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Electrolytic Y2O3 and Al2O3 Coatings on IN617 Superalloy
|關鍵字:||Electrolytic deposition;電解沉積;Y2O3;YAG;Hot corrosion;High temperature oxidation.;氧化釔;釔鋁石榴石;熱腐蝕;高溫氧化||出版社:||材料工程學系||摘要:||
本研究以電解沉積法於IN617 超合金表面鍍上氧化釔(Y2O3)陶瓷塗層、氧化釔-氧化鋁(Y2O3/Al2O3))複合塗層，期提高基材之抗蝕性及抗高溫氧化能力。實驗結果顯示在-0.95 V ~ -2.5 V氫氧化釔之沉積反應為：
2(Y+3)(H2O)6 + 6e-®2Y(OH)3．3H2O + 3H2
藉由XRD, DSC ,TGA 進一步分析發現，熱處理過程中，於366℃吸附水與結晶水會完全失去。488℃則縮合成YOOH，最後於550℃轉化成Y2O3而且均勻附著在基材上。另一複合鍍層實驗結果發現熱處理過程中，於400℃吸附水與結晶水會完全失去，化學反應為：
Y(OH)3•3H2O →Y(OH)3 + 3 H2O
Al(OH)3•0.5H2O → Al(OH)3 + 0.5 H2O
3YOOH + 5AlOOH → Y3Al5O12 + 4H2O
再藉由sem觀察，相變化分析、高溫熱循環試驗、熱腐蝕試驗及電化學循環極化測試，此鍍膜均勻附著性佳。在常溫3.5% NaCl水溶液中、850℃ Na2SO4腐蝕環境中或1000℃高溫空氣中，氧化釔鍍層與氧化釔-氧化鋁複合塗層均比基材表現出較佳的抗蝕與抗高溫氧化能力。唯於鹽酸(HCl) 水溶液中，只有複合鍍層具有抵抗能力，因為氧化釔會溶於鹽酸(HCl)水溶液。
The mechanism of electrolytic yttrium hydroxide thin film deposition on IN617 superalloy in Y(NO3)3 aqueous solution were investigated. The cathodic polarization curve in Y(NO3)3 aqueous solution can be divided into two portions: 1. the reduction of H+ and O2, 2. the reduction of (Y+3)(H2O)6 i.e.
2(Y+3)(H2O)6 + 6e-2Y(OH)3．3H2O + 3H2
at -0.95 V ~ -2.5 V. it was found that the as-coated film was hydrated Y(OH)3．3H2O, dehydrated into Y(OH)3．H2O at 122℃, further dehydrated into Y(OH)3 at 366℃, condensed into YOOH at 480℃, and finally transformed into Y2O3 at 550℃. Also, a novel method of electrochemical synthesis of YAG (yttrium aluminum garnet) thin film coating on IN617 has been successfully developed. The coating film was composed of hydrated Y(OH)3•3H2O and Al(OH)3•0.5H2O, the physical adsorbed water evaporated between 25 and 103℃, dehydrated into Y(OH)3 and Al(OH)3 between 103 and 400℃, condensed into YOOH and AlOOH between 400 and 850℃, and finally transformed into single phase YAG (Y3Al5O12) between 850 and 1000℃ by the reaction,
3YOOH + 5AlOOH Y3Al5O12 + 4H2O
Thermal cycle tests, hot corrosion in Na2SO4, and corrosion in HCl aqueous solutions of the IN617 substrate, Y2O3 coated, Y2O3/Al2O3 double layers coated and YAG coated are further conducted to investigate the high temperature oxidation and corrosion. It was found that the Y2O3 coating and the composite coating could improve significantly the resistance of thermal cycle oxidation, hot corrosion in Na2SO4. The Y2O3 and Y2O3/Al2O3 composite coated specimens revealed only a small amount of weight variation because of the formation of protective films, such as Y2O3, Y2O3/Al2O3 and YAG. The composite coated specimen also revealed excellent corrosion resistance in HCl aqueous solution. However, the Y2O3 coated specimen revealed more weight loss than the uncoated in HCl aqueous solution, since the dissolution of Y2O3 coatings resulted in the exposure of the substrate.
|Appears in Collections:||材料科學與工程學系|
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