Duplex processing for increased adhesion of sputter deposited Ti1-xAlxN coatings on a Fe–25%Co–15%Mo tool material

Recently, carbide-free alloying systems with yield strength Rp0.1 of up to 4000 MPa and outstanding thermal stability are available, which offer the possibility to elevate coating deposition temperatures up to 600 °C. The present work demonstrates that the limited Ti1−xAlxN coating adhesion on a Fe–25%Co–15%Mo grade caused by the absence of carbides in the substrates can be significantly improved from HF 4 to HF 2 in the Rockwell adhesion test by plasma-assisted nitriding during sputter etching. X-ray photoelectron spectroscopy measurements reveal that the nitrogen diffusion zone is confined to the first few nanometre of the substrate surface, while mainly Mo–N and partly Fe–N bondings are formed. X-ray diffraction exhibits the formation of cubic Mo2N in the nitrided layer. The coatings show a single-phase face-centered cubic Ti1-xAlxN structure tending to a preferred (110) growth orientation with increasing nitriding time. Tribological tests performed at room temperature and 650 °C indicate superior wear performance of duplex Ti1-xAlxN coated Fe–25%Co–15%Mo.