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A comparative study of adhesion test methods for hard coatings

: Ollendorf, H.; Schneider, D.


Surface and coatings technology 113 (1999), S.86-102
ISSN: 0257-8972
Fraunhofer IWS ()
Laser-Akustik; Verformung; Festigkeit; Ultraschall

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 studies were performed with TiN films of thickness from 1.2 to 2.4 5m deposited on 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 deposition. Argon pre-sputtering for 15 minutes is recommended to guarantee an optimal adhesion. The pre-sputtering time tS was reduced down to 0.5 minutes 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, Young's modulus of the film measured with the laser-acoustic method. It was investigated, if these test parameters correlate with the pre-sputtering time tS. The results are summarized in a table that shows which test methods and test parameters yield corresponding and contradictory evaluations of the film quality. The effect of defect density and residual stresses is discussed. Laser-acoustics and acoustic microscopy are non-destructive methods. Young's modulus measured by laser-acoustics is sensitive to the density of micro-defects. It is expected to indicate their effect on the adhesion.