Corrosion Behavior of Selected Structural Materials in a Simulated Steam-Cycle High-Temperature Gas-Cooled Reactor Helium Environment

Mazandarany, F. N.; Lai, G.Y.

doi:10.13182/nt79-a19223

Cited by 11 publications

(1 citation statement)

References 5 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…[28,39,41,[59][60][61][62][63] Typically, the mole fraction of carbon (X C ) in solid solution is related to the carbon activity (a C ) according to the linear Henry's law a C = c C 0 X c , where c C 0 is the Raoultian activity coefficient for carbon that is dependent on temperature (and is independent of a C ). [59] Furthermore, it has been shown that, for low Cr-containing Ni-Cr alloys, log(c C 0 ) depends linearly on the reciprocal absolute temperature 1/T for Cr content between 5 wt pct and 13 wt pct.…”

Section: =6mentioning

confidence: 99%

Chromia-Assisted Decarburization of W-Rich Ni-Based Alloys in Impure Helium at 1273 K (1000 °C)

Adharapurapu

Kumar

Zhu

et al. 2010

Metall Mater Trans A

View full text Add to dashboard Cite

The microstructure and surface stability of two experimental W-rich Ni-based alloys have been studied at 1273 K (1000°C) in an impure-He environment containing only CO and CO 2 as impurities. The alloy Ni-2.3Al-12Cr-12W contained 0.08 wt pct carbon in solution, whereas the second alloy Ni-2.3Al-3Mo-12Cr-12Co-12W contained M 6 C carbides at the same carbon level. Both alloys, which were preoxidized with~2.3 lm Cr 2 O 3 layer, were decarburized completely within 50 hours of exposure to the helium gas mixture at 1273 K (1000°C) via the following chromia-assisted decarburization reaction: Cr 2 O 3 (s) + 3C alloy (s) fi 2Cr (s) + 3CO (g). Microstructural observations, bulk carbon analysis, and microprobe measurements confirmed that the carbon in solid solution reacted with the surface chromium oxide resulting in the simultaneous loss of chromia and carbon. The Cr produced by the decomposition of the Cr 2 O 3 diffused back into the alloy, whereas CO gas was released and detected by a gas chromatograph. Once the alloy carbon content was reduced to negligible levels, subsequent exposure led to the uninterrupted growth of Cr 2 O 3 layer in both alloys. In the preoxidized alloys, chromia-assisted decarburization rates were slower for an alloy containing carbides compared with the alloy with carbon in solid solution only. The formation of Cr 2 O 3 is shown to be the rate-limiting step in the chromia-assisted decarburization reaction. Exposure of as-fabricated alloys to the impure-He environment led to the formation of a thin layer of Al 2 O 3 (<1 lm) between the substrate and surface Cr 2 O 3 oxide that inhibited this decarburization process by acting as a diffusion barrier.

show abstract