電子束蒸鍍離子被覆鎳鋁介金屬的抗熱循環氧化特性

Cyclic Oxidation Resistance of Electron-Beam Evaporation Ion Plated Ni-Al Deposition

鎳鋁介金屬如所周知為一高溫材料，在先前嚐試陰極電弧離子被覆法製備鎳鋁鍍膜替代傳統MCrAlY中介層的研究中顯現高度的抗氧化特性。而利用電子束蒸鍍鎳鋁介金屬卻有著和PVD-YSZ的成熟技術結合成為單一階段製作絕熱塗層的利基，故本研究利用電子束蒸鍍離子被覆技術，以Ni30Al70、及Ni50Al50兩種成份的鎳鋁介金屬為蒸發源在不銹鋼及鎳基超合金上被覆鍍膜。利用熱循環氧化試驗探討其抗循環氧化特性，以掃描式電子顯微鏡觀察試片熱循環前後的表面形態，X-光繞射儀鑑定熱循環前後試片的氧化層晶體結構，輝光放電激發光析儀分析熱循環前後試片表面元素組成及其縱深分佈狀況。實驗結果顯示；鎳鋁鍍膜的元素及相組成受蒸發原料的影響極大。Ni30Al70為蒸發源所得鍍膜之初沉積結晶相為Al及少量的Ni2Al3；而Ni50Al50為蒸發源則為NiAl和Ni2Al3。雖然如此，熱循環氧化試驗顯示兩種組成的鎳鋁鍍層發生不同的保護機制，卻都可以有效保護基材。在800℃熱循環試驗時、兩種蒸發源所得鍍膜分別和不銹鋼及鎳基超合金基材發生擴散形成Fe3Al及NiAl結晶相，而得以降低氧元素的擴散。在較高溫的1100℃熱循環試驗下，除了Ni50Al50蒸發源本身所得的NiAl鍍層或因與基材相互擴散分別形成Fe3Al及Ni3Al 層持續發揮功能外，更都在鍍膜或化合層表面形成安定的α-Al2O3層，進一步阻絕氧化現象的發生。

NiAl intermetallic material has been subjected to high temperature applications. In previous study, an attempt has been made to improve the cyclic oxidation resistance of steel by using cathodic arc plasma ion plated NiAl, which seems possible to replace a conventional MCrAlY bond coat layer. Since electron-beam evaporation PVD-YSZ is well developed, to facilitate a single-stage thermal barrier coating process requires the combination of EBPVD-YSZ with EBPVD-bond coat, namely EBPVD-NiAl. Thus, Ni30Al70 and Ni50Al50 source materials were used to deposit NiAl films on stainless steel and nickel-base superalloy and to evaluate their cyclic oxidation resistance. Scanning electron microscope was used to observe surface morphology of the specimens. X-ray diffractometry was used to characterize surface phases using CuK α radiation. A glow discharge optical emission spectrometer was used to analyse the composition and compositional depth profile of the specimens before and after cyclic oxidation tests. Experimental results show that the deposited NiAl films are greatly influenced in composition and constituent phases by the evaporatant source material. Aluminum is the major phase with Ni2Al3 as minor phase were obtained by using Ni30Al70 as source material, while NiAl and Ni2Al3 were the major phases when using Ni50Al50 as source material. These two types of NiAl film can provide protection against high temperature oxidation during cyclic oxidation test, although mechanisms to resist high temperature are different. When testing at 800 , the formation of Fe3Al and NiAl phase is the primary contributor to thermal oxidation resistance due to low oxygen diffusivity in it, hence effectively protect substrate. On going to the higher test temperature 1100℃, the stable α-Al2O3 grown on the most top layer in addition to the Fe3Al or Ni3Al formation resulting form interdiffusion between coating and substrate instead prevents from further oxidation.