Next-generation supercritical CO₂ (sCO₂) power cycles will require different classes of alloy throughout the operational temperatures to optimize tradeoff of creep strength, oxidation performance and cost. This will necessitate joining methods such as welding, which might pose compatibility concerns at the joined interfaces. In this study, similar and dissimilar metal welds were generated from a variety of candidate alloys for sCO₂ systems including ferritic/martensitic steels, austenitic steels, and Ni-based superalloys. Samples were extracted from different regions of the welds and exposed to sCO₂ at 550 °C and 20 MPa for 2500 h and then characterized to understand their behavior in this environment. Unsurprisingly, the local oxidation behavior was largely dictated by the Cr content in the underlying metal. High-Cr austenitic steels and Ni alloys formed slow-growing Cr-rich oxide scales with minimal carburization of the underlying metal, while low-Cr ferritic/martensitic steels formed fast-growing Fe-rich oxide scales with significant carburization. Most welds did not show any unusual oxidation behavior at the interfaces, considering the local Cr content. The one exception was the 347H similar metal weld, where a larger grain size and complex grain structure in the fusion zone led to a significantly higher rate of Fe-rich oxide nodule formation compared to the base metal. This suggests that microstructural changes at joined interfaces can play an important role on the oxidation-limited lifetimes in future sCO₂ systems. The composition changes across the interfaces enabled study of the effect of Fe on the growth rate of Cr-rich oxides and of the origins of the subsurface recrystallization zone that forms beneath them.

下一代超临界 CO ₂ (sCO ₂ ) 动力循环将需要在整个操作温度范围内使用不同类别的合金，以优化蠕变强度、氧化性能和成本的权衡。这将需要连接方法，例如焊接，这可能会在连接的界面上引起兼容性问题。在这项研究中，类似和不同的金属焊缝是从各种 sCO ₂系统的候选合金中产生的，包括铁素体/马氏体钢、奥氏体钢和镍基高温合金。从焊缝的不同区域提取样品并暴露于 sCO ₂在 550 °C 和 20 MPa 下持续 2500 小时，然后表征以了解它们在该环境中的行为。不出所料，局部氧化行为很大程度上取决于底层金属中的 Cr 含量。高铬奥氏体钢和镍合金形成缓慢生长的富铬氧化皮，底层金属的渗碳最少，而低铬铁素体/马氏体钢形成快速生长的富铁氧化皮，渗碳显着。考虑到局部 Cr 含量，大多数焊缝在界面处没有表现出任何异常的氧化行为。一个例外是 347H 类似金属焊缝，与母材相比，熔合区中较大的晶粒尺寸和复杂的晶粒结构导致富铁氧化物瘤形成率明显更高。_2个系统。界面上的成分变化有助于研究 Fe 对富铬氧化物生长速率的影响以及在它们下方形成的表面下再结晶区的起源。