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On the crystallography and composition of topologically close-packed phases in ATI 718Plus®

Published version
Peer-reviewed

Type

Article

Change log

Authors

Johnstone, DN 
Eggeman, AS 
Hünert, D 
Hardy, MC 

Abstract

ATI 718Plus® is a nickel-based superalloy developed to replace Inconel 718 in aero engines for static and rotating applications. Here, the long-term stability of the alloy was studied and it was found that topologically close-packed (TCP) phases can form at the γ-η interface or, less frequently, at grain boundaries. Conventional and scanning transmission electron microscopy techniques were applied to elucidate the crystal structure and composition of these TCP precipitates. The precipitates were found to be tetragonal sigma phase and hexagonal C14 Laves phase, both being enriched in Cr, Co, Fe and Mo though sigma has a higher Cr and lower Nb content. The precipitates were observed to be heavily faulted along multiple planes. In addition, the disorientations between the TCP phases and neighbouring η/γ were determined using scanning precession electron diffraction and evaluated in axis-angle space. This work therefore provides a series of compositional and crystallographic insights that may be used to guide future alloy design.

Description

Keywords

Ni-based superalloys, intermetallic phases, phase composition, orientation relationship, electron diffraction

Journal Title

Acta Materialia

Conference Name

Journal ISSN

1359-6454
1873-2453

Volume Title

130

Publisher

Elsevier
Sponsorship
Engineering and Physical Sciences Research Council (EP/H022309/1)
European Research Council (291522)
Engineering and Physical Sciences Research Council (EP/H500375/1)
Engineering and Physical Sciences Research Council (EP/L015978/1)
European Commission (312483)
Engineering and Physical Sciences Research Council (EP/M005607/1)
The authors acknowledge Rolls-Royce plc, the EPSRC and the BMWi under grants EP/H022309/1, EP/H500375/1 and 20T0813. P.A.M acknowledges financial support from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement 291522-3DIMAGE, the Seventh Framework Programme of the European Commission: ESTEEM2, contract number 312483. DNJ acknowledges financial support from the University of Cambridge through the Cambridge Home & EU Scholarship scheme and the EPSRC Cambridge NanoDTC EP/L015978/1.