Mechanical and tribological properties of multicomponent Ti-B-C-N thin films with varied C contents

Multicomponent thin films of Ti-B-C-N with different C contents (C target current ranging from 0.0 to 4.0 A) were deposited onto unheated Si(100) wafers (for mechanical analyses) and M42 tool steels (for tribological measurements) by reactive close-field unbalanced dc-magnetron sputtering in an Ar-N₂ gas mixture. These films were characterized and analyzed in terms of their microstructure by X-ray diffraction, their hardness by microindentation measurements, their surface root-mean-square roughness by atomic force microscopy, and their friction and wear behaviors by Rockwell-C testing, microscratch testing, dynamic impact testing and pin-on-disc tribometer. It was found that the mechanical and tribological properties of multicomponent films (typically 1.6 ± 0.2 μm in thickness) were closely related to the C content (varied from 4.4 at.% to 42.0 at.%). For the best multicomponent film with 12.4 at.% C content, a high hardness of 27 GPa was achieved and the best cohesive and adhesive strength was evidenced in terms of critical load values of L_C1 (~ 37 N), L_C2 (>75 N), and the highest adhesive strength (HF1). Moreover, by dynamic impact testing the multicomponent film could endure impact cycles up to 2 × 10⁵ without adhesive failure. However, when the C content was further increased up to 42.0 at.%, the hardness, cohesive and adhesive strength were decreased due to the formation of amorphous structure. It was also found that the pin-on-disc test under dry conditions showed that the frictional coefficients decreased with C content. The frictional coefficients obtained at a load of 2 N were kept at ∼0.57 without C incorporation and decreased to ~0.18 at C current of 4.0 A. The tribological properties of the Ti-B-C-N films with different C contents are also explained in terms of mechanical properties and wear mechanisms.