Effect of nitrogen addition on the structural, mechanical and corrosion properties of FeCoCrMnNiNx high-entropy nitride ceramic thin films

Abstract

FeCoCrMnNiNx high entropy nitride ceramics thin films were prepared using the magnetron sputtering method, and the effects of nitrogen content on the thin films’ properties were later examined. The addition of N2 affected the microstructures of the thin films and their mechanical and corrosion properties. Compared with the FeCoCrMnNi thin films with 1-sccm N2, the addition of 2 and 3 sccm of N2 by as much as 5.45at% and 6.34at% changed the solid solution’s crystalline structure into an amorphous structure. The addition of nitrogen caused drastic changes to the surface morphology, creating a smoother and more uniform surface without cauliflower units. The atomic force microscopy image analysis indicated that the addition of nitrogen reduced the surface roughness from 5.58 to 1.82 nm. Adding N2 to the CoCrFeMnNi thin film helped increase its mechanical properties, such as hardness and strength, while the Young’s modulus decreased. The hardness of (8.75 ± 0.5) GPa and the reduced Young’s modulus of (257.37 ± 11.4) GPa of the FeCoCrMnNi thin film reached (12.67 ± 1.2) and (194.39 ± 12.4) GPa, respectively, with 1 sccm N2. The applied coating of the CoCrFeMnNi thin film on 304SUS increased the corrosion resistance, whereas the addition of nitrogen to the CoCrFeMnNi thin film also improved its corrosion resistance compared with that of the CoCrFeMnNi thin film without nitrogen.

1. Introduction

For the first time in 1995 [1], research was conducted to produce alloys with unique mechanical, chemical, and physical properties. These alloys could combine several main elements to help produce high-entropy alloys (HEAs) [1–2]. These alloys can be produced with the structure of one or several solid solutions composed of 5–13 elements with chemical combinations of 5–35 atomic percent (at%). HEAs have unique characteristics, such as their high mechanical properties, corrosion and oxidation resistance, abrasion resistance, and high fatigue [1–3]. These alloys are widely used in shafts, bearings, traction device connections, and portable gadgets such as microelectromechanical systems [4–7].

HEAs are manufactured using various methods and for different purposes and are thus prepared in different forms (e.g., powder, bulk, coating, and thin films). These methods include powder metallurgy, casting, and coating [8–10]. For instance, Zhang et al. [11] used the casting method to produce HEAs of CoCrFeMnNi in 2015, which had a tensile strength of 1 GPa, an elongation of around 70%, and a high toughness of 4200 MPa·m1/2. In 2023, Feng et al. [12] produced bulk nitride ceramics of CoCrFeMnNi using induction furnace casting and investigated the effects of nitrogen on the Charpy impact energy of the high-entropy bulk alloy of CoCrFeMnNi. They concluded that nitrogen atoms fully dissolved in the alloy structure and significantly increased the Charpy impact energy of the CoCrFeMnNi alloy [12].

Methods of coating and creating thin films of HEAs include direct current magnetron sputtering [13], pulse laser deposition [14–15], pulse electroplating [16], and spraying methods [17]. Direct current magnetic sputtering and radio frequency sputtering are the main methods of producing thin films of HEAs [18–20]. In 2018, Dang et al. [21] deposited a high-entropy coating of CoCrFeMnNi using radio frequency sputtering with 300-nm-thick films, suggesting that the said coating had body center cubic (BCC) and face center cubic (FCC) structures with a hardness of around 6.8 GPa and a Young’s modulus of almost 180 GPa.