Reduction of the coefficient of friction of niobium nitride coatings by the addition of bismuth

• Published in: Vacuum Vol. 125; pp. 146 - 153
• Main Authors: Mirabal-Rojas, Roberto, Depablos-Rivera, Osmary, Gómez, Celia L., Fonseca-Garcia, Abril, Medina, Juan C., Barrera-Ortega, Cecilia C., Pérez-Alvarez, Jonatan, Muhl, Stephen, Camps, Enrique, Rodil, Sandra E.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-03-2016
• Subjects: Coatings; Coefficient of friction; Deposition; Hard coatings; Hardness; Magnetron sputtering; Mechanical properties; Niobium; Niobium nitride; Reduction; Thin films; Thin films; Mechanical properties; Magnetron sputtering; Hard coatings
• ISSN: 0042-207X; 1879-2715
• DOI: 10.1016/j.vacuum.2015.12.016

Composite coatings of niobium nitride containing bismuth inclusions were deposited using a dual magnetron sputtering system with independent power suppliers for each targets; Bi and Nb. The deposition was performed under and Ar/N2 atmosphere at a 2.3 flow rate ratio, which allows the stoichiometric NbN phase to be obtained. The aim of this work was to evaluate the effect of increasing concentrations of Bi, proposed as a lubricous second phase, in the structural, mechanical and tribological properties of niobium nitride (NbN) coatings, searching for a reduction in the coefficient of friction but trying to keep hardness values larger than the tool steels (>10 GPa). The power applied to the Nb target was fixed, while the power on the Bi target was increased; obtaining Bi atomic percentage values of 1.7, 4.9 and 8.4 at%. The Bi inclusions showed different sizes and distribution in the volume and surface of the coatings. The results indicated a reduction in the hardness from 30 GPa of the NbN coating to 13.9 GPa for the highest Bi concentration. However, a more significant reduction was observed for the coefficient of friction (CoF) from 0.8 of the NbN to 0.3 for Bi concentrations between 4.9 and 8.4 at%.
•Bismuth decreases the friction coefficient of Niobium Nitride by 66 percentages.•Bismuth decrease the hardness of Niobium Nitride between 23 and 54%.•The optimal percentage of bismuth inclusions is 4.9 atomic percentages.•The Elastic Modules of the Niobium nitride decrease between 23 and 35 percentages.