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Please use this identifier to cite or link to this item: http://ntour.ntou.edu.tw:8080/ir/handle/987654321/52160

Title: FeCoNiCr基高熵合金於不同含氧環境下氧化行為研究
High-temperature Oxidation Behavior
Authors: Wang, Ting-En
王廷恩
Contributors: NTOU:Institute of Materials Engineering
國立臺灣海洋大學:材料工程研究所
Keywords: 高熵合金;氧化;水汽;超臨界水
high-entropy alloy;oxidation;water vapor;supercritical water
Date: 2018
Issue Date: 2019-05-23T06:19:33Z
Abstract: 本研究探討FeCoNiCr (H4)、FeCoNiCrAl (H5A)、FeCoNiCrMn (H5M)及FeCoNiCrSi (H5S)四種等莫耳高熵合金在650°C空氣與空氣含水汽(90%空氣含10%水汽與50%空氣含50%水汽兩種比例)以及超臨界水環境下(溫度為650 oC; PH2O(g)為25 MPa)的氧化行為。研究結果顯示,在乾空氣環境下,四種合金的氧化動力學皆遵守拋物線律,且它們的氧化速率由快至慢之順序分別為H5M > H4 > H5A > H5S;XRD分析得知,H4合金生成單一Cr2O3層,H5A合金生成θ-Al2O3,H5M合金生成兩層氧化層,其中,內層主要是MnCr2O4,而外層則是Mn2O3,而H5S合金僅生成薄且連續的Cr2O3及SiO2之混和氧化層。而在含10%及50%水汽氧化時,四種等莫耳高熵合金的氧化生成物與空氣相似,但H4與H5S合金的氧化動力學呈現先增重後失重的情況,顯示氧化物有剝落情況產生。而H5A及H5M合金的氧化動力學則遵守增重式拋物線律,且氧化速率常數(kp值)隨水汽的含量增加而加快。最後,在超臨界水環境下, H4、H5M及H5S合金的氧化動力學則遵守增重式拋物線律,三種合金的氧化速率由快至慢之順序分別為H5S > H5M >H4;其中,H4合金在氧化後,生成兩層的氧化物,內層主要生成Cr2O3、FeCr2O4及NiCr2O4,而外層則是生成Fe3O4及CoCr2O4;同時, H5M合金在氧化後和空氣氧化相似,亦生成兩層氧化層,內層主要生成MnCr2O4,而外層則是Mn2O3;反之,H5A合金呈現先增重後嚴重失重的情況,而H5S合金在超臨界環境初期的氧化速率比空氣下快了4.5個數量級,且在200小時後出現失重反應,該合金在超臨界環境氧化後則形成兩層氧化層,包括內層仍為Cr2O3及SiO2混合層,而外層則以FeCr2O4為主,並有少量的Fe2SiO4生成。
This thesis is to study the oxidation behaviors of FeCoNiCr-based high-entropy alloys, containing FeMoNiCr (H4), FeCoNiCrAl (H5A), FeCoNiCrMn (H5M) and FeCoNiCrSi (H5S) at 650°C in dry/wet air (with 10% and 50% H2O(g)) and in supercritical-water environment (at PH2O(g) = 25 MPa). The results generally showed that the oxidation kinetics of all the alloys in dry air obeyed the parabolic-rate law, with the oxidation rate followed by the fast to slow rank of H5M > H4 > H5A > H5S. An exclusive scale of Cr2O3 and θ-Al2O3 formed on H4 and H5A, respectively, while duplex scales formed on H5M. Those of H5M consisted of an outer layer of Mn2O3 and an inner layer of MnCr2O4. In addition, an intermixed layer of Cr2O3 and SiO2 formed on H5S. The scale constitution and phases formed in wet air were similar to those in dry air, however the oxidation behavior of H4 and H5S underwent an initial mass-gain, but followed by a mass-loss kinetics. On the contrast, the wet-air oxidation of H5A and H5M experienced the mass-gain kinetics, having their oxidation rate constants (kp values) increasing with water-vapor content. In addition, the oxidation kinetics of the alloys in supercritical water environment also obeyed the parabolic-rate law, with their oxidation rate followed by the fast to slow rank of H5S > H5M > H4, while severe mass-loss kinetics was obeyed for H5A. Duplex scales formed on H4 in supercritical water environment, consisted of an outer layer of Fe3O4 and CoCr2O4, an inner layer of Cr2O3, FeCr2O4 and NiCr2O4. The scales formed on H5M and H5A are similar to those in dry air, while those on H5S consisted of an outer layer of FeCr2O4 and Fe2SiO4 and, an inner layer of Cr2O3 and SiO2. In general, the oxidation rate of H5S in supercritical water environment is about 4.5 orders of mafnitale faster than that in dry and the mass-lose kinetics was noted at 650oC after a 200-h exposure.
URI: http://ethesys.lib.ntou.edu.tw/cgi-bin/gs32/gsweb.cgi?o=dstdcdr&s=G0010555015.id
http://ntour.ntou.edu.tw:8080/ir/handle/987654321/52160
Appears in Collections:[材料工程研究所] 博碩士論文

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