A Comparative Study Of Crn_x Coatings Synthesized By Dc And Pulsed Dc Magnetron Sputtering

摘要

Chromium nitride (CrN_x) coatings were prepared by reactively sputtering chromium metal target with various nitrogen flow rate percentages (f_(N2)) using a closed field unbalanced magnetron sputtering system operated in dc and middle frequency pulsed condition (100 kHz and 50% duty cycle). In this study, plasma examination proved that a large amount of ions with a wide range of ion energies (up to 65 eV and mainly from 10-30 eV region) was identified in the pulsed plasma compared to the low ion flux and energy (0-10 eV) in a dc discharged plasma. The results showed that the phase structure of CrN_x coatings was changed from nitrogen doped Cr(N) to pure β-VCr_2N, and to a mixture of β-Cr_2N and c-CrN and then to pure c-CrN phases with an increase in the f_(N2) in both dc and pulsed conditions. However, the pulsed CrN_x coatings exhibit lower N concentrations than dc CrN_x coatings prepared under the same f_(N2), which leads to the existing of β-Cr_2N phase within a wide range of f_(N2) (30-50%). In comparison with the typical large columnar structure in the dc sputtered coatings, the pulsed CrN_x coatings exhibit dramatic microstructure improvements which benefited from the improved plasma density and ion bombardment from the pulsed plasma, where the super dense and nearly equi-axial structures were observed in a wide range of f_(N2). The microstructure improvements contributed to the enhancements in the hardness and wear resistance of pulsed CrN_x coatings. In the pulsed CrN_x coatings, the hardness values were above 30 GPa when the f_(N2) is in the range of 30-40%, which is related to the formation of the β-Cr_2N phase. With the formation of a mixture of β-Cr_2N and c-CrN phases in the coatings deposited with 40-50% f_(N2), a low COF of 0.36 and wear rate of 1.66× 10~(-6) mm~3N~(-1) m~(-1) can be achieved.