Nanomechanical and Nanotribological Properties of Nanostructured Coatings of Tantalum and Its Compounds on Steel Substrates.

Galina Melnikova,Evgeniy Sadyrin,Stanislav Yakovin,Agata Petrovskaya,Sergei Aizikovich,Tatyana Kuznetsova,Anna Zykova,Sergei Chizhik,Vladimir Safonov,Weifu Sun,Vasilina Lapitskaya

doi:10.3390/nano11092407

Abstract

The present paper addresses the problem of identification of microstructural, nanomechanical, and tribological properties of thin films of tantalum (Ta) and its compounds deposited on stainless steel substrates by direct current magnetron sputtering. The compositions of the obtained nanostructured films were determined by energy dispersive spectroscopy. Surface morphology was investigated using atomic force microscopy (AFM). The coatings were found to be homogeneous and have low roughness values (<10 nm). The values of microhardness and elastic modulus were obtained by means of nanoindentation. Elastic modulus values for all the coatings remained unchanged with different atomic percentage of tantalum in the films. The values of microhardness of the tantalum films were increased after incorporation of the oxygen and nitrogen atoms into the crystal lattice of the coatings. The coefficient of friction, CoF, was determined by the AFM method in the “sliding” and “plowing” modes. Deposition of the coatings on the substrates led to a decrease of CoF for the coating-substrate system compared to the substrates; thus, the final product utilizing such a coating will presumably have a longer service life. The tantalum nitride films were characterized by the smallest values of CoF and specific volumetric wear.

Highlights

IntroductionThe stainless steel (for example, 316L SS), platinum iridium alloys, tantalum, nitinol, cobalt–chrome alloys, titanium and its alloys, and pure iron and magnesium alloys are the basic materials for the production of stents
The coatings of Ta, Ta2 O5, TaN, and TaON were deposited on the polished stainless steel substrates using reactive direct current planar magnetron sputtering
The substrates were placed in a chamber pumped to a residual vacuum of less than 10−3 Pa

Summary

Introduction

The stainless steel (for example, 316L SS), platinum iridium alloys, tantalum, nitinol, cobalt–chrome alloys, titanium and its alloys, and pure iron and magnesium alloys are the basic materials for the production of stents. Stainless steel is the most common material for the production of stents with and without coatings. The stents made of stainless steel demonstrate suitable mechanical properties and excellent corrosion resistance. The clinical application of steel is limited by the ferromagnetic nature of the alloy and its low density. Due to these properties, the steel is poorly visible in X-ray and magnetic resonance

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