金屬材料在超臨界水環境的腐蝕行為研究

Corrosion Behavior of Candidate Alloys used in Supercritical Water Environments

林玄侃(Hsuan-Kan Lin)

指導教授 ： 葉宗洸 ； 王美雅

國立清華大學/原子科學院/工程與系統科學系/碩士(2019年)

摘要

超臨界燃煤電廠與超臨界水反應器的運轉溫度和壓力高於水的臨界點 (374°C、22.1MPa)，因此有更高的熱轉換效率。然而，超臨界水具有可無限溶解 無極性氣體的特性，在此高運轉溫度下，使其水化學環境之腐蝕性相當嚴重。因 此，發展可適用於超臨界水高溫、高腐蝕性和高應力環境中的金屬材料，顯得相 當重要。
本論文選用四種合金，包括高熵合金 Al0.2Co1.5Cr1Fe1Ni1.5Ti0.3，肥粒麻田散 鐵 P92，奧斯田不鏽鋼 304H 和鎳基合金 Haynes 230，將四種合金試片置於溶氧 濃度為 8ppm、壓力 25MPa、550°C/ 650°C環境下進行腐蝕試驗，測試時間持續 至 1500 小時。腐蝕測試之後，測量其質量變化。後續透過掃描電子顯微鏡(SEM) 觀察樣品上氧化物的表面形態並同時使用X射線能量散布分析儀(EDX)分析氧 化物組成，再採用拉曼光譜儀判斷氧化物的晶體結構。在質量變化分析中，高熵 合金和 Haynes 230 在四種合金中表現出最佳的耐腐蝕性。 P92 和 304H 的表面 氧化物皆主要由 Fe3O4 和 Fe2O3 的外層和富含 Cr 的尖晶石氧化物的內層組成， 但前者緻密;後者發生嚴重氧化物剝落。另外通過製備 U-bend 試片測試在超臨 界水環境中的應力腐蝕龜裂(SCC)的敏感性。

關鍵字

超臨界水 ； 高熵合金 ； 應力腐蝕龜裂

並列摘要

As electricity consumption increases, the high efficiency and large capacity of ultra-supercritical(USC) instruments are widely used in the world. As the temperature of the steam cycles increases, the candidate materials must provide sustained corrosion resistance in the supercritical water environments. Several candidate alloys, including high-entropy alloys (Al0.2Co1.5Cr1Fe1Ni1.5Ti0.3), Ferritic–martensitic steels (P92), austenitic steel (304H), and Nickel-based alloy (Haynes 230), with high corrosion resistance and superior mechanical strength are potential materials for the structural components in SCW environments. Samples prepared from these alloys were exposed to a high-purity water environment with a dissolved oxygen concentration of 8 ppm. At pressure up to 25 MPa, corrosion tests were carried out at 550°C/650°C, and the test durations varied from 300 to 1500 hours. After the corrosion tests, the mass gain of each sample was measured using a high-precision electronic balance. The surface morphology of oxide on a sample was directly observed by scanning electron microscopy (SEM). The oxide composition was analyzed with energy-dispersive X-ray spectroscopy (EDX) and the crystal structure of the oxide was characterized by Raman Spectrometer. In mass gain analyses, the high-entropy alloys and Haynes 230 exhibited the best corrosion resistance among the four alloys. The surface oxides of P92 alloy mainly consisted of an outer layer of Fe3O4 and Fe2O3 and an inner layer of Cr-rich spinel oxide. The oxide spallation was observed on the surface of 304H sample for 300 hours corrosion test. Four alloys were also carried out in a supercritical water environment by U-bend test or creviced bend beam (CBB) test to examine their susceptibility to stress corrosion cracking (SCC). The morphologies of the samples surface were examined by SEM, and the quantitative analysis of the cracks on the surfaces of the samples were also carried out.

並列關鍵字

supercritical water ； high-entropy alloy ； stress corrosion cracking

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