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研究生(外文):Po-Wei Peng
論文名稱:Ni2CoCrFe與Ni2CoCrFeAl0.35 高熵合金的低溫相變化研究
論文名稱(外文):The study of low temperature phase transformations in Ni2CoCrFe and Ni2CoCrFeAl0.35 high entropy alloys
指導教授(外文):Wei-Chun Cheng
口試委員(外文):Wei-Chun ChengShyan-Kay JouShih-Hsun Chen
中文關鍵詞:高熵合金M23C6spinodal 相分離有序化相變化層狀反應L12相
外文關鍵詞:high entropy alloysM23C6spinodal decompositionordering reactionL12cellular reaction
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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.
第一章 前 言 1
第二章 文獻回顧 2
2.1高熵合金的相變化 2
2.2高熵合金析出物 6
第三章 實驗方法 19
3.1高熵合金熔鑄 19
3.2鑄錠加工 21
3.3熱處理 22
3.4分析儀器 22
3.5試片製備流程 29
第四章 結果與討論 40
4.1 Ni2CoCrFe相變化 41
4.2 Ni2CoCrFeAl0.35相變化 41
第五章 結論 62
參考文獻 65
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