Diffusion, defects and understanding the growth of a multicomponent interdiffusion zone between Pt-modified B2 NiAl bond coat and single crystal superalloy

Esakkiraja, N and Gupta, A and Jayaram, V and Hickel, T and Divinski, SV and Paul, A (2020) Diffusion, defects and understanding the growth of a multicomponent interdiffusion zone between Pt-modified B2 NiAl bond coat and single crystal superalloy. In: Acta Materialia, 195 (15). pp. 35-49.

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Abstract

Composition-dependent diffusion coefficients are determined in B2-Ni(CoPt)Al system following the pseudo-binary and pseudo-ternary diffusion couple methods, which would not be possible otherwise in a quaternary inhomogeneous material fulfilling the conditions to solve the equations developed based on the Onsager formalism. The end-member compositions to produce ideal/near-ideal diffusion profiles are chosen based on thermodynamic details. The pseudo-binary interdiffusion coefficients of Ni and Al decrease in the presence of Co but increase in the presence of Pt. The pseudo-ternary interdiffusion coefficients indicate that the main interdiffusion coefficients increase significantly in the presence of Pt. Marginal changes of the cross interdiffusion coefficients substantiate a minor change of the diffusional interactions between the components. The thermodynamic driving forces show opposite trends with respect to composition as compared to the changes of the interdiffusion coefficients advocating a dominating role of the Pt(Co)-induced modifications of point defect concentrations. DFT-based calculations revealed that Pt alloying increases the Ni vacancy concentration and decreases the activation energy for the triple defect diffusion mechanism. These findings explain the increase in the thickness of the interdiffusion zone between the B2-Ni(Pt)Al bond coat and the single crystal superalloy René N5 because of Pt addition. Furthermore, the EPMA and TEM analyses reveal the growth of refractory elements-enriched precipitates. © 2020 Acta Materialia Inc.

Item Type:	Journal Article
Publication:	Acta Materialia
Publisher:	Acta Materialia Inc
Additional Information:	Copy right for this article belongs to Acta Materialia Inc
Keywords:	Activation energy; Aluminum alloys; Binary alloys; Defects; Diffusion; Single crystals; Superalloys, Defect concentrations; Diffusional interactions; Inhomogeneous materials; Inter-diffusion coefficients; Refractory elements; Single crystal superalloys; Thermodynamic driving forces; Vacancy concentration, Platinum alloys
Department/Centre:	Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited:	30 Sep 2020 07:02
Last Modified:	30 Sep 2020 07:02
URI:	http://eprints.iisc.ac.in/id/eprint/65703

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