Oxidation‐led decomposition of hexagonal boron nitride coatings on alloy substrates at 900 °C : chromia‐formers

Fleming, Christopher (2019) Oxidation‐led decomposition of hexagonal boron nitride coatings on alloy substrates at 900 °C : chromia‐formers. Materials and Corrosion-Werkstoffe und Korrosion, 70 (5). pp. 853-867. ISSN 0947-5117 (https://doi.org/10.1002/maco.201810532)

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Abstract

In contrast to a mass of powder in air at 900 °C, the oxidation rate of hexagonal boron nitride does not tend to a plateau when present as a coating on austenitic stainless steel type 304 and type 310, and a real-world hot forming tool alloy. As with a mass of powder, a molten boron trioxide diffusion barrier encapsulates each hexagonal boron nitride grain around the basal plane. These subsequently merge to form a dispersion of remnant grains throughout a molten matrix. Boron trioxide is semipermeable, and as such, the substrate oxidizes concurrently. As it does so, outwardly diffusing chromium (III) ions react with boron trioxide to form chromium borate, which depletes the diffusion barrier. This causes the oxidation of hexagonal boron nitride to be sustained at an enhanced rate and the overlayer ultimately undergoes complete decomposition. During this process, the scale comprises chromium borate and chromia only. While manganese chromium spinel and iron chromium spinel form readily at the oxide-atmosphere interface of equivalently heat-treated uncoated substrates, they do not form until after the coating has completely decomposed.

  • Item type:Article
    ID code:66908
    Dates:
    Date
    Event
    1 May 2019
    Published
    25 January 2019
    Published Online
    8 October 2018
    Accepted
    10 November 2016
    Submitted
    Notes:This is the peer reviewed version of the following article: Fleming, C. (2019). Oxidation‐led decomposition of hexagonal boron nitride coatings on alloy substrates at 900 °C: chromia‐formers. Materials and Corrosion-Werkstoffe und Korrosion., which has been published in final form at https://doi.org/10.1002/maco.201810532. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.
    Subjects:Technology > Manufactures
    Department:Faculty of Engineering > Design, Manufacture and Engineering Management
    Depositing user: Pure Administrator
    Date deposited:12 Feb 2019 12:30
    Last modified:08 Apr 2024 23:03
    URI:https://strathprints.strath.ac.uk/id/eprint/66908
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