臨場變形穿透式電子顯微鏡研究CoCrNiSi_(0.15)中熵合金之慢速壓縮與壓縮後拉伸之變形行為演變
Other Title
Deformation Behavior Observation of Slow Compression and Tensile After Compression in A CoCrNiSi_(0.15) Medium Entropy Alloy Via In-situ Deformation Transmission Electron Microscope
Journal
鑛冶：中國鑛冶工程學會會刊
Journal Volume
68
Journal Issue
3
Start Page
52
End Page
58
ISSN
0451-0011
Date Issued
2024-09
Author(s)
戴正凌
Abstract
CoCrNi中熵合金由於雙晶變形機制，於低溫下有極高之強度與延展性。然而其重量過重及於室溫下強度略顯不足。藉由添加矽除了達到輕量化之目的外，也有固溶強化效果及降低疊差（stack fault energy）能之功用。此外，先將特定材料進行一定程度壓縮後，也有助於提升後續拉伸強度。本研究於臨場變形穿透式電子顯微鏡（in-situ deformation TEM）中使用奈米壓針對奈米柱進行變形，研究輕量化CoCrNiSi_(0.15)中熵合金慢速壓縮與壓縮後拉伸之變形行為演變。此處以雙光束（two-beam）條件，g=[110]方向下進行觀察，可使顯示之差排減半，避免過多差排導致觀測不易。研究結果顯示CoCrNiSi_(0.15)慢速壓縮變形下，於變形初期即以疊差（stacking fault）及差排（dislocation）進行變形，後續變形可觀察到少量變形雙晶形成，阻礙差排滑移。隨後進行慢速拉伸實驗，僅微量變形即可明顯看到大量變形雙晶形成，顯示出預先壓縮至形成變形雙晶後再進行拉伸能更快速達到此材料之臨界雙晶剪應力，以獲得更高強度之材料。本研究以直接證據證實了於輕量化CoCrNiSi_(0.15)中熵合金中慢速壓縮後拉伸之顯微結構變形機制演變，彌補了模擬計算及塊材變形無直接證據之缺陷。
CoCrNi medium-entropy alloys exhibit exceptional strength and ductility at low temperatures due to the formation of deformation twins. However, their strength at room temperature remains insufficient. The addition of Si serves the dual purpose of achieving light-weighting and enhancing solid solution strengthening while reducing stack fault energy. Additionally, controlled compression of specific materials can further enhance subsequent tensile strength. This study investigates the deformation behavior of a lightweight CoCrNiSi_(0.15) medium-entropy alloy through in-situ deformation transmission electron microscopy (in-situ deformation TEM), utilizing nano-indentation for slow compression and subsequent tensile testing of nano-pillars. Observations are conducted under a two-beam condition with the g = [110] direction to minimize displayed dislocations by half and alleviate issues associated with excessive dislocation hindering observation. Results indicate that, during slow compression deformation of CoCrNiSi_(0.15), stacking faults and dislocations form in the early stages, with a subsequent formation of a small number of deformation twins, impeding dislocation movement. In subsequent tensile experiments, a significant number of deformation twins are observed. This suggests that pre-compression to induce deformation twins, followed by a tensile test, expedites the attainment of critical shear stress for deformation twins, leading to a material with higher strength. This study provides direct evidence of the microstructural deformation mechanism in a CoCrNiSi_(0.15) medium-entropy alloy for lightweight applications. The approach of slow compression followed by tensile testing complements simulation calculations, addressing their limitation of lacking direct evidence of deformation behavior.
Subjects
CoCrNi中熵合金
輕量化矽添加
臨場變形穿透式電子顯微鏡
變形雙晶
慢速壓縮後拉伸
CoCrNi medium entropy alloy
Si addition
In-situ deformation transmission electron microscope
Deformation twin
Tensile after compression
Type
journal article