Microstructure and phase forming behaviour of chrome based multi-composition nitride coatings with nanolayer structures

Nanoscale multilayer Cr-Nb-N hard coatings were fabricated by reactive hybrid physical vapour deposition (PVD), which was combined with arc ion plating (AIP) for depositing chromium (Cr) and an unbalanced magnetron (UBM) DC sputter for depositing niobium (Nb) on a steel substrate under a controlled gas mixture of Ar and N2. The phase evolution and microstructure of the coatings were analysed by X-ray diffractometer (XRD), field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The formation behaviour of the multilayer structure of the coatings was changed using different rotation conditions for the substrate. The Cr-Nb-N coatings, which formed at a substrate rotation of 5 or 6 rpm, exhibited modulation of the peaks approximately 36°, (111) plane, which indicated the formation of a superlattice in the XRD results. The superlattice structured Cr-Nb-N coating formed under the 5 rpm rotation condition exhibits a large layer period (~25 nm) and improved hardness (~35 GPa) compared to other multilayer Cr-Nb-N or monolithic CrN coatings.