Hard and crack resistant carbon supersaturated refractory nanostructured multicomponent coatings

S Fritze,E Lewin,L Riekehr,L Von Fieandt,P Malinovskis,U Jansson

doi:10.1038/s41598-018-32932-y

Abstract

The combination of ceramic hardness with high crack resistance is a major challenge in the design of protective thin films. High entropy alloys have shown in earlier studies promising mechanical properties with a potential use as thin film materials. In this study, we show that small amounts of carbon in magnetron-sputtered multicomponent CrNbTaTiW films can lead to a significant increase in hardness. The film properties were strongly dependent on the metal composition and the most promising results were observed for TaW-rich films. They crystallised in a bcc structure with a strong (110) texture and coherent grain boundaries. It was possible to deposit films with 8 at.% C in a supersaturated solid-solution into the bcc structure without carbide formation. A major effect of carbon was a significant grain refinement, reducing the column diameter from approximately 35 to 10 nm. This resulted in an increase in hardness from 14.7 to 19.1 GPa while the reduced E-modulus stayed constant at 322 GPa. The carbon-containing films exhibited extremely little plastic deformation around the indent and no cracks were observed. These results show that supersaturation of carbon into high entropy films can be a promising concept to combine superior hardness with high crack resistance.

Highlights

In 2004 the concept of alloying several principal elements was introduced simultaneously by Yeh et al.[1] as high entropy alloys (HEAs) and by Cantor et al.[2] as multicomponent alloys (MCAs)
The results show that CrNbTaTiW high entropy alloys with an extensive solid solubility on the metal lattice can be synthesised by magnetron sputtering
X-ray diffraction (XRD) results show that all film except one crystallise in a cubic bcc structure

Summary

Introduction

In 2004 the concept of alloying several principal elements was introduced simultaneously by Yeh et al.[1] as high entropy alloys (HEAs) and by Cantor et al.[2] as multicomponent alloys (MCAs). The first approach is based on the observation that p-elements such as carbon can lead to grain refinement in magnetron sputtered films[13]. This is due to the limited solubility of these elements in bcc alloys. The second approach is based on the assumption, that the metals in the alloys can segregate to the surface leading to a similar renucleation step as observed for the p-elements. We have investigated the influence of carbon addition and metal content on the mechanical properties of magnetron-sputtered CrNbTaTiW films. Hardness and ductility measurements were performed to investigate the mechanical properties

Objectives

Results

Discussion

Conclusion