Developing a Mg Alloy with Ultrahigh Room Temperature Ductility via Grain Boundary Segregation and Activation of Non-basal Slips
Developing a Mg Alloy with Ultrahigh Room Temperature Ductility via Grain Boundary Segregation and Activation of Non-basal Slips
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DOI：
10.1016/j.ijplas.2023.103548
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发表时间：
2023-01
影响因子：
9.8
通讯作者：
Zhi Zhang;Jinghuai Zhang;Jin-shu Xie;Shujuan Liu;W. Fu;R. Wu
中科院分区：
文献类型：
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作者：
Zhi Zhang;Jinghuai Zhang;Jin-shu Xie;Shujuan Liu;W. Fu;R. Wu
镁合金的室温塑性差是其固有的缺点，这限制了其广泛应用。晶粒细化是同时提高塑性和强度的公认方法。然而，获得超细晶粒（约1 μm及以下）通常需要剧烈的变形工艺，不利于广泛应用。在这里，通过利用独特的设计策略，即，引入有益溶质，实现晶界（GB）偏聚，有效降低非基面滑移与基面滑移的临界分辨剪切应力（CRSS）比，从而有效激活非基面滑移，获得了中细晶粒（≤ 8 μm）的Mg-0.3Er（at%）合金，室温延伸率接近50%。散射衍射和滑移线分析以及弱束暗场观察证实，微量Er元素和适当的细晶粒有助于激活大量的非基底位错和抑制孪晶。此外，通过能谱元素分析进行系统研究，发现300 °C退火的合金的GB偏析水平高于360 °C退火的合金。较高的晶界偏析水平会影响合金的内聚强度，并有利于激活更多的非基面位错来调节局部应力，从而抑制晶界开裂，最终提高合金的塑性。该研究不仅为大规模开发室温高塑性镁合金提供了一条有效途径，而且通过揭示非基面滑移的比例和GB偏析的水平，为阐明高温塑性的起源提供了新的见解。
Poor room temperature (RT) ductility is an inherent disadvantage of magnesium (Mg) alloys, which limits their wide application. Grain refinement is an accepted method to improve ductility and strength simultaneously. However, obtaining ultrafine grains (about 1 μm and below) usually requires severe deformation processes, which is not conducive to be widely used. Here, by utilizing a distinctive design strategy, i.e., introducing beneficial solute to achieve grain boundary (GB) segregation and effectively reduce the critical resolved shear stress (CRSS) ratio between non-basal slips and basal slip, thus efficiently activating non-basal slips, we obtained a Mg-0.3Er (at%) alloy with moderate-fine grains (∼8 μm) having elongation near 50% at RT. Based on the results of in-situ electron back-scatter diffraction and slip trace analysis, and weak beam dark-field observation, we confirmed that minor Er element and appropriate fine grains would contribute to the activation of considerable non-basal dislocations and the suppression of twinning. In addition, through energy dispersive spectrometry element analyses for systematic investigation, we found that the GB segregation level of the alloy annealed at 300 °C is higher than that of the alloy annealed at 360 °C. The higher GB segregation level would impact the cohesion strength and be conducive to activate more non-basal dislocations to accommodate local stress, thus suppressing the GB cracking and finally improving the ductility. This study not only suggests an effective way for large-scale development of high ductility Mg alloys at RT, but also provides a new insight to elucidate the origins of ultrahigh ductility by revealing the fraction of non-basal slips and the level of GB segregation.