微米級Ti(C, N)對A286超合金腐蝕行為之影響

Abstract

A286超合金是一種具有優異抗蝕性及高溫強度的材料，被廣泛應用於航空航天和能源領域。本研究主要探討Ti(C, N)二次相對A286超合金的腐蝕行為之影響，並以動電位極化曲線、循環動電位極化曲線等電化學方法進行分析。本研究採用兩種不同熱處理方式處理A286超合金，並選取316L不鏽鋼作為對照組。透過光學顯微鏡(OM)和掃描電子顯微鏡(SEM)觀察材料表面微結構變化，並利用穿透式電子顯微鏡(TEM)和能量散射X射線譜(EDS)分析介在物的化學組成。 研究結果顯示，A286合金中晶出物主要為Ti(C, N)，其多在熔湯冷卻時以CaO、MgO、CaS等介在物為核心形成。這些Ti(C, N)晶出物在孔蝕過程中扮演著重要角色，A286合金上的孔蝕多由Ti(C, N)晶出物開始，與固溶後形成的析出物無關。電化學測試結果顯示，相較於316L不鏽鋼，A286合金在電渣重溶(ESR)後具有極低的硫含量，因此孔蝕多由氧化物引發，且大多數孔蝕會再鈍化，只有極少數能成長到穩態階段。具體而言，孔蝕可分為三個階段：第一階段，CaO優先溶解，形成約1-2微米的圓形蝕孔；第二階段，Ti(C, N)晶出物周圍的基材開始溶解，蝕孔擴展至5-10微米，形狀較不規則；第三階段，Ti(C, N)晶出物脫落，形成光滑的半球形蝕孔，大小超過10微米。此外，在孔蝕處還觀察到Ni優先溶解的現象，這與孔蝕處的電位和酸性環境有關。總結來說，Ti(C, N)二次相在A286超合金的孔蝕行為中扮演關鍵角色。其周圍基材的溶解以及晶出物的脫落，最終形成穩態孔蝕。這些發現對於進一步改進A286合金的抗腐蝕性能具有重要意義。

A286 superalloy is a material with excellent corrosion resistance and high-temperature strength, widely used in aerospace and energy fields. This study mainly investigates the effect of micron-scale Ti(C, N) on the corrosion behavior of A286 superalloy through electrochemical methods such as potentiodynamic polarization curves and cyclic potentiodynamic polarization curves. Two different heat treatment methods were applied to the A286 superalloy, and 316L stainless steel was selected as the control group. The surface microstructure changes of the materials were observed using optical microscope (OM) and scanning electron microscope (SEM). The chemical composition of the precipitates was analyzed using a transpassive electron microscope (TEM) and energy-dispersive X-ray spectroscopy (EDS). The results show that the constituent particles in the A286 alloy are mainly Ti(C, N), which mostly form around inclusions such as CaO, MgO, and CaS during molten cooling. These Ti(C, N) constituent particles play a crucial role in the pitting corrosion process. Specifically, pitting corrosion in the A286 alloy generally starts from the Ti(C, N) constituent particles and is unrelated to the precipitates formed after solution treatment. Electrochemical tests indicate that, compared to 316L stainless steel, the A286 alloy has an extremely low sulfur content after electro slag remelting, so pitting corrosion is mostly initiated by oxides. Most pits will repassivate, and only a few can grow to a stable stage. Specifically, pitting can be divided into three stages: in the first stage, CaO preferentially dissolves, forming circular pits about 1-2 micrometers in size; in the second stage, the matrix around the Ti(C, N) constituent particles begins to dissolve, expanding the pits to 5-10 micrometers with irregular shapes; in the third stage, the Ti(C, N) constituent particles fall off, forming smooth hemispherical pits larger than 10 micrometers. Moreover, preferential dissolution of Ni at the pitting sites was observed, which is related to the potential and acidic environment at the pitting sites. In summary, the micron-scale Ti(C, N) plays a crucial role in the pitting corrosion behavior of the A286 superalloy. The dissolution of the matrix around the constituent particles and the shedding of the constituent particles eventually form stable pits. These findings are significant for further improving the corrosion resistance of the A286 alloy.