Concentration-gradient-driven anisotropic spinodal decomposition kinetics: 
nitriding of metallic alloys

Sasidhar, K. N.; Gururajan, M.P.; Meka, Sai Ramudu

doi:10.1080/09500839.2021.1948130

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Concentration-gradient-driven anisotropic spinodal decomposition kinetics: nitriding of metallic alloys

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Sasidhar, K. N.
Microstructure Physics and Alloy Design, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society;
Department of Metallurgical and Materials Engineering, Indian Institute of Technology Roorkee (IIT Roorkee), Roorkee 247667, India;

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Citation

Sasidhar, K. N., Gururajan, M., & Meka, S. R. (2021). Concentration-gradient-driven anisotropic spinodal decomposition kinetics: nitriding of metallic alloys. Philosophical Magazine Letters, 101(11), 432-443. doi:10.1080/09500839.2021.1948130.

Cite as: https://hdl.handle.net/21.11116/0000-0009-7131-0

Abstract

The effect of crystallographically oriented, unidirectional concentration gradients on spinodal decomposition in cubic crystalline solids with elastic and interfacial energy anisotropy is discussed. Phase-field simulations reveal that the kinetics of spinodal decomposition occurring in such systems is dependent on the degree of misorientation between the direction of composition gradient and the preferred crystallographic orientation for growth of spinodal fluctuations; the larger is the misorientation, the slower the kinetics. This phenomenon has been used to explain the well-known grain-orientation-dependent N-uptake kinetics observed during nitriding of metallic alloys. Several plausible causes have been proposed in the literature for the grain-orientation-dependent N-uptake kinetics during nitriding. However, this study reveals that this phenomenon is observed exclusively and without exception in alloy systems having a spinodal instability. The N-uptake kinetics in such systems is known to be dependent on the kinetics of spinodal decomposition. Consequently, anisotropic spinodal decomposition kinetics occurring owing to the presence of a surface-directed N-composition gradient in poly-crystalline metals has been shown to be a more fundamental cause for the phenomenon. © 2021 Informa UK Limited, trading as Taylor Francis Group.