Methods for studying the mechanical and tribological properties of hard and soft coatings with a Nano-Indenter

This study illustrates the capabilities of a nanoindentation /nanoscratch tester to assess mechanical and tribological properties of coating films. Properties such as hardness, elastic modulus, mar and scratch resistance, and critical force for cracking can be accurately measured. Operation o f the Nano-Indenter is described in detail. A scanning probe microscope (SPM) is shown to be a valuable supplement to the Nano-Indenter. Well-characterized thermoset acrylic clearcoats and thermoplastic latex films were studied. For the first time, operating parameters are described for measurement o f relatively soft coatings, such as films cast from a latex with a glass transition temperature (T5) of 8 deg C. Thus, the method is made available for study of most types of coatings. The method can easily discriminate between coatings with different Ts and crosslink densities. Once operating parameters are established, it takes about 10 minutes for an indentation test and 10 minutes for a scratch test with the Nano-Indenter, and with further automation this time could be reduced. Each indentation test accurately measures hardness and elastic modulus as a function of depth within the coating, and each scratch test provides additional insight into the material's behavior. The method is sensitive to small changes in polymer composition and formulation, and results are highly reproducible. Two groups of specimens were studied in the present work: three clearcoat thermoset enamel films and two unpigmented thermoplastic films derived from acrylic latexes. Latex films were cast on aluminum panels.