Synthesis of High-Entropy Alloys with a Tailored Composition and Phase Structure Using a Single Configurable Target

Khurshed Alam; Woohyung Jang; Geonwoo Jeong; Jinhui Ser; Doori Kang; Tae-Hoon Kim; Hoonsung Cho

doi:10.1021/acsomega.3c07721

Synthesis of High-Entropy Alloys with a Tailored Composition and Phase Structure Using a Single Configurable Target

ACS Omega. 2023 Dec 26;9(1):1362-1374. doi: 10.1021/acsomega.3c07721. eCollection 2024 Jan 9.

Authors

Khurshed Alam^{1

2}, Woohyung Jang³, Geonwoo Jeong¹, Jinhui Ser^{1

4}, Doori Kang¹, Tae-Hoon Kim¹, Hoonsung Cho¹

Affiliations

¹ School of Materials Science & Engineering, Chonnam National University, Gwangju 61186, Republic of Korea.
² Department of Metal Powder, Korea Institute of Materials Science, 51508 Changwon, South Korea.
³ Department of Prosthodontics, School of Dentistry, Chonnam National University, Gwangju 61186, Korea.
⁴ Gordon Center for Medical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, United States.

Abstract

Previously, refractory high-entropy alloys (HEAs) with high crystallinity were synthesized using a configurable target without heat treatment. This study builds upon prior investigations to develop nonrefractory elemental HEAs with low crystallinity using a novel target system. Different targets with various elemental compositions, i.e., Co₂₀Cr₂₀Ni₂₀Mn₂₀Mo₂₀ (target 1), Co₃₀Cr₁₅Ni₂₅Mn₁₅Mo₁₅ (target 2), and Co₁₅Cr₂₅Cu₂₀Mn₂₀Ni₂₀ (target 3), are designed to modify the phase structure. The elemental composition is varied to ensure face-centered cubic (FCC) or body-centered cubic (BCC) phase stabilization. In target 1, the FCC and BCC phases coexist, whereas targets 2 and 3 are characterized by a single FCC phase. Thin films based on targets 1 and 2 exhibit crystalline phases followed by annealing, as indicated by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. In contrast, target 3 yields crystalline thin films without any heat treatment. The thin-film coatings are classified based on the atomic size difference (δ). The δ value for the target with the elemental composition CoCrMoMnNi is 9.7, i.e., ≥6.6, corresponding to an HEA with an amorphous phase. However, the annealed thin film is considered a multiprincipal elemental alloy. In contrast, δ for the CoCrCuMnNi HEA is 5, i.e., ≤6.6, upon the substitution of Mo with Cu, and a solid solution phase is formed without any heat treatment. Thus, the degree of crystallinity can be controlled through heat treatment and the manipulation of δ in the absence of heat treatment. The XRD results clarify the crystallinity and phase structure, indicating the presence of FCC or a combination of FCC and BCC phases. The outcomes are consistent with those obtained through the analysis of the valence electron concentration based on X-ray photoelectron spectroscopy. Furthermore, a selected area electron diffraction analysis confirms the presence of both amorphous and crystalline structures in the HEA thin films. Additionally, phase evolution and segregation are observed at 500 °C.