以原子層沉積技術提升鋁基碳化矽複合材料之抗腐蝕性

Improvement of Corrosion Resistance of Aluminum Matrix Composites by Atomic Layer Deposition

陳映竹(Ying-Chu Chen)

指導教授 ： 林新智

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2022年)

https://doi.org/10.6342/NTU202202973

摘要

鋁基複合材料(AMC)泛指以鋁合金作為基底而製成的複合材料。其中，陶瓷材料如碳化矽顆粒常被作為AMC的添加相，以製備出具有可調節(tailorable)性能的材料。近十年，關於AMC的文獻數量逐年攀升，AMC也被應用在許多場合當中。有文獻指出，AMC的腐蝕速率比鋁合金高，且孔蝕也是一大隱憂。然而，目前關於AMC腐蝕保護的文獻並不多，也尚未找到適合且有效的腐蝕保護方法。本研究利用原子層沉積(ALD)技術，沉積氧化鉿(HfO2)、氧化鋯(ZrO2)、氧化鈦(TiO2)以及氧化鋁(Al2O3)薄膜於鋁基碳化矽顆粒複合材料上。利用穿透式電子顯微鏡觀察薄膜在AMC上的形貌及均勻性，再以動電位極化法及交流阻抗譜，分析四種薄膜對於AMC在1.5%氯化鈉水溶液中的腐蝕保護性。結果顯示四種薄膜皆有效使得腐蝕電流密度下降，其中以氧化鉿的效果最為顯著。本研究也利用ALD技術沉積了50、100、150及200個循環的氧化鉿薄膜，以探討薄膜的厚度效應。腐蝕電流及阻抗頻譜的結果顯示，氧化鉿薄膜的腐蝕保護性大致上隨著厚度上升而提高，但是呈現趨近飽和的趨勢。這暗示不需要再將厚度提升就能達到十分優異的腐蝕保護性，以減少金錢及時間成本的耗費。
為了探究腐蝕形貌的變化，我們將AMC裸材以及有氧化鉿薄膜保護的AMC (HfO2/AMC) 放入1.5%氯化鈉水溶液中浸泡4小時及8小時後取出，觀察二次電子影像以及元素分布圖。結果顯示浸泡8小時的AMC裸材上出現蝕孔，而HfO2/AMC上產生裂紋。AMC裸材上的蝕孔分布範圍小且深，HfO2/AMC的裂紋則是廣而淺，顯示HfO2薄膜有效降低孔蝕的嚴重程度或延後孔蝕的發生。
本研究是第一個將ALD技術應用於AMC腐蝕保護上的研究。研究成果顯示ALD薄膜能均勻地沉積在AMC上，並且對AMC的抗腐蝕性有非常顯著的提升，以及減緩孔蝕的發生。

關鍵字

原子層沉積 ； 腐蝕保護 ； 鋁基複合材料 ； 極化曲線 ； 交流阻抗譜

並列摘要

Aluminum matrix composites (AMCs) have been used in various applications and the number of journal articles regarding AMCs has been rising yearly. It has been reported that AMCs reinforced with silicon carbide (SiC) particles have a higher corrosion rate than aluminum alloys and are prone to pitting corrosion. However, there has been little study on the corrosion protection of AMCs, and no effective method has been proposed yet. In this work, we revealed that atomic layer deposition (ALD) is a feasible method to provide corrosion protection to AMCs reinforced with SiC particles. Thin films of HfO2, ZrO2, TiO2, and Al2O3 were deposited using ALD on AMC reinforced with 20 vol.% SiC particles. Observation of transmission electron microscope (TEM) images showed that these thin films were grown on AMC well and uniformly. Their corrosion protection properties were measured using potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS). Analysis showed that HfO2, ZrO2, TiO2, and Al2O3 thin films of 200 cycles provided enhanced corrosion protection to AMC from 1.5% NaCl (aq) solution, with HfO2 providing the highest level of protection. The effect of film thickness on corrosion protection properties was also investigated using AMC covered with HfO2 films of 50, 100, 150, and 200 cycles. Analysis of current density and impedance revealed that corrosion resistance generally increased with increasing film thickness but showed a sign of saturation, indicating that a further increase in film thickness will be unnecessary.
To investigate the differences between the corrosion behavior of bare AMC and thin film-protected AMC, bare AMC and AMC covered with HfO2 films of 200 cycles (HfO2/AMC) were immersed in 1.5% NaCl (aq) solution for 4 and 8 hours. After immersion, their corrosion morphologies and corrosion products were compared and contrasted. Scanning electron microscope (SEM) images and elemental mappings from electron probe microanalyzer (EPMA) showed that corrosion pits were found on bare AMC after 8 hours of immersion but only cracks were observed on HfO2/AMC. The corrosion pits on bare AMC were local and deep, while the corrosion cracks on HfO2/AMC propagated outwardly and appeared in a much larger region. This indicates that HfO2 films can lessen the severity or delay the occurrence of pitting corrosion.
This is the first reported instance of using oxide thin films fabricated by ALD for the corrosion protection of aluminum matrix composites. We reported improved corrosion resistance and showed the differences in corrosion morphologies between bare AMC and AMC covered with HfO2 thin films.

並列關鍵字

atomic layer deposition ； corrosion protection ； aluminum matrix composites ； potentiodynamic polarization ； electrochemical impedance spectroscopy

參考文獻

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