Influence of Si content on cracking behavior of CrAlSiN coatings

Physical Vapor Deposition (PVD) manufactured CrAlSiN nanocomposite coatings, composed of CrAlN grains in a SiN x matrix, represent a promising solution for improved cutting performance of milling tools. The elastic-plastic properties and deformation behavior of the material composite thereby can be deliberately influenced by varying the silicon content. CrAlSiN coatings with silicon contents of x S i = 10, 16, 22, and 29 at.-% in the metal portion were fabricated on cemented carbide WC-Co substrates. The indentation hardness H IT and modulus E IT of the coatings were measured through nanoindentation, using a Berkovich indenter. Additionally, crack resistance was evaluated using high load (HL) nanoindentation tests under forces ranging from F HL = 750 to 1750 mN, using a conical diamond indenter. The findings reveal that the indentation hardness H IT remains unchanged at H IT = (25.5 ± 1.6) GPa, while the indentation modulus increases with higher silicon content. After high load nanoindentation all coatings exhibit no cracks at F HL = 750 mN. Initial cracks are observed at F HL = 1000 mN for x Si = 10 at.-%, whereas they appear at just F HL = 800 mN for x Si = 29 at.-%. With a further increase in load to F HL = 1750 mN, it is evident that the coating with a silicon content of x Si = 22 at.-% displays the fewest and shortest cracks. Coatings with high silicon content therefore demonstrate promising crack resistance at room temperature even though the examination of indentation hardness and modulus does not support this behavior at first sight. This highlights their potential for further investigation, qualifying these coatings for additional studies under high-temperature conditions, aiming to enhance their applicability in machining processes.