Modeling of cracking behavior of CrAlN coatings on silicon during micro- and nanoindentation

The deformation and failure behavior of any coating governs the performance of the resulting coating system. In the present work, we numerically and experimentally examine the fundamental deformation mechanisms of CrAlN coating on Si substrate, particularly its cracking behavior under indentation processes. For this purpose, CrAlN coatings deposited on monocrystalline Si substrates by pulsed DC magnetron sputtering were subject to indentation procedures with different depths. Subsequent characterization of top surface and cross-sectional morphologies demonstrates a strong dependence of coating profile and microstructures on the initial surface condition of the substrate. Specifically, uniform CrAlN coatings with a thickness of 1.1 μm and densified columnar microstructures were prepared on a polished Si substrate. Berkovich nanoindentation test with an indentation depth of 530 nm derives the mechanical properties of the prepared CrAlN coating. The corresponding finite element simulation reveals the propensity of cracking initiation accompanied by the stress concentration at three edge corners of the dent. Subsequent microindentation test with an indentation depth of 1.09 μm demonstrates the coexistence of plastic deformation and brittle fracture of CrAlN coating. In particular, surface radial cracks within CrAlN coating are experimentally and theoretically observed, and the cracking processes are analyzed in detail by finite element simulations.