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Please use this identifier to cite or link to this item: http://ntour.ntou.edu.tw:8080/ir/handle/987654321/52161

Title: Ni2FeCoCrAlX高熵超合金高溫氧化性質研究
High-Temperature Oxidation Properties of Ni2FeCoCrAlX High entropy Superalloys
Authors: Chien, Feng-Chih
簡逢志
Contributors: NTOU:Institute of Materials Engineering
國立臺灣海洋大學:材料工程研究所
Keywords: Ni2FeCoCrAlX高熵超合金;拋物線律;α-Al2O3;Cr2O3;(Fe,Cr)3O4;(Ni,Co)3O4;(Fe,Co)3O4;(Fe,Ni)3O4
Ni2FeCoCrAlX high-entropy superalloys;Parabolic-rate law;α-Al2O3;Cr2O3;(Fe,Cr)3O4;(Ni,Co)3O4;(Fe,Co)3O4;(Fe,Ni)3O4
Date: 2018
Issue Date: 2019-05-23T06:19:34Z
Abstract: 本研究分為三部分,第一部份探討添加不同含量的Al(含0、0.5、1及1.5 mole)對於Ni2FeCoCrAlX高熵超合金在700 ~ 900 ℃之空氣氧化行為,研究結果顯示,所有合金的氧化動力學皆遵守拋物線律,顯示固態擴散為合金氧化的主要機制;同時,所有超合金的氧化速率皆隨著溫度上升而增快,但隨鋁含量增加而降低。由顯微結構與XRD分析得知,未添加Al時,合金表面氧化物主要為FeCr2O4及NiCo2O4;而含鋁超合金表面之氧化物以Al2O3為主,其中,在700 ~ 800 oC時僅生成θ-Al2O3,而在900 oC時則為α-Al2O3,生成Al2O3是含Al高熵超合金氧化速率降低的主因;第二部份探Ni2FeCoCrAl0.5高熵超合金(簡稱N5-0.5Al)在900 ℃不同氧分壓(10-4 ~ 1 atm)下的氧化特性,研究結果得知,此超合金在900 ℃氧分壓10-4 ~ 0.21 atm下的氧化動力學亦遵守拋物線律,其氧化速率隨氧分壓上升而加快,但是在900 ℃純氧壓下卻發現有失重的現象,由顯微結構與XRD分析得知,在氧分壓10-4 ~ 0.21 atm下其氧化層生成單一的α-Al2O3層,且氧化層厚度隨著氧分壓增加而增厚,另外,在純氧壓下的氧化層有剝落的現象,透過分析得知氧化層生成α-Al2O3、Cr2O3與(Fe,Cr)3O4和(Ni,Co)3O4 的spinel混合氧化物;第三部份是在探討N5-0.5Al高熵超合金在700 ~ 900 ℃不同比例之CO/CO2混合氣之氧化行為研究,整體而言,該超合金在CO/CO2混合氣下,其氧化動力學亦遵守拋物線律,且氧化速率隨溫度上升而加快;另外,在900 ℃不同混合比(1CO/3CO2~1CO/30CO2)之氧化動力學皆遵守拋物線律,且其氧化動力學隨著CO2含量增加而加快。由顯微結構與XRD分析得知,在700 ~ 900 ℃不同比例CO/CO2混合氣的氧化反應下,高熵超合金皆會形成多種的氧化物,包含α-Al2O3、Cr2O3、(Fe,Co)3O4與(Fe,Ni)3O4的spinel混合氧化物,但無法形成完整的連續氧化層。
The main goal of this thesis is to investigate the high-temperature oxidation of four Ni2FeCoCrAlX high entropy superalloys (HESAs) in various oxygen-containing conditions. In the first part of the study, the oxidation behavior of Ni2FeCoCrAlX high-entropy superalloys (where X = 0, 0.5, 1.0 and 1.5) was studied over the temperature range of 700 ~ 900 oC in dry air. The oxidation kinetics of all the alloys followed the parabolic rate low, indicating that solid-state diffusion is the main controlling step of oxidation. The oxidation rates of all the alloys increased with increasing temperature, but decreased with increasing aluminum content. Based on microstructure and XRD analyses, the scales formed on the Al-free alloy consisted mostly of FeCr2O4 and NiCo2O4, while those of Al-containing alloys were composed of Al2O3. It was found that θ-Al2O3 formed on Al-containing alloys at 700-800 oC, while α-Al2O3 dominated at 900 oC. The formation of Al2O3 is responsible for the lower oxidation rates of Al-containing alloys. Secondly, the oxidation behavior of Ni2FeCoCrAl0.5(N5-0.5Al) was studied at various oxygen pressures from 10-4 to 1 atm at 900 °C. The oxidation kinetics of N5-0.5Al obeys the parabolic law at Po2 ≤ 0.21atm, having its oxidation rate increased with oxygen partial pressure. On the contrast, a mass-loss kinetics was observed at a pure oxygen pressure at 900 °C. The scale formed at Po2 ≤ 0.21atm consisted of an exclusine α-Al2O3 layer, having its thickness increased with oxygen partial pressure, while the oxide layer peeled off at a pure oxygen pressure. The scales formed at Po2 = 1atm were heterophasic, consisted of α-Al2O3, Cr2O3, (Fe,Cr)3O4, and (Ni,Co)3O4. Finally, the oxidation behavior of N5-0.5Al was studied at various ratios of CO/CO2 mixed gases at 700 - 900 °C. In general, the oxidation kinetics of the Ni2FeCoCrAl0.5 superalloy obeyed the parabolic law in all the gas mixture with its oxidation rate increased with increasing temperature and CO2 concentration. The scales formed on N5-0.5Al were also heterophasic, which were composed of intermixed α-Al2O3, Cr2O3, (Fe,Co)3O4, and (Fe,Ni)3O4 on top of the superalloy surface, and no continnous scale-layer was formed in any temperature and CO/CO2 gas mixture.
URI: http://ethesys.lib.ntou.edu.tw/cgi-bin/gs32/gsweb.cgi?o=dstdcdr&s=G0010555012.id
http://ntour.ntou.edu.tw:8080/ir/handle/987654321/52161
Appears in Collections:[材料工程研究所] 博碩士論文

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