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

Abstract

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 test 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 × 10−7 mm3/Nm, which was two orders of magnitude lower than pure MoS2 (5.66 × 10−5 mm3/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.