Welding Techniques for High Entropy Alloys: Processes, Properties, Characterization, and Challenges

Abstract

High entropy alloys (HEAs) are the outstanding innovations in materials science and engineering in the early 21st century. HEAs consist of multiple elements with equiatomic or near equiatomic compositions, which exhibit superior mechanical properties, such as wear resistance, fatigue resistance, and corrosion resistance. HEAs are primarily used in structural and functional applications; hence, appropriate welding processes are essential to enhancing the performances and service lives of HEA components. Herein, a comprehensive overview of current state-of-art-of welding techniques for HEAs is elucidated. More specifically, the article discusses the fusion-based welding techniques, such as gas tungsten arc welding (GTAW) and laser beam welding (LBW), and solid-state welding techniques, such as friction stir welding (FSW) and explosive welding (EB), for a broad category of HEAs. In addition, the microstructural features and mechanical properties of HEAs welded using different techniques were explained for a broad spectrum of HEAs. Finally, this review discusses potential challenges in the welding of HEAs.

Keywords: fusion welding; high entropy alloys; mechanical properties; microstructure; solid-state welding; welding.

Figure 1

The number of published articles on “Welding of HEAs, 2016 to 2021 from the Web of Science.

Figure 2

Welding techniques for HEAs.

Figure 3

EBSD analysis of the CrMnFeCoNi HEA weld joint: (A) the fusion line, (B) the HAZ, (C) the HAZ containing twins, (D) the BM. Reproduced with permission from [78]. Copyright Elsevier, 2020.

Figure 4

EBSD of (a) BM, (b) HAZ and WM of HEA fillers, (c) HAZ and WM of STS 308 L, (d) center of WM of HEA fillers, (e) center of WM of STS 308 L. Reproduced with permission from [80]. Copyright Elsevier, 2020.

Figure 5

Microhardness distribution across the GTAWed HEA corresponding to STS 308 L and HEA fillers. Reproduced with permission from [80]. Copyright Elsevier, 2020.

Figure 6

Macrogrpahs of the weld beads for various welding velocities: (a) 6 m/min, (b) 8 m/min, and (c) 10 m/min. Reproduced with permission from [71]. Copyright Elsevier, 2019.

Figure 7

(a) Macrograph of weldment corresponding to 5 mm/min, (b) variation of fusion zone width with welding speed. Reproduced with permission from [73]. Copyright Elsevier, 2019.

Figure 8

Fatigue test results of LBWed CoCrFeNiMn HEA and BM. Reproduced with permission from [72]. Copyright Elsevier, 2019.

Figure 9

SEM/EDS analysis of (a) as-weld, and PWHTed joint (b) 800 °C (c) 1000 °C. Reproduced with permission from [88]. Copyright Elsevier, 2021.

Figure 10

Variation in microhardness of the as -weld is shown in the black line, PWHT at 800 °C indicated in red line or PWHT at 1000 °C is shown in the blue line. Reproduced with permission from [88]. Copyright Elsevier, 2021.

Figure 11

Schematic of FSW process. Reproduced with permission from [95]. Copyright Elsevier, 2005.

Figure 12

Various zones in the FSW process. Zone A is SZ, zone B is TMAZ, zone C is HAZ and D is BM. Reprinted with permission from reference [93]. Copyright MDPI, 2021.

Figure 13

Macrostructure of the weld joint after welding at (a) 30 mm/min, (b) 50 mm/min Reproduced with permission from [100], Copyright Elsevier, 2018.

Figure 14

Tensile properties of the FSWed HEA (a) stress-strain curve, (b) UTS and YS of the joints (c) tensile specimen. Reproduced with permission from [101], Copyright Elsevier, 2019.

Figure 15

Schematic of the EW technique.

Figure 16

Hardness distribution at the interface of HEA and pure copper. Reproduced with permission from [111]. Copyright MDPI, 2021.

Figure 17

EW of HEA and aluminum: (a) optical image, (b) stand-off distance: 3 mm, (c) stand-off distance 2: mm, (d) stand-off distance: 1 mm. Reproduced with permission from [112]. Copyright Elsevier, 2020.