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標題: | 界面析出碳化物和差排在單晶肥粒鐵奈米柱中交互作用之研究 The Interaction between the Interphase-precipitated Carbides and Dislocations in Single Crystal α-ferrite Nanopillars |
作者: | Ming-Yuan Gao 高銘遠 |
指導教授: | 楊哲人(Jer-Ren Yang) |
關鍵字: | 界面析出碳化物,差排,肥粒鐵,同步觀測壓縮試驗,穿透式電子顯微鏡,奈米壓痕, interphase-precipitated carbide,dislocation,α-ferrite,in-situ compression,transmission electron microscopy (TEM),nanoindentation, |
出版年 : | 2018 |
學位: | 碩士 |
摘要: | 界面析出物碳化物於沃斯田鐵至肥粒鐵相變過程中成核,這種奈米級析出物藉由與差排的交互作用給予肥粒鐵相當大的強化效果,本論文目的在於透過合金與熱處理的設計、輔以穿透式電子顯微鏡同步觀測的壓縮試驗、奈米壓痕的技術,來釐清界面析出碳化物與差排間的交互作用和界面析出物在肥粒鐵內的析出行為。
在輔以穿透式電子顯微鏡同步觀測的壓縮試驗中,研究界面析出物強化肥粒鐵奈米柱之變形行為。藉由聚焦離子束來製備三種肥粒鐵單晶奈米柱: 不含界面析出物之肥粒鐵奈米柱、含有較小且較密界面析出物之肥粒鐵奈米柱以及含有較大但較疏界面析出物之肥粒鐵奈米柱。實驗結果指出三種奈米柱的應力應變曲線中皆含有小型與中型的應變爆發,大型的應變爆發只發生於不含界面析出物之奈米柱,而應變爆發的產生與不同的差排行為有關,例如﹕差排的成核、滑移、增生和消弭。另外,透過同步觀測試驗發現含有界面析出物之奈米柱,其奈米級析出物限制住差排的滑移,導致應變爆發的量下降,並伴隨奈米柱強度的上升。相對地,在不含界面析出物之奈米柱中,由於沒有析出物可以阻擋差排的滑移,導致有明顯機械退火(透過施加的應力,造成奈米柱內差排密度顯著下降)之現象、較大的應變爆發以及較低的奈米柱強度。 此外,肥力鐵成長次序對界面析出碳化物之析出行為的影響則透過奈米壓痕來進行探討,實驗結果揭示含有界面析出物之肥粒鐵因界面析出物的貢獻,相較於不含界面析出物之肥粒鐵有較大的硬度和標準差。在不含界面析出物的肥粒鐵中,其奈硬度不隨肥粒鐵成長次序改變。然而,界面析出物強化肥粒鐵隨肥粒鐵成長次序的奈硬度則呈現先下降而後上升的現象,可能原因來自肥粒鐵成長隨不同沃斯田鐵至肥粒鐵相變階段改變,導致在單一肥粒鐵內界面析出碳化物陣列間距的不同,進而造成硬度上的變化。 Interphase-precipitated carbides form during the austenite-to-ferrite transformation, and it is believed to give enormous strengthening contribution to ferrite matrix by interaction with dislocations. The present work aims to clarify the interaction between interphase-precipitated carbides and dislocations, and the precipitated behavior of interphase precipitation in ferrite through in-situ transmission electron microscopy compression tests and the techniques of nanoindentation coupled with the alloy and the heat treatment designs. Compressive deformation tests were carried out in in-situ transmission electron microscopy to investigate the deformation behaviors of interphase-precipitated-carbide strengthened α-iron nanopillars. Three kinds of α-iron single-crystal nanopillars were prepared by focused ion beam: interphase-precipitated-carbide-free pillars and two types of interphase-precipitated-carbide-bearing pillars with carbides of different sizes and densities. The results indicated that the plastic flows for all the specimens consist of small and intermediate strain bursts, while large strain bursts only occur in interphase-precipitated-carbide-free pillars. The strain bursts were associated with different dislocation behaviors (e.g. dislocation nucleation, movement, multiplication, and annihilation). Furthermore, in-situ observation provided the direct evidences that interphase-precipitated carbides in the pillars confined the movement of the dislocations, resulting in smaller strain bursts with a significant higher strength of pillars. In contrast, pillars without carbides showed prominent mechanical annealing (i.e., a significant drop in stored dislocation density in response to applied stress), larger strain burst and a lower strength of pillars. Moreover, the effect of the ferrite transformation sequence on the precipitated behavior of interphase-precipitated carbides in ferrite has been investigated through nanoindentation tests. The results revealed that higher hardness and deviation for interphase precipitation-bearing ferrite, which was associated with interphase precipitation. In addition, the nanohardness for interphase precipitation-free ferrite did not vary much with the ferrite transformation sequence; however, the nanohardness of interphase precipitation-bearing ferrite (as a function of the ferrite transformation sequence) firstly decreased, and then subsequently increased; it possibly suggested that the growth of ferrite varied with the stages of austenite to ferrite transformation, leading to different sheet spacings in a single ferrite. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/77794 |
DOI: | 10.6342/NTU201801500 |
全文授權: | 有償授權 |
電子全文公開日期: | 2023-08-13 |
顯示於系所單位: | 材料科學與工程學系 |
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