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influence of microstructure on the ductile to brittle transition and fracture behaviour of HVOF NiCoCrAlY coatings determined via small punch tensile testing

Jackson, G.A.; Sun, W.; McCartney, D.G.

 influence of microstructure on the ductile to brittle transition and fracture behaviour of HVOF NiCoCrAlY coatings determined via small punch tensile testing Thumbnail


Authors

G.A. Jackson

W. Sun

D.G. McCartney



Abstract

The development of new thermal barrier coatings (TBC’s) capable of increasing the efficiency of gas-powered turbines requires an understanding of how the tensile behavior and ductile to brittle transition temperature (DBTT) of MCrAlY bond coats are influenced by the coating microstructure. High velocity oxy-fuel (HVOF) thermal spraying was used to manufacture free-standing coatings from two NiCoCrAlY alloys that have potential as new bond coat alloys, referred to as coatings BC1 and BC2. The coatings were vacuum heat treated at 1100 °C for 2 hours and characterised using X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron back-scatter diffraction (EBSD). Both coatings comprised a BCC β-NiAl matrix with FCC γ-Ni and TCP σ-Cr2Co as secondary phases. Coating BC2 also contained FCC γ’-Ni3Al. Small punch tensile (SPT) tests were conducted on the coatings between RT and 750 °C. The DBTT’s of coatings BC1 and BC2 were found to be 600-700 °C and 650-750 °C respectively. Lower phase fractions of γ-Ni were shown to increase the DBTT. The main mode of crack propagation in both coatings was intergranular fracture along the grain boundaries of differing phases. The influence of coating microstructure on the fracture behavior of both coatings was discussed using schematic models.

Journal Article Type Article
Acceptance Date Mar 25, 2019
Online Publication Date Mar 26, 2019
Publication Date Apr 29, 2019
Deposit Date Apr 1, 2019
Publicly Available Date Mar 27, 2020
Journal Materials Science and Engineering: A
Print ISSN 2161-6213
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 754
Pages 479-490
DOI https://doi.org/10.1016/j.msea.2019.03.108
Keywords Small punch tensile testing; NiCoCrAlY; McrAlY; HVOF; DBTT; Fracture; Mechanical properties
Public URL https://nottingham-repository.worktribe.com/output/1722337
Publisher URL https://www.sciencedirect.com/science/article/pii/S0921509319304216
Additional Information This article is maintained by: Elsevier; Article Title: The influence of microstructure on the ductile to brittle transition and fracture behaviour of HVOF NiCoCrAlY coatings determined via small punch tensile testing; Journal Title: Materials Science and Engineering: A; CrossRef DOI link to publisher maintained version: https://doi.org/10.1016/j.msea.2019.03.108; Content Type: article; Copyright: © 2019 Published by Elsevier B.V.

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