Effect of systematic variation in Co:Ni ratio on elemental partitioning, lattice misfit and oxidation behaviour of γ'-strengthened (Ni,Co)75Al5Ti5Cr15 (at.%) alloys
type: CreativeWork
description: Ni-based superalloys currently in-service as aero-engine turbine discs are operating at the limit of their high-temperature capability. Next-generation turbine disc superalloys must be capable of sustaining the higher operating temperatures (approaching 800°C) and stresses required for greater thermal efficiency, whilst maintaining mechanical integrity and excellent oxidation resistance. Studies on the emerging γ'-strengthened Co-based superalloys based on the Co-Al-W and Co-Al-Mo-Nb/Ta systems have been successful in mitigating the respective drawbacks of high mass density and low γ' solvus temperature by incorporation of Ni, Ti or Cr. However, systematic investigation of the fundamental quinary system, Ni-Co-Al-Ti-Cr, is essential to provide a baseline against which to compare the influence of higher-order alloying with elements, such as W, that potentially confer superior high-temperature properties. To this end, seven γ'-strengthened model superalloys of composition (Ni,Co)75Al5Ti5Cr15 (at.%) were fabricated, aged at 800°C for 1000 hours, and the effect of increasing Co:Ni ratio on their resultant microstructural characteristics and critical properties was determined. For alloys of Co content 0, 9, 19, 28, 38, 47 and 56 at.%, γ' solvus temperature decreased with increasing Co:Ni ratio, whilst alloy mass density remained fairly constant across the alloy series at ~8.1 g.cm-3. Atom probe tomography (APT) was used to determine the elemental partitioning behaviour and γ' volume fraction for each of the seven alloys, denoted 0Co, 9Co, 19Co, 28Co, 38Co, 47Co and 56Co. From APT, a non-monotonic trend in Ti, Al and Cr partitioning was observed as Co:Ni ratio increased, with a transition at ~19 at.% Co. From neutron diffraction analysis, the γ-γ' lattice misfits of alloys 0-47Co were found to be positive at all test temperatures (ambient, 400, 600, 700 and 800°C) and the magnitude of lattice misfit increased as Co content increased from 0-38 at.%. Lattice misfit values d…
abstract: Ni-based superalloys currently in-service as aero-engine turbine discs are operating at the limit of their high-temperature capability. Next-generation turbine disc superalloys must be capable of sustaining the higher operating temperatures (approaching 800°C) and stresses required for greater thermal efficiency, whilst maintaining mechanical integrity and excellent oxidation resistance. Studies on the emerging γ'-strengthened Co-based superalloys based on the Co-Al-W and Co-Al-Mo-Nb/Ta systems have been successful in mitigating the respective drawbacks of high mass density and low γ' solvus temperature by incorporation of Ni, Ti or Cr. However, systematic investigation of the fundamental quinary system, Ni-Co-Al-Ti-Cr, is essential to provide a baseline against which to compare the influence of higher-order alloying with elements, such as W, that potentially confer superior high-temperature properties. To this end, seven γ'-strengthened model superalloys of composition (Ni,Co)75Al5Ti5Cr15 (at.%) were fabricated, aged at 800°C for 1000 hours, and the effect of increasing Co:Ni ratio on their resultant microstructural characteristics and critical properties was determined. For alloys of Co content 0, 9, 19, 28, 38, 47 and 56 at.%, γ' solvus temperature decreased with increasing Co:Ni ratio, whilst alloy mass density remained fairly constant across the alloy series at ~8.1 g.cm-3. Atom probe tomography (APT) was used to determine the elemental partitioning behaviour and γ' volume fraction for each of the seven alloys, denoted 0Co, 9Co, 19Co, 28Co, 38Co, 47Co and 56Co. From APT, a non-monotonic trend in Ti, Al and Cr partitioning was observed as Co:Ni ratio increased, with a transition at ~19 at.% Co. From neutron diffraction analysis, the γ-γ' lattice misfits of alloys 0-47Co were found to be positive at all test temperatures (ambient, 400, 600, 700 and 800°C) and the magnitude of lattice misfit increased as Co content increased from 0-38 at.%. Lattice misfit values d…
author: Llewelyn, Sioned Catherine Huxley
language: eng
keywords: Nickel, Cobalt, Superalloys, Systematic, Elemental partitioning, Atom probe tomography, Lattice misfit, Neutron diffraction, Oxidation
license: https://www.repository.cam.ac.uk/bitstreams/14c60670-9345-4a35-b295-c718f76ab93a/download
license: https://www.rioxx.net/licenses/all-rights-reserved/
date published: 2019-09-01
date modified: 2026-07-22T22:23:57Z
provider: Cambridge University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Cambridge

PropertyValue
property ID: DOI
value: 10.17863/CAM.53219