Enhancing the wear resistance of magnetron sputtered VN coating by Si addition

• Nanocomposite structure and enhanced mechanical properties of VSiN coatings.
• Improvement on the wear resistance of VN coatings by Si addition.
• To compare the wear mechanism of coatings under low and high hertzian pressures.
• To discuss the main causes of mild wear for transition-metal nitride coatings.

Although Si addition into transition metal nitrides has been long known to enhance hardness of coatings, relatively less evidence indicates that the hardness gain can be translated into a significant improvement of wear resistance as expected. The reported wear rates of TM–Si–N coatings are generally greater than 10−16 m3/N m. Here, we prepared VSiN coatings by adding Si into VN coatings, and investigated the friction-wear behavior of the VSiN coatings which achieved wear rates on the 10−17 m3/N m order of magnitude. The friction-wear behavior was studied by ball-on-plate sliding tests against Al2O3 balls (3 or 6 mm in diameter), followed by microscopic examination on the worn surfaces. For the VN coating mild wear transited to fatigue failure after ~104 sliding cycles with crack growth and propagation, whereas the VSiN coatings retained mild wear more than 105 cycles, in which the sliding wear proceeded predominately by tribo-oxidation removal mechanism. The enhanced wear resistance of the VSiN could be mainly attributed to their special nanocomposite structure that limited intergranular cracks, and then suppressed fracture-dominated wear. Based on the results, it was proposed that the resistance to fracture-dominated wear could be taken into account for developing low-wear transition-metal nitride coatings.