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.

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.

Citation

Jackson, G., Sun, W., & McCartney, D. (2019). Influence of microstructure on the ductile to brittle transition and fracture behaviour of HVOF NiCoCrAlY coatings determined via small punch tensile testing. Journal of Materials Science and Engineering A, 754, 479-490. https://doi.org/10.1016/j.msea.2019.03.108

• 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.
• Contract Date: Apr 1, 2019