Small punch test for the mechanical characterization of a cold-sprayed coating

The mechanical characterization of coatings requires miniaturized tests to obtain the stress-strain curve of the coating material unless self-standing specimens are ad hoc manufactured. Hence, the small punch test, which has been recently standardized by ASTM with a disc-shaped specimen of 0.5 mm thickness, could be a valid tool. This test is particularly suitable for metallic coating, allowing for the simple and easy removal of a thin layer. This work investigates the applicability of the small punch test to the characterization of a cold-sprayed coating. Small discs are extracted from a copper coating and experimentally loaded with the bending device prescribed in the standard. Specimens are tested in two conditions: as built and thermally treated to increase ductility. A numerical model of the test is built to fit the load vs displacement curve and obtain the corresponding stress-strain curve. This inverse procedure allows for identifying the elastic modulus, the yield stress, and the ultimate strength, as well as estimating the whole stress-strain curve, similarly to a uniaxial tensile test. As a perspective, this procedure can be applied to select the most suitable cold spray manufacturing parameters and/or the most suitable thermal treatment, hence, optimizing the mechanical performance of the coating.