研究生: |
彭柏瑋 Po-Wei Peng |
---|---|
論文名稱: |
Ni2CoCrFe與Ni2CoCrFeAl0.35 高熵合金的低溫相變化研究 The study of low temperature phase transformations in Ni2CoCrFe and Ni2CoCrFeAl0.35 high entropy alloys |
指導教授: |
鄭偉鈞
Wei-Chun Cheng |
口試委員: |
鄭偉鈞
Wei-Chun Cheng 周賢鎧 Shyan-Kay Jou 陳士勛 Shih-Hsun Chen |
學位類別: |
碩士 Master |
系所名稱: |
工程學院 - 機械工程系 Department of Mechanical Engineering |
論文出版年: | 2020 |
畢業學年度: | 108 |
語文別: | 中文 |
論文頁數: | 68 |
中文關鍵詞: | 高熵合金 、M23C6 、spinodal 相分離 、有序化相變化 、層狀反應 、L12相 |
外文關鍵詞: | high entropy alloys, M23C6, spinodal decomposition, ordering reaction, L12, cellular reaction |
相關次數: | 點閱:184 下載:0 |
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高熵合金是由多種溶質元素且無主要溶劑元素所組成的合金,突破傳統以單一元素為主的傳統合金設計方法,而高熵合金經由適當的設計與熱處理,可獲得良好的機械與物理性質,例如:高熵合金具有高硬度、高溫強度、抗腐蝕與抗氧化等性質。本論文探討由真空熔煉的合金A(Ni2CoCrFe)和合金B(Ni2CoCrFeAl0.35)高熵合金,觀察其經固溶處理與低溫恆溫處理後的微觀結構改變和機械性質變化:合金A經低溫恆溫處理後硬度無明顯變化而合金B有明顯發生變化。以X光繞射得知合金A與和金B相結構經固溶處理與低溫長時間恆溫處理後均由單相的沃斯田體(r)所組成。發現合金A與合金B合金經長時間恆溫處理後有M23C6晶界析出物的產生。而合金B經熱處理後發生spinodal相分離與有序化反應。冷卻過程發生spinodal相分離與有序化相變化。其中沃斯田體相的相變化形式如下:高溫沃斯田體於冷卻過程中分解為二個低溫沃斯田體(r′ + r′′),而高濃度的′′相於更低溫時,經由有序化反應而相轉變為L12相。其總反應式為:r-> r ’ + r” -> r’ + + L12,於低溫時合金B的晶界處有層狀組織生成。
High-entropy alloys (HEAs) are new kinds of alloys different from the traditional alloys which composed of at least five principal elements. This feature introduces that HEAs would have some properties, such as excellent mechanical properties, high temperature strength and corrosion resistance. However, the development and design of the HEAs require knowledge of the phase transformations that occur during the alloy making processes and heat treatments. The present study is a continuation of the previous work and aims to understand the microstructure and phase transformations of the alloys, Alloy A (Ni2CoCrFe) and Alloy B (Ni2CoCrFeAl0.35) after solution treatment for 1 hour and then quenched followed by prolonged annealing for 100 hours isothermally at various temperature. The results of our study show that there are M23C6 grain boundary precipitation in Ni2CoCrFe and Ni2CoCrFeAl0.35 after prolong annealing for 100 hours at various studied temperature. The results of our study show that the spinodal decompositions occur in CoCrFeNiAl0.35 alloys after heating and cooling from 1050℃, the high temperature austenite (r) decomposes into low temperature solute-lean austenite (r’) and solute-enriched austenite (r”). The solute-enriched austenite phase also transforms into L12 phase via the ordering reaction upon cooling to lower temperature. The occurrence of spinodal decomposition and ordering reaction in the austenite phase of the Alloy B can be written as follows:
r-> r ’ + r” -> r’ + L12. Coherent fine particles of L12-type precipitates homogeneously in the austenite matrix in alloy B. In addition, cellular reaction also occurs and lamellae of austenite grow from the grain boundary.
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