Nanoindentation and nanoscratch of coatings for concentrated solar power plants for energy generation - nanoscratch
Concentrating solar power systems (CSP) based on the conversion of the solar thermal energy are one of the most promising sources of renewable energy. New CSP systems with improved multilayer absorber coating are now being developed and their durability has to be tested. This application report shows the use of nanoindentation and scratch testing for characterization of nanomechanical properties of the new coatings before and after degradation tests.
This application report is a continuation of the work presented in Part I: Nanoindentation testing of multi-layer coatings for concentrated solar power systems, which was dedicated to nanoindentation testing.
Adhesion by scratch testing
Nanoscratch tests with length of 1.0 mm with progressively increasing normal load (1000 mN/min) from 2 mN to 500 mN were performed by diamond sphero-conical indenter with 10 μm tip radius using the Anton Paar Nano Scratch Tester (NST). A pre-scan and post-scan procedure was included in the scratch in order to eliminate the influence of sample inclination and/or surface profile. In such a way the true penetration and residual depth of the scratch was obtained. After the scratch test the sample was observed with the attached optical microscope and a Panorama image was recorded. The Panorama feature of the Scratch software allows synchronization of the image of the scratch with the recorded signals (friction force, depth, normal force, etc.).
The adhesion (and cohesion) of the coatings was characterized by critical loads (Lc). Critical load Lc is defined as the load that corresponds to the first appearance of a particular type of failure such as cracks or delamination. Usually several critical loads can be determined: the first cracks in the coating (mainly cohesive damage), partial delamination (adhesive failure) and complete delamination (catastrophic adhesive failure).
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