Characterisation of HIPIMS deposited Cr2N and CrN coatings

CrNx coatings have been grown with varying deposition parameters utilising HIPIMS techniques. In general the pulsing generator was powered with 5.5 kW DC. The pulse duration amounted to 150 µsec and the pulse repeat frequency to 75 Hz. The deposition rates observed depended strongly on the discharge geometry. Under static conditions, a target to substrate distance of 55 mm and B// field of 41 kA/m the rate reached a value of 68 nm/min. Using the appropriate nitrogen flow during static reactive deposition the coatings grown showed single phase hexagonal wurtzite structure for Cr2N and fcc NaCl structure for CrN. CrN showed a strongly{200} preferred orientation. EPMA analyses showed a typical Cr/N ratio coefficient of 2 for Cr2N and 1 to 1.1 for CrN, the latter confirming the well known fact, that complete stoichiometry is hardly to achieve. The hardness of the subnitride showed higher values than the quasi-stoichiometric CrN phase, namely HUplast ~ 40 GPa compared to 31 GPa. CrN coatings exhibited excellent results in both abrasive (< 6·10-15 m³/Nm) and sliding wear (0.5·10-15 m³/Nm) tests, whereas Cr2N exhibits extremely positive results in sliding wear (0.08·10-15 m³/Nm) and negative results in abrasive wear (up to 40·10-15 m³/Nm). CrN outperforms clearly Cr2N in impact testing. Both coatings show identical friction coefficients of 0.4.