Effect of Specimen Thickness on Microstructural Changes During Oxidation of the NiCrW Alloy 230 at 950–1050°C

Journal Article · Fri Sep 25 00:00:00 EDT 2015 · Journal of The Minerals, Metals & Materials Society

DOI:https://doi.org/10.1007/s11837-015-1645-8· OSTI ID:1265880

Jalowicka, A. ^[1]; Duan, R. ^[1]; Huczkowski, P. ^[1]; Chyrkin, A. ^[1]; Grüner, D. ^[1]; Pint, B. A. ^[2]; Unocic, K. A. ^[2]; Quadakkers, W. J. ^[1]

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1. Julich Research Centre (Germany)
2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

An accurate procedure for predicting oxidation-induced damage and lifetime limits is crucial for the reliable operation of high-temperature metallic components in practical applications. In order to develop a predictive oxidation lifetime model for Ni–Cr alloys, specimens of wrought NiCrW alloy 230 with different thicknesses were cyclically oxidized in air at 950–1050°C for up to 3000 h. After prolonged exposure, two types of carbides as well as a Cr-rich nitride (π-phase) precipitated in the γ-Ni matrix. In the case of oxidation-induced loss of Cr from the alloy resulted in the formation of subscale zones, which were free of the Cr-rich carbide and nitride but also of the Ni-W rich M₆C. The width of the M₆C-free zone was smaller than that free of the Cr-rich precipitates. Thermodynamic and diffusion calculations of the observed time- and temperature-dependent Cr depletion processes identified that back diffusion of C occurred which resulted in an increased volume fraction of M₂₃C₆ in the specimen core. Moreover, with increasing time and temperature, the amount of π-phase in the specimen core increased. The subscale depletion of the initially present Cr-nitrides and the formation of Cr-nitrides in the specimen center is believed to be related to a mechanism which is qualitatively similar to that described for the Cr carbide enrichment. However, with increasing time and decreasing specimen thickness, N uptake from the atmosphere becomes apparent. As a result, the precipitates present in the specimen center eventually consisted almost exclusively of nitrides.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE)
• Grant/Contract Number: AC05-00OR22725; 03EK3032
• OSTI ID: 1265880
• Journal Information: Journal of The Minerals, Metals & Materials Society, Vol. 67, Issue 11; ISSN 1047-4838
• Publisher: Springer
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
NiCr alloys
oxidation
lifetime model
thermodynamics
kinetics