A comparative study of adhesion test methods for hard coatings

摘要

The feasibility of seven techniques for testing and evaluating the adhesion of thin films was investigated: scratch test, four-point. bending test, Rockwell test, cavitation test, impact test, laser-acoustics and acoustic microscopy. The studieswere performed with. TiN films (thickness 1.2-2.45μm) deposited on the annealed steel 42CrMo4. The adhesion of the TiN films was varied by varying the time of pre-sputtering the steel substrate with argon ions before the film dep6sition. Argonpre-sputtering for 15 min is recommended to guarantee an optimal adhesion. The pre-sputtering time, t{sub}s, was reduced down to 0.5 min to reduce the adhesion. The following test parameters were used to evaluate ,the adhesion: the friction work, acoustic emission activity and critical load of the scratch test, the critical Strain and the defect density of the four-point bending test, the proportional damage area of cavitation test, the critical number of loading cycles of the impact test, and Young'smodulus of the film measured with the laser-acoustic method. These test parameters were examined for any correlation with the pre-sputtering time, t{sub}s The results are summarized in a table that shows which test methods and test parameters yieldcorresponding and contradictory evaluations of the film quality. The effect of defect density and residual stresses is discussed. Laser-acoustics and acoustic microscopy are nondestructive methods. Young's modulus, as measured by laser-acoustics, issensitive to the density of micro-defects. This is expected to indicate their effect on the adhesion.