Structure and properties of Ti–B–C–N nanocomposite coatings synthesized using pulsed closed field unbalanced magnetron sputtering (P-CFUBMS)

Ti-B-C and Ti–B–C–N nanocomposite coatings with various nitrogen contents were synthesized by sputtering an 80 mol.%TiB2–20 mol.%TiC compound target in Ar/N2 plasma using a pulsed closed field unbalanced magnetron sputtering (P-CFUBMS) system. It was found that the structure, mechanical and wear properties of Ti–B–C–N coatings exhibit a strong dependence on the nitrogen content. When the nitrogen content is in the low range, e.g. 3 at.%, the Ti–B–C–N coating was characterized as a mixture of Ti(B,C) nanocrystallines and small volume fractions of free carbon, amorphous BN and CNx, where a super hardness of 48.5 GPa has been achieved. When the nitrogen content was increased, e.g. 10–13 at.%, the reduction of Ti(B, C) phase accompanied with the formation of nanocrystalline Ti(C,N) and amorphous BN phases were observed. The coatings can be characterized as nanocrystalline Ti(B,C) and Ti(C,N) phases imbedded in a amorphous BN, CNx and free carbon matrix, in which a slight decrease in the coating hardness (37–45 GPa), while improvements in the wear resistance were indentified. When the nitrogen content was further increased to high levels, e.g. 36 at.%, a significant increase in the volume fraction of amorphous BN and a decrease in the crystalline phases in the coatings will result in a decrease in both the hardness and the wear resistance.