Inconel 738超合金在含硫氣氛下之熱循環腐蝕及Na2SO4/V2O5混合鹽熱腐蝕

The Thermal-cycling and Hot Corrosion of Inconel 738 Superalloy in a S2-containing Atmosphere

本研究使用Inconel 738(In-738)鎳基超合金於硫分壓104 Pa之氣氛，850℃-100℃之高低溫進行熱循環腐蝕，並另以表面噴塗質量比3：1之Na2SO4及V2O5，於750~850℃相同硫分壓進行混合鹽之恆溫熱腐蝕試驗，藉此探討合金之熱腐蝕行為。研究結果顯示合金於熱循環高溫硫化動力學遵守拋物線型定律，且其腐蝕速率隨循環次數的增加而降低。合金於混合鹽之恆溫熱腐蝕動力學亦呈拋物線型定律，隨溫度之上升，其腐蝕反應速率呈緩慢增加之趨勢。合金經第一次熱循環腐蝕後，表面生成之腐蝕物為塊狀的Ni3S2 及微量的Co3S4及Cr2S3/Cr3S4，內層腐蝕物主要為Ni3S2、微量的Al2S3與CoCr2S，經過多次熱循環腐蝕後，表面則生成球狀的Ni3S2及少許的Co3S4及Cr2S3/Cr3S4，其內層亦為Ni3S2、微量的Al2S3與CoCr2S4。合金經混合鹽恆溫熱腐蝕後，腐蝕生成物主要為Ni3S2，Cr2S3及氧化物（含NiO、Cr2O3及Al2O3）。由於氧化物的形成，使合金熱腐蝕之速率低於單純的高溫硫化。

The purpose of the research is to study the thermal-cycling corrosion behavior of In-738 superalloy at Ps2=104 Pa (The cycling period is at 850℃ for 1 hr and at 100℃ for 1 hr), and the hot corrosion behavior of the alloy over the temperature range of 750~850℃ at Ps2=104 Pa with mixed coating of Na2SO4/V2O5 (at the weight ratio of 3 1). The thermal-cycling corrosion kinetics followed the parabolic rate law, and the corrosion rates decreased with increasing cycling times. The hot corrosion kinetics also followed the parabolic rate law, and the corrosion rates slowly increased with increasing temperature. The scale formed on topograph of the first thermalcycling specimens is main feather-shaped Ni3S2 and minor amounts of Co3S4 and Cr2S3 /Cr3S4, while the inner layer was a heterophasic mixture of Ni3S2, Al2S3, and CoCr2S4. however, the bignoduleshaped Ni3S2 is observed after several cycling-times. In addition, the scales formed on the hot corrosion of In-738 consisted of mostly Ni3S2, Cr2S3 and some oxides of NiO, Cr2O3, and Al2O3.