Improvement of discharge and microstructure of Cr-C-N coatings by electromagnetically enhanced magnetron sputtering

The Cr-C-N coatings were deposited on M2 high-speed steel (HSS) and Si (100) wafer using conventional magnetron sputtering (CMS) and electromagnetically enhanced magnetron sputtering (EMEMS) techniques. Different external magnetic field strength was generated by varying the electromagnetic coil current from 0 to 90 A. The substrate current density (J) was measured and the microstructure and hardness of the Cr-C-N coatings was investigated by field-emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and micro-hardness tester. The results showed that the J increased by a factor of more than 2 with the assistance of a coil current of 90 A, indicating a significantly enhanced glow discharge. The Cr-C-N coatings showed dense columnar grain structure. All coatings exhibited a granular surface morphology with a decrease in the granular size as the coil current increased. The structural improvement was attributed to the enhanced ion bombardment from the increased ion flux generated by the EMEMS technique. By increasing the coil current above 30 A, Cr-C-N coatings exhibited smaller intensity ratio of the D-Raman peak and the G-Raman peak (ID/IG), which indicated higher sp3 contents in the coatings. The maximum microhardness (approximately HV 1560) of the coating was obtained at a coil current of 90 A.