添加不同元素之鈷鉻鐵鎳基五元高熵合金的高溫氧化行為

High Temperature Oxidation Behavior of Quinary CoCrFeNi-based High-entropy Alloys with Various Additonal Elements

本研究主要探討添加不同元素的三種鈷鉻鐵鎳基五元高熵合金，包含CoCrFeNiAl、CoCrFeNiSi及CoCrFeNiMn （以下分別簡稱H5A、H5S及H5M），在950℃的空氣氧化行為。研究結果顯示，三種合金的氧化動力學皆遵守拋物線律，其中五元添加Mn的合金氧化速率常數（kp值）遠大於其他合金；而五元添加Si或Al的合金kp值較低。由顯微結構分析得知，三種合金氧化後的氧化生成物皆不同，其中H5A只生成α-Al2O3及θ-Al2O3，H5S生成Cr2O3及SiO2；而H5M外層生成Mn3O4，內層生成(Mn,Cr)3O4及Cr2O3。推測SiO2及Al2O3的生成是含矽及鋁的五元高熵合金的氧化速率遠低於含錳五元高熵合金的主要原因。

The oxidation behavior of three CoCrFeNi-based high-entropy alloys containing CoCrFeNiAl (H5A), CoCrFeNiSi (H5S), and CoCrFeNiMn (H5M) was studied at 950 ℃ in dry air. In general, the oxidation kinetics of all the alloys followed the parabolic rate law, and the oxidation rate constants (kp values) of the alloys were strongly dependent on alloy composition. It was found that the Mn-additional alloy revealed the fastest oxidation rate, while the kp values of the Si- and Al-additional alloys were nearly identical. The scales formed on the H5A alloy consisted of α-Al2O3and θ-Al2O3, while Cr2O3 and SiO2 were detected on the H5S alloy. In addition, duplex scales fromed on the H5M alloy consisted on an outer-layer of mostly Mn3O4 and an inner-layer of (Mn,Cr)3O4 and Cr2O3. The formation of Al2O3 and SiO2 was responsible for the lower oxidation rates of Al- and Si-containing alloys with respect to that of the H5M alloy.