Effect of boron content on the structure, mechanical and tribological properties of sputtered Mo-S-B films

Molybdenum disulfide (MoS2) is a widely applied solid lubricant due to its unique layered structure. However, low hardness and environmental sensitivity severely limit its practical application in industry. Here, Mo-S-B films were deposited on Si (100) substrates by magnetron sputtering. The structure, mechanical and tribological properties showed a significant dependency on composition and chemical bonding. Increasing the B content from 0 to 23.4 at. %, the surface became smooth, corresponding to a transition from columnar structure to dense feature, along with a phase transition from hexagonal-MoS2 to amorphous phase. The hardness lineally increased from 0.75 GPa for MoS2 to 8.38 GPa for the Mo-S-B film with 23.4 at.% B. The tribological properties of films were evaluated against steel ball using ball-on-disc tribometer. The tribological WA results indicated that the increased B content led to the enhancement of wear resistance for Mo-S-B films, the wear rate of Mo-S-B films with 23.4 at.% B showed the lowest value of 5.5 x 10(-7) mm(3)/Nm, which was two orders of magnitude lower than pure MoS2(5.66 x 10(-5) mm(3)/Nm). The friction coefficient just rose slightly, keeping it at the same level as pure MoS2. Raman analysis for wear debris after rubbing revealed that MoS2 tribofilm improved lubrication behavior.