Paint adhesion testing

Abstract: Cell adhesion and spreading of chick embryo vascular and corneal explants grown on rough and smooth poly (methyl methacrylate) (PMMA) were analyzed to test the cell response specificity to substratum surface properties. Different degrees of roughness were obtained by sand-blasting PMMA with alumina grains. Hydrophilic and hydrophobic components of the surface free energy (SFE) were calculated according to Good-van Oss's model. Contact angles were determined using a computerized angle meter. The apolar component of the SFE gamma s(LW), increased with a slight roughness whereas the basic component, gamma s-, decreased. The acido-basic properties disappeared as roughness increased. Incubation of PMMA in culture medium, performed to test the influence if the biological environment, allowed surface adsorption of medium proteins which annihilated roughness effect and restored hydrophilic properties. An organotypic culture assay was carried out in an attempt to relate the biocompatibility to substratum surface state. Cell migration was calculated from the area of cell layer. Cellular adhesion was determined by measuring the kinetic of release of enzymatically dissociated cells. A slight roughness raised the migration are to an upper extent no matter which cell type. Enhancement of the cell adhesion potential was related to the degree of roughness and the hydrophobicity.

Abstract: The scratch test has been used to assess coating adhesion for some time. In this test, a diamond indenter is drawn across the coated surface under an increasing load (either stepwise or continuous) until at some load, termed the critical load L c , a well-defined failure event occurs; if this failure event represents the loss of coating-substrate adhesion then the critical load can be used as a qualitative measure of coating-substrate adhesion. However, it is well known that a range of possible failure modes can occur and only some of these are dependent on adhesion; other failure modes which depend on plastic deformation and fracture within the coating, rather than any adhesive failure at the coating-substrate interface, may be just as useful in the assessment of coating quality for tribological applications. In this study, titanium nitride coatings have been deposited onto a range of different substrates from soft nickel to a hard cemented carbide and the failure modes which occur during scratch testing have been identified. Failures fall into two general groups, depending on whether the substrate behaves in a brittle or ductile manner during the scratch test. Similar failure modes are observed for titanium nitride coatings produced by several deposition technologies, although there is some variation in the appearance of specific failures which is process dependent. Many of the same failure modes are also observed for other coating materials, such as ZrN or hard carbon, but several different types of failure are also observed. The generation of acoustic emission during the test is related to the occurrence of these different failure modes. The origin of the failure modes and the use of the scratch test to assess coating-substrate adhesion are discussed in the light of these observations.