海歸學者發起的公益學術平臺
分享資訊，整合資源
交流學術，偶爾風月
單晶矽是目前晶片領域應用最廣泛的材料，由於其脆性本質，其加工難度一直居高不下。因此對單晶矽塑性變形的研究一直是廣大科研工作者的追求。然而，由於單晶矽的變形機理不僅包括傳統的位錯變形，還包括馬氏體相變及非晶化相變過程，具有多尺度-多機理的變形特徵，不論實驗還是模擬都具有極高的難度。
來自江蘇大學機械學院的陳浩老師和美國愛荷華州立大學航空航天工程系的Valery I. Levitas教授，針對單晶矽極端剪下載荷下的非晶剪下帶形成機理，採用了理論-計算耦合方法，提出了一種矽內部區域性流動產生的新理論，揭示了晶體材料內部區域性流動產生的物理本質來源於晶體內光學聲子的失穩條件，並確定了非晶矽內部流動的微觀轉變過程。
Fig. 1 | Pressure-temperature phase diagram for Si under hydrostatic loading.
Fig. 2 | High-resolution transmission electron microscopy images of strain-induced amorphous bands in Si I.
Fig. 3 | Stress and strain fields in Si during shear.
他們採用分子動力學研究了單晶矽的剪下變形，發現單晶矽的剪下失穩來源於光學聲子失穩，並在失穩後發生了局部流動。透過計算流動中材料的剪下粘滯係數，確定了流動中材料發生了熔化而不是非晶化。透過熱力學第二定律，確定了單晶矽內部發生區域性熔化所需的外載入荷條件。該研究除了發現了單晶矽內部區域性熔化變形機理外，還確定了單晶矽剪下帶內部變形機理，發現了非晶態矽↔矽I、非晶態矽↔矽IV和矽I↔矽IV之間的迴圈轉變。所有相的體積分數大多在0.2至0.4之間，且奈米結構演化具有不可重複性。這種迴圈轉變透過體積變化產生的轉變應變和轉變誘導塑性產生了額外的塑性變形重要載體，這種轉變可能發生在各種材料系統的剪下帶中，但在實驗和模擬中常被忽略。剪下應力的釋放使微觀結構淬火，並與現有實驗表現出合理的定性一致性。
該研究提供了一種新的單晶矽非晶帶形成機理，在一定程度上解釋了單晶矽極端載荷下的微觀變形機理。該文近期發表於npj Computational Materials11,：59 (2025)，英文標題與摘要如下，點選左下角“閱讀原文”可以自由獲取論文PDF。
Virtual melting and cyclic transformations between amorphous Si, Si I, and Si IV in a shear band at room temperature
Hao Chen & Valery I. Levitas
Virtual melting (VM) as alternative deformation and stress relaxation mechanisms under extreme load is directly validated by molecular dynamics (MD) simulations of the simple shear of single crystal Si I at a temperature 1383 K below the melting temperature. The shear band consisting of liquid Si is formed immediately after the shear instability while stresses drop to zero. This process is independent of the applied shear rate. A new thermodynamic approach is developed, and the thermodynamic criterion for VM, which depends on the ratio of the sample to shear band widths, is derived analytically and confirmed by MD simulations. Since stress-free melt is unstable at 300 K, with further shear, the VM immediately transforms to a mixture of low-density amorphous a-Si, stable Si I, and metastable Si IV. Cyclic transformations between a-Si ↔ Si I, a-Si ↔ Si IV, and Si I ↔ Si IV with volume fraction of all phases mostly between 0.2 and 0.4 and non-repeatable nanostructure evolution are reveled. Such cyclic transformations produce additional important carriers for plastic deformation through transformation strain and transformation-induced plasticity due to volume change, which may occur in shear bands in various material systems but missed in experiments and simulations. The release of shear stresses quenches the microstructure, and shows reasonable qualitative correspondence with existing experiments.
擴充套件閱讀
媒體轉載聯絡授權請看下方