Adhesion strength evaluation of diamond-like carbon coatings via acoustic emission and characterization of delamination modes using fast fourier transform analysis

Diamond-like carbon (DLC) coatings exhibit high hardness and low friction coefficient, making them effective in reducing friction under lubricated conditions. As their application to engine components expands, reliable evaluation of adhesion strength becomes increasingly important. This study proposes an acoustic emission (AE)-based method for assessing the adhesion strength of DLC coatings by analyzing signals generated during delamination. The critical contact pressure at which AE signals first appear was identified as an indicator of delamination onset. FFT-based AE analysis was also employed to characterize failure conditions. Along these lines, we conducted friction tests using ta-C films with different delamination modes, and AE signal parameters—including event count, amplitude, frequency, and energy—were analyzed. The results revealed significant differences in AE behavior depending on the delamination mode. Statistical evaluation confirmed adhesion strength hierarchy (ta-C(A) < ta-C(B) < Ni/ta-C(C), p < 0.001), and a reduction in coefficient of variation from 43 % to 30 %, indicating a ∼30 % improvement in reproducibility. These findings demonstrate that AE signal analysis not only captures delamination progression but also provides a quantitative index for evaluating coating reliability. • AE+FFT non-destructively distinguish interfacial vs surface-origin modes. • Halted tests with time-resolved AE energy verify initiation→propagation. • ANOVA with Tukey and effect sizes quantify adhesion-strength hierarchy. • Systematic linkage between morphology and frequency-domain signatures. • Generalizable workflow for mode identification under lubricated sliding.