Characteristics of the Structure, Mechanical, and Tribological Properties of a Mo-Mo2N Nanocomposite Coating Deposited on the Ti6Al4V Alloy by Magnetron Sputtering.

Stanisław Adamiak,Dominik Adamiak,Wojciech Bochnowski,Andrzej Dziedzic,Łukasz Szyller

doi:10.3390/ma14226819

Stanisław Adamiak, Dominik Adamiak + Show 3 more

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https://doi.org/10.3390/ma14226819

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Abstract

Mo-Mo2N nanocomposite coating was produced by reactive magnetron sputtering of a molybdenum target, in the atmosphere, of Ar and N2 gases. Coating was deposited on Ti6Al4V titanium alloy. Presented are the results of analysis of the XRD crystal structure, microscopic SEM, TEM and AFM analysis, measurements of hardness, Young’s modulus, and adhesion. Coating consisted of α-Mo phase, constituting the matrix, and γ-Mo2N reinforcing phase, which had columnar structure. The size of crystallite phases averaged 20.4 nm for the Mo phase and 14.1 nm for the Mo2N phase. Increasing nitrogen flow rate leads to the fragmentation of the columnar grains and increased hardness from 22.3 GPa to 27.5 GPa. The resulting coating has a low Young’s modulus of 230 GPa to 240 GPa. Measurements of hardness and Young’s modulus were carried out using the nanoindentation method. Friction coefficient and tribological wear of the coatings were determined with a tribometer, using the multi-cycle oscillation method. Among tested coatings, the lowest friction coefficient was 0.3 and wear coefficient was 10 × 10−16 m3/N∙m. In addition, this coating has an average surface roughness of RMS < 2.4 nm, determined using AFM tests, as well as a good adhesion to the substrate. The dominant wear mechanism of the Mo-Mo2N coatings was abrasive wear and wear by oxidation. The Mo-Mo2N coating produced in this work is a prospective material for the elements of machines and devices operating in dry friction conditions.

Highlights

Titanium and its alloys are widely used in the aerospace, automotive, chemical, energy, and biomedical engineering industries
The main goal of this work was to obtain a nanocomposite with low friction coefficient and tribological wear, which was formed by nanocrystallites of the Mo matrix and nanocrystallites of the reinforcing phase of the Mo2 N nitride
In order to improve adhesion of the Mo-Mo2 N nanocomposite coating to the substrate, in the first step, a transition layer was created by gradually increasing nitrogen flow rate from 0 to a preset value over a period of 360 s

Summary

Introduction

Titanium and its alloys are widely used in the aerospace, automotive, chemical, energy, and biomedical engineering industries. The decisive factors for the use of titanium alloys are: high specific strength, good fatigue properties, high corrosion resistance, and biocompatibility. The relatively low hardness of titanium, low modulus of longitudinal elasticity, high chemical activity at elevated temperatures, and a tendency to build up and stick to mating surfaces [1,2] mean that titanium and its alloys have only limited uses under tribological wear conditions. The surface modification of titanium alloys is still an active research subject for industrial applications. Technologies for the surface treatment of titanium alloys, which include nitriding, nitrogen ion implantation [3], and physical vapor deposition (PVD) enable the production of metal nitride coatings that exhibit increased tribological resistance [4,5]

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