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  • 1.  Non-destructive Characterization and Adhesion Strength of Thermally Sprayed Coatings

    Posted 05-31-2022 14:14

    Dear Thermal Spray Community, 

    Would anyone have advice or studies to share that may relate non-destructive characterization of thermally sprayed coatings to the coating bonding strength ? From my current experience, it seems that non-destructive techniques like ultrasounds (UT) may give a degree of "pass/fail" information, but it doesn't seem possible to relate/assess if the coating may perform as desired, without having conducting extensive mechanical testing.

    Thanks in advance for any suggestions you may be able to provide !



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    Andre Liberati
    Research Assistant
    Concordia University
    Montréal QC
    (514) 813-8021
    andre.liberati@concordia.ca
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  • 2.  RE: Non-destructive Characterization and Adhesion Strength of Thermally Sprayed Coatings

    Posted 06-01-2022 15:44
    Hi Andre,
    All testing is based on sampling, and on knowledge of the relationship of the sample and test to the performance of a real-world part.  If a real-world part is tested in the identical environment to the intended service, your knowledge of the performance is 100% certain.  All other tests, samples, and inspections are approximations or correlations based on inferences or past knowledge.  Even a tensile test, a direct and destructive test, is of value only when a designer knows that it will be sufficient for material properties in that test direction and condition to serve adequately. 
    Using an inspection process gives one data but there has to be previously obtained knowledge that the test when applied, will give data that is meaningfully correlated with real-world performance.  This is how codes and standards are developed.
    So for example, UT at a-frequency from b-sized transducer coupled with c-coupling method scanned in d-direction using e-examination method will detect f-indication which has been shown in testing to be a significant flaw in g-service.  Unless you have the knowledge tying the material characteristic and detectable indication together to the service, all of the fancy inspection specification values of a- through f- will not give much value.  So you can only specify a coating test with the background of past tests that have been shown to match test results with performance.  And a Pass/Fail to a NDT criterion only sorts your data, it is not meaningful unless it shows that there is value in doing the test. 
    I can see it! = detectable    It's this size/value! = evaluated within the limits of the method  It's rejectable! = a meaningful evaluation has been done compared to criteria set from knowledge and experience.

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    Paul Tibbals
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  • 3.  RE: Non-destructive Characterization and Adhesion Strength of Thermally Sprayed Coatings

    Posted 06-03-2022 11:28

    Hi Paul, 

    Thank you for very much for your insights here, I appreciate the in-depth perspective you provide to the question. I guess it goes back to really defining the question of "What is desired of this system ?" and then only "How do I assess it is performing as expected ? What are the requirements to confirm performance ?". It's interesting as on the academic research side we tend to spend a lot of time pondering a- through f-, and while this is natural to some extent, defining g- is the most important for achieving any form of application. I will definitely keep this in mind in my future considerations. 



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    Andre Liberati
    Research Assistant
    Concordia University
    Montréal QC
    (514) 813-8021
    andre.liberati@concordia.ca
    ------------------------------