Revisited precipitation process in dilute Mg-Ca-Zn alloys
Revisited precipitation process in dilute Mg-Ca-Zn alloys
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DOI：
10.1016/j.actamat.2023.119072
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发表时间：
2023-06
期刊：
影响因子：
9.4
通讯作者：
Z.H. Li;D. Cheng;K. Wang;E. Hoglund;J. Howe;B. Zhou;T. Sasaki;T. Ohkubo;K. Hono
中科院分区：
文献类型：
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作者：
Z.H. Li;D. Cheng;K. Wang;E. Hoglund;J. Howe;B. Zhou;T. Sasaki;T. Ohkubo;K. Hono
为了深入了解可热处理Mg-Ca-Zn合金的析出过程，我们利用像差校正扫描透射电子显微镜、原子探针断层扫描和第一性原理计算，重新研究了Mg-0.3Ca-0.6 Zn （at.%）稀合金在200°C等温时效过程中的析出过程。峰时效条件下，在(0002)α面上形成单层gp区，转变为厚度为单胞高度的三原子层η "和η'板。然后，η'板成对地形成，在板之间有能量有利的4-5个纯镁原子层。虽然这一转变路径与Mg-RE-Zn合金（RE：稀土元素）的转变路径相似，但由于η′板之后析出的粗η′板的独特结构，导致析出相的组织演变与Mg-RE-Zn体系不同。时效100 h后，η相（Mg7Ca2Zn3）在基体中不均匀分布，最终演化为具有六边形结构的平衡η相（Mg10Ca3Zn6）。通过热力学第一性原理计算进一步确定了析出相的晶体结构和稳定性，支持了以下新的析出序列：ssssss→他区→η”→η”→η的双栈/η1→η
To obtain thorough understandings of precipitation process in heat-treatable Mg-Ca-Zn alloy, we revisited the precipitation process of a Mg-0.3Ca-0.6 Zn (at.%) dilute alloy during isothermal aging at 200 °C using an aberration-corrected scanning transmission electron microscope, atom probe tomography, and first-principles calculations. The monolayer G.P. zones form on the (0002)αplane in the peak-aged condition and transform into tri-atomic layerη''andη'plates with a thickness of a single unit-cell height. Theη'plates, then, form in pairs and stacks with energetically favorable 4–5 atomic layers of pure magnesium between the plates. While such a transformation path is similar to that seen in Mg-RE-Zn alloys (RE: rare-earth elements), the unique structure of coarseη1plates that precipitate after theη'plates leads to a different precipitate microstructure evolution from the Mg-RE-Zn system. Theη1phase (Mg7Ca2Zn3) is unevenly distributed in the matrix after 100 h of aging and finally evolves to the equilibriumηphase (Mg10Ca3Zn6) phase with a hexagonal structure. First-principles calculations of energetics were performed to further identify the crystal structure and stability of the precipitates, supporting the following new precipitation sequence:S.S.S.S. → G.P. zones →η'' → η' → η'pairs and stacks /η1→ η