundaries impede the transgranular propagation of cracks.
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