Microstructure, Hardness, and Elastic Modulus of a Multibeam-Sputtered Nanocrystalline Co-Cr-Fe-Ni Compositional Complex Alloy Film

Péter Nagy,Zoltán Hegedűs,László Pethö,Nadia Rohbeck,Johann Michler,János L Lábár,Jenő Gubicza

doi:10.3390/ma14123357

Abstract

A nanocrystalline Co-Cr-Ni-Fe compositional complex alloy (CCA) film with a thickness of about 1 micron was produced by a multiple-beam-sputtering physical vapor deposition (PVD) technique. The main advantage of this novel method is that it does not require alloy targets, but rather uses commercially pure metal sources. Another benefit of the application of this technique is that it produces compositional gradient samples on a disk surface with a wide range of elemental concentrations, enabling combinatorial analysis of CCA films. In this study, the variation of the phase composition, the microstructure (crystallite size and defect density), and the mechanical performance (hardness and elastic modulus) as a function of the chemical composition was studied in a combinatorial Co-Cr-Ni-Fe thin film sample that was produced on a surface of a disk with a diameter of about 10 cm. The spatial variation of the crystallite size and the density of lattice defects (e.g., dislocations and twin faults) were investigated by X-ray diffraction line profile analysis performed on the patterns taken by synchrotron radiation. The hardness and the elastic modulus were measured by the nanoindentation technique. It was found that a single-phase face-centered cubic (fcc) structure was formed for a wide range of chemical compositions. The microstructure was nanocrystalline with a crystallite size of 10–27 nm and contained a high lattice defect density. The hardness and the elastic modulus values measured for very different compositions were in the ranges of 8.4–11.8 and 182–239 GPa, respectively.

Highlights

High-entropy alloys (HEAs) are in the focus of materials science
Previous phase diagram calculations revealed that in the Co-Cr-Ni-Fe system, when all constituent element concentrations were between 20 and 40 at.%, a single-phase fcc structure formed at room temperature (RT) [25]
Since the present physical vapor deposition (PVD) processing was performed at RT, we tried to estimate the equilibrium phase composition from the room temperature ternary phase diagrams for the studied points where one or two components had relatively low concentrations

Summary

Introduction

High-entropy alloys (HEAs) are in the focus of materials science. HEAs are equimolar or near-equimolar alloys formed from five or more elements that display high mixing entropy [1,2]. The manufacturing of HEA thin films utilizes many methods and techniques, such as direct-current magnetron sputtering [7,8], thermal evaporation [9], radio-frequency sputtering [10], or multibeam sputtering [11]. In the work of Dolique et al, it was shown that in the case of a magnetron-sputtered Al-Co-Cr-Cu-Fe-Ni HEA thin-film sample, even a small difference in the stoichiometry could lead to a different structure and thermal stability [13]. In the case of an Al-Co-Cr-Cu0.5 -Fe-Ni thin film deposited by radio-frequency magnetron sputtering, it was shown how the sputtering condition could be used to tailor the microstructure and the chemical composition of the sample [10]

Methods

Results

Discussion

Conclusion