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Infrared Thermography as a Non-destructive Testing Solution for Thermal Spray Metal Coatings

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Details

Original languageEnglish
Pages (from-to)1982–1993
Number of pages12
JournalJournal of Thermal Spray Technology
Volume26
Issue number8
Early online date15 Sep 2017
DOIs
Publication statusPublished - Dec 2017
Publication typeA1 Journal article-refereed

Abstract

In this work, an infrared (IR) thermographic procedure was evaluated as a non-destructive testing tool to detect damage in thermal spray metallic coatings. As model systems, polished HVOF- and HVAF-sprayed Fe-based layers deposited onto steel plates were employed. Damage by external-object impingement was simulated through a cyclic impact-test apparatus, which induced circumferential and radial cracks across all model systems, and interface cracks of different sizes in distinct samples. Damaged and undamaged plates were bulk-heated to above 100 °C using an IR lamp; their free-convection cooling was then recorded by an IR thermocamera. The intentionally induced defects were hardly detectable in IR thermograms, due to IR reflection and artificial “hot” spots induced by residuals of transfer material from the impacting counterbody. As a micrometer-thin layer of black paint was applied, surface emissivity got homogenized and any artifacts were effectively suppressed, so that failed coating areas clearly showed up as “cold spots.” This effect was more apparent when large interface cracks occurred. Finite-element modeling proved the physical significance of the IR-thermography approach, showing that failed coating areas are cooled by surrounding air faster than they are heated by conduction from the hot substrate, which is due to the insulating effect of cracks.

Keywords

  • finite element modeling, high-velocity air fuel (HVAF), high-velocity oxy fuel (HVOF), impact testing, non-destructive inspection

Publication forum classification

Field of science, Statistics Finland