鎳基超合金於高溫混合氣氛H2/H2S/H2O下之腐蝕行為研究

The Corrosion of Some Inconel Superalloys in a H2/H2S/H2O Gas Mixture

本論文探討四式英高鎳超合金，含Inconel 600, 690, 718及738合金（In-600、690、718、738）在溫度500～850℃，於混合氣氛H2/H2S/H2O下之腐蝕行為。結果顯示，所有英高鎳超合金的腐蝕動力學皆遵守拋物線型定律，且其腐蝕反應速率皆隨溫度之升高而加快，而腐蝕速率高低亦因合金的種類而異，其中In-600及In-718於各溫度之腐蝕率皆較In-690與In-738為快；而In-738與In-690的腐蝕速率極為接近。英高鎳超合金在高溫腐蝕下主要生成內、外兩層腐蝕層，且產生多而複雜的腐蝕物。其中In-600、In-690及In-718外層主要生成硫化鎳（Ni3S2）、硫化鐵鎳（(Fe,Ni)9S8）及微量的硫化鐵（Fe1-xS），而內層主要生成硫化鎳鉻（NiCr2S4）、硫化鉻（Cr2S3/Cr3S4）及少量的硫化鐵鎳（(Fe,Ni)9S8）；於In-718內層亦發現少量的硫化鐵鉬（FeMo2S4）；In-738外層腐蝕生成物主要為硫化鎳（Ni3S2）及少量的硫化鈷（CO9S8）；而內層的腐蝕生成物，主要為硫化鉻（Cr2S3/Cr3S4）、硫化鋁（Al2S3）及微量的硫化鈷鎳（CoNi2S4）；另在各式合金之內層腐蝕物中皆有發現少量的Cr2O3。四式英高鎳超合金於白金指標實驗中，發現其位置皆位於內層與外層腐蝕層之間，顯示外層硫化物生成主要是由陽（鎳、鐵、鉻及鈷等）離子向外擴散所致，而內層硫化層的形成是由陰（硫）離子向內擴散所致。

The purpose of this research is to study the corrosion behavior of four Inconel superalloys (containing In-600, In-690, In-718, and In-738) over the temperature range 500~850℃ in a H2/H2S/H2O gas mixture. The corrosion kinetics of all superalloys followed the parabolic rate law at all temperatures, and the corrosion rate constants increased with increasing temperature. The corrosion rates of In-600 and In-718 were faster than those of In-690 and In-738, while the corrosion rate constants of In-690 and In-738 were nearly identical at all temperatures studied. The scales formed on the alloys were complex and heterophasic, consisting of the outer and inner layers. The outer scales of In-600 consisted of mostly nickel sufide (Ni3S2), (Fe,Ni)9S8, and minor Fe1-xS, while the inner layer was a heterophasic mixture of mostly NiCr2S4, Cr2S3/Cr3S4, and minor (Fe,Ni)9S8. The outer scales of In-690 consisted of nickel sufide (Ni1-xS) and (Fe,Ni)9S8, while the inner layer was a heterophasic mixture of mostly Cr2S3/Cr3S4, NiCr2S4, FeCr2S4, and minor (Fe,Ni)9S8. The outer scales of In-718 consisted of (Fe, Ni)9S8, Ni3S2, and minor Fe1-xS, while the inner layer was a heterophasic mixture of Cr2S3/Cr3S4, some FeMo2S4, and minor Fe1-xS. The outer scales of In-738 consisted of nickel sufide (Ni3S2) and some Co9S8, while the inner layer was a heterophasic mixture of Cr2S3/Cr3S4, some Al2S3, and minor CoNi2S4. In addition, small amounts of Cr2O3 were always detected in the inner-scale layer of all alloys. Platinum markers were always located at the interface between the inner and outer scales, suggesting that the outer scale grew by outward transport of cations (Ni, Fe, Cr, and Co) and the inner scale grew by the inward diffusion of sulfur.