The interfacial indentation test to determine adhesion and residual stresses in NiCr VPS coatings

The interfacial indentation test allows determining the interface toughness of a coating obtained by thermal spraying. During this test, a Vickers indentation is carried out on a cross-section of the sample. A crack is initiated and propagated along the interface. An analytical model allows defining an interface toughness representing the coating adhesion. The objective of this study is to compare this test with other tests (tensile adhesive test, shear test) and to specify its applicability. The residual stresses are also estimated by two different methods. Their influence on adherence is discussed in a third part. Those experiments were conducted on NiCr 80-20 VPS coatings with different thicknesses and roughnesses. In particular, it is shown that the interfacial indentation test is the most universal one and that compressive residual stresses improve coating adhesion.