鎳基超合金及不銹鋼利用陰極電弧法被覆鎳鋁介金屬的抗熱循環氧化特性

Cyclic Oxidation Resistance of Ni-Al Deposited Nickel-Based Superalloy and Stainless Steel by Using Cathodic Arc Plasma Ion Plating

高溫絕熱塗層的發展過程中為了提昇抗高溫氧化特性，中介層的引入因應而生、並以熱熔射MCrAlY合金為主要典型。稍早本研究室利用離子輔助的陰極電弧法施鍍NiAl合金鍍膜在鋼材上，顯現極佳的抗熱循環氧化特性。故本研究持續使用該製程被覆NiAl鍍膜在鎳基超合金及不銹鋼上，並以更接近實際工作溫度的800℃及1100℃之熱循環氧化試驗，探討其抗循環氧化特性。利用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，輝光放電激發光譜分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；以Ni30Al70為靶材的鎳鋁介金屬可成功的被覆在鎳基超合金表面，形成Ni40Al60組成的初沉積鍍膜、其主相為Ni2Al3和NiAl3。熱循環氧化試驗顯示：鎳鋁鍍層可以有效的保護基材。在800℃熱循環試驗測試時，鎳鋁鍍膜生成NiAl結晶相，並且多餘的Al 擴散至基材，因而降低氧元素的擴散速率，達到保護底材的作用；而在較高溫的1100℃熱循環試驗測試下，除了NiAl鍍膜結晶相持續發揮功效外，更在鍍膜表面形成安定的α-Al2O3層，有效阻絕氧化現象的發生。

Thermal barrier coating (TBC) has been well developed to help protecting against high temperature oxidation, meanwhile applying an intermediate bond coat, typically of an MCrAlYtype metal alloy for further cyclic oxidation resistance enhancement. Previous study, demonstrating dramatical improvement on the cyclic oxidation resistance of steel using a novel process - cathodic arc ion plated NiAl, encourages this study to deposit NiAl on nickel-based alloy and stainless steel. Cyclic oxidation tests were carried out at 800℃ and 1100℃, higher than previous case, to approach the real service condition. Scanning electron microscopy (SEM) was used to observe surface morphology of the specimens. X-Ray diffractometry (XRD) was used to characterise the surface crystal structure using CuK radiation. A glow discharge optical emission spectrometer (GDOES) was used to analyse the composition and compositional depth profile of the specimens before and after cyclic oxidation tests. Experimental results show that Ni40Al60 film can be successfully deposited by using a Ni30Al70 target material. Ni2Al3 and NiAl3 are the major phases in the deposited film. When testing at 800 , the formation of 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 instead prevents from further oxidation.