利用田口式法則探討表面鋁化改質對Hastelloy X鎳基超合金在950℃下的高溫氧化行為

Study the Optimal Surface-aluminizing Coating by Taguchi Method to Enhance High–temperature Oxidation Behavior of a Ni-Based Superalloy (Hastelloy X)

本研究探討鎳基合金Hastelloy X （以下簡稱X合金）經田口式法進行不同參數下之改質合金（以下簡稱XA合金）在950℃空氣下的氧化行為。結果得知，最佳的滲鋁效應是選用12 %的NH4Cl，於氬流量200 cc/min、1000℃且持溫12小時的參數組合。這樣滲鋁改質的XA合金之氧化速率比X合金慢約2數量級，說明表面改質滲鋁能有效提升X合金之抗高溫氧化性能。經氧化後最佳參數滲鋁試片之氧化動力學呈現兩段式拋物線律。其中，氧化初期增重較大，而後期穩定階段的氧化數率大幅降低。整體而言，滲鋁改質合金的表面皆生成α與θ-Al2O3且隨著時間增長，θ-Al2O3的含量相對強度降低，而α-Al2O3則明顯增加。

The oxidation behavior of a nickel-based superalloy(Hastelloy X；named as the X alloy) after the surface aluminizing (XA) was investigated at 950 ℃in dry air. The optimal parameters of the aluminizing treatment obtained by the Taguchi method were to heat the alloy at 1000 oC for 12 hr in a 64 wt.% Al2O3-30 wt.% FeAl-6 wt.% NH4Cl mixture with an Ar-gas flow rate of 200 ml/min.
The oxidation kinetics of the optimal aluminized specimen followed a two-stage parabolic-rate law. The scales formed on the XA alloy consisted mostly of α-Al2O3 and minor amount of θ-Al2O3. The relative intensity of θ-Al2O3 under XRD analyses significantly decreased with increasing exposure duration, while that of α-Al2O3 went to an opposite direction.