Role of threshold stress in creep of IN740H, a γ�-lean Ni-based superalloy

Kumar, C and Pavan, AHV and Makineni, SK and Kumar, P (2024) Role of threshold stress in creep of IN740H, a γ�-lean Ni-based superalloy. In: Materials Science and Engineering: A, 903 .

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Abstract

IN740H, a Ni-based superalloy comprising a low-volume fraction of γ�, is a candidate material to be used over long periods at high temperatures and stresses, as conditions prevalent in advanced ultra-supercritical (AUSC) power plants. In this study, IN740H has been tested at temperatures above 700 °C to gain mechanistic insights into its high-temperature creep behavior. The material showed classic signatures of the presence of threshold stress, marked by observation of a high apparent creep stress exponent, n, (e.g., 10 at 750 °C) and a high apparent activation energy for creep, Qc (e.g., �545 kJ/mol), along with a rapid increase in n at lower stresses. Accounting for the threshold stress led to a decrease in the values of n and Qc to 4 and 280 kJ/mol, respectively. Furthermore, the transmission electron microscopy and atomic scale compositional analysis reveal the pinning of dislocations at γ-γ� interface and segregation of Co, Cr and Mo atoms in the regions of γ-γ� interface rich in dislocations. The above combination of n and Qc and the observation of dislocation pinning at the γ-γ� interface indicate the dislocation climb over γ� as the dominant creep mechanism in this γ�-lean Ni-based superalloy, with the detachment of dislocations from the γ-γ� interface, augmented by the segregation of Co, Cr and Mo, as the mechanism responsible for the realization of the threshold stress. This work, thus, provides a new impetus to research on the long-term structural integrity of γ�-lean Ni-based superalloys exposed to extreme service conditions. © 2024 Elsevier B.V.

Item Type:	Journal Article
Publication:	Materials Science and Engineering: A
Publisher:	Elsevier Ltd
Additional Information:	The copyright for this article belongs to Elsevier Ltd
Keywords:	Activation energy; High resolution transmission electron microscopy; Nickel alloys; Superalloys, Candidate materials; Dislocation climb; Dislocation climb creep; Dislocation interaction; Highest temperature; Ni-based superalloys; Precipitate-dislocation interaction; Solute segregation; Threshold stress; ��-lean ni-based superalloy, Creep
Department/Centre:	Division of Interdisciplinary Sciences > Interdisciplinary Centre for Energy Research Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited:	29 Jul 2024 05:07
Last Modified:	29 Jul 2024 05:07
URI:	http://eprints.iisc.ac.in/id/eprint/85179

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