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Oxidation-Nitridation of chromium at high temperatures and its mitigation by alloying

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  • 130pagine
  • 5 ore di lettura

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This work investigates oxidation and nitridation in the binary Cr-Si system, focusing on the kinetics and thermodynamics of oxidation through a systematic approach. The oxidation and nitridation behavior of individual phases—solid-solution phase (Crss) and silicide phase (A15)—were studied separately, examining short and long-term exposure kinetics, thermodynamic stability, and post-exposure characterization of scale and subscale morphologies. Results indicate that chromium is the primary element in the oxidation process, making these alloys significant chromia formers. Notably, localized SiO₂ formation plays a crucial role in reducing oxidation kinetics, with the oxidation rate of chromium decreasing dramatically with the addition of just 3 at.% Si. The A15 Cr₃Si phase developed a continuous SiO₂ layer during long-term exposure. In a two-phase eutectic alloy, both phases oxidized cooperatively, leading to chromium depletion and the formation of an A15 layer at the alloy-scale interface. The influence of nitrogen as an oxidant was also examined, revealing that a chromium subnitride layer grows via inward nitrogen diffusion, while Si significantly hinders nitridation. The A15 silicide remains stable under high nitrogen pressures and acts as a protective barrier. Further exploration of the ternary Cr-Ge-Si system showed that Ge stabilizes the A15 phase and maintains a fine-lamellar microstructure. This approach notably improved

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Oxidation-Nitridation of chromium at high temperatures and its mitigation by alloying, Ali Soleimani Dorcheh

Lingua
Pubblicato
2017
Rilegatura
(In brossura)
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Metodi di pagamento

Titolo
Oxidation-Nitridation of chromium at high temperatures and its mitigation by alloying
Lingua
Inglese
Editore
Shaker
Pubblicato
2017
Formato
In brossura
Pagine
130
ISBN10
3844050787
ISBN13
9783844050783
Serie
Descrizione
This work investigates oxidation and nitridation in the binary Cr-Si system, focusing on the kinetics and thermodynamics of oxidation through a systematic approach. The oxidation and nitridation behavior of individual phases—solid-solution phase (Crss) and silicide phase (A15)—were studied separately, examining short and long-term exposure kinetics, thermodynamic stability, and post-exposure characterization of scale and subscale morphologies. Results indicate that chromium is the primary element in the oxidation process, making these alloys significant chromia formers. Notably, localized SiO₂ formation plays a crucial role in reducing oxidation kinetics, with the oxidation rate of chromium decreasing dramatically with the addition of just 3 at.% Si. The A15 Cr₃Si phase developed a continuous SiO₂ layer during long-term exposure. In a two-phase eutectic alloy, both phases oxidized cooperatively, leading to chromium depletion and the formation of an A15 layer at the alloy-scale interface. The influence of nitrogen as an oxidant was also examined, revealing that a chromium subnitride layer grows via inward nitrogen diffusion, while Si significantly hinders nitridation. The A15 silicide remains stable under high nitrogen pressures and acts as a protective barrier. Further exploration of the ternary Cr-Ge-Si system showed that Ge stabilizes the A15 phase and maintains a fine-lamellar microstructure. This approach notably improved