CoCrFeNi High-Entropy Alloy Thin Films Synthesised by Magnetron Sputter Deposition from Spark Plasma Sintered Targets

Holger Schwarz,Olav Hellwig,Thomas Lindner,Thomas Seyller,Thomas Uhlig,Fabian Ganss,Guntram Wagner,Niels Rösch,Thomas Lampke

doi:10.3390/coatings11040468

Holger Schwarz, Olav Hellwig + Show 7 more

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https://doi.org/10.3390/coatings11040468

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Abstract

Two magnetron sputter targets of CoCrFeNi High-Entropy Alloy (HEA), both in equal atomic ratio, were prepared by spark plasma sintering. One of the targets was fabricated from a homogeneous HEA powder produced via gas atomisation; for the second target, a mixture of pure element powders was used. Economic benefits can be achieved by mixing pure powders in the intended ratio in comparison to the gas atomisation of the specific alloy composition. In this work, thin films deposited via magnetron sputtering from both targets are analysed. The surface elemental composition is investigated by X-ray photoelectron spectroscopy, whereas the bulk stoichiometry is measured by X-ray fluorescence spectroscopy. Phase information and surface microstructure are investigated using X-ray diffraction and scanning electron microscopy, respectively. It is demonstrated that the stoichiometry, phase composition and microscopic structure of the as-deposited HEA thin films are almost identical if the same deposition parameters are used.

Highlights

While all four of the expected High-Entropy Alloy (HEA) elements can be identified in the spectra of the pristine targets, it can be seen that the surface shows significant contamination with oxygen and carbon
The 2p core levels of the involved HEA elements Co, Cr, Fe and Ni were measured with higher resolution
It can be said that the thin films prepared by magnetron sputtering from the two sputter targets presented in this work are very similar regarding their investigated properties

Summary

Introduction

Complex alloys were defined and reported for the first time by Cantor et al [1] and are often referred to as High-Entropy Alloys (HEAs) [2,3] In this class of materials, an equimolar or near-equimolar mixture of four or more elements is created, in contrast to common alloys, with one primary element, e.g., steels [1]. It is predicted that the high configurational entropy and low mixing enthalpy of such a compound will lead to a preferential formation of single-phase solid solutions [2]. Extensive research on this new class of materials revealed numerous remarkable properties, like high wear resistance [4], high corrosion resistance [5], or high hardness [6,7]. HEAs have already been successfully sputtered from mosaic targets [8,9], loosely pressed powder targets [10,11,12] or sintered targets [13,14,15]

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