CONTINUOUS MICROSCRATCH MEASUREMENTS OF THIN-FILM ADHESION STRENGTHS

The adhesion strengths of metal/ceramic, metal/polymer, and polymer/po lymer interfaces have been characterized using the continuous microscr atch technique. In these experiments, a conical diamond indenter was d riven simultaneously into a thin film at a rate of 15 nm/s and across the film surface at a rate of 0.5 mu m/s until a load drop or other di scontinuity occurred, indicating film failure. The critical load at fa ilure of the thin film was taken as a measure of the adhesion strength . For metal/ceramic systems such as Cr thin films on Al2O3, and for di amond-like-carbon (DLC) films on glass, clear load drops provided an a ccurate measure of the adhesion strengths. For metal/polymer systems s uch as Cu thin films on PET, a change in the loading pattern and perio dic cracking events along the scratch track provided evidence of film delamination. For DLC films on polycarbonate substrates, the carbon th in film cracked before it delaminated. For bulk polymers such as polyc arbonate and polystyrene/polypropylene, crack growth occurred by a sti ck-slip mechanism. Using a model developed in an earlier paper, the pr actical work of adhesion for the Cr/Al2O3 system was determined to be 0.09 J/m(2) and that for the DLC/polycarbonate system was 0.05 J/m(2). The fracture toughnesses of the polycarbonate and polystyrene were 0. 81 and 0.2 MPa m(1/2), respectively. These numbers are in good agreeme nt with those obtained by other methods for these systems.