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Crystals
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The Joining of High Entropy Alloys and the Brazing Filler...
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The Joining of High Entropy Alloys and the Brazing Filler Metals Using High Entropy Alloys

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Crystalline Metals and Alloys".

Deadline for manuscript submissions: closed (31 May 2022) | Viewed by 8363

Special Issue Editor

Dr. Jiangtao Xiong

E-Mail Website
Guest Editor
School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an 710129, China
Interests: material characterization; mechanical behavior of materials; materials processing

Special Issue Information

High entropy alloys (HEAs) are composed of five or more major elements in either equal or near-equiatomic proportions. Since HEAs have unique compositions and chemical structures, they possess excellent high temperature mechanical properties, sufficient thermal stability and extraordinary strength-ductility combination, which are potential alternatives for the conventional superalloys in the field of aerospace industry. However, due to the difficulty and high cost of manufacturing large-scale high entropy alloy, the precision bonding forming of multi-stage high entropy alloy has become a key link from theory to practical application. solid-state diffusion bonding (DB) and brazing are widely used to bond the materials owing to its excellent mechanical performance, stable microstructure, and low thermal damage to base materials. However, the nature of HEAs, severe lattice-distortion and sluggish diffusion, remains the challenges in welding of HEAs. How to improve the weldability of high entropy alloy by composition regulation, structure design and surface activation is still an urgent problem. In addition, a new design strategy of high entropy interface and filler metals, improving the role of mixing entropy to inhibit the formation of bulky intermetallic compounds between base metals, are proposed. However, this strategy still lacks systematic and reliable design criteria. In order to address such problem and promote the practical application of HEAs, it is necessary to master a broad spectrum of techniques from traditionally separete branches of research.

This special issue of Crystals is expected to provide a platform to report results in the diffusion and brazing of HEAs with special attention to the joint forming mechanism and mechanical properties. Articles and reviews are also welcome

Potential topics include but are not limited to:

  • Diffusion bonding of high entropy alloy
  • Brazing of high entropy alloy
  • The design of High entropy filler metals
  • The design of High entropy interface

Dr. Jiangtao Xiong
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • high entropy alloy
  • diffusion bonding
  • high entropy filler metals
  • friction welding
  • laser welding
  • high entropy interface

Published Papers (4 papers)

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Research

10 pages, 7429 KiB  
Article
Diffusion Bonding of FGH 98 and CoCrNi-Based Medium-Entropy Alloy: Microstructure Evolution and Mechanical Tests
by Yajie Du, Zhaoxi Li, Jiangtao Xiong, Yipeng Chen, Shiwei Li, Jinglong Li and Jihong Dong
Crystals 2021, 11(10), 1158; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11101158 - 23 Sep 2021
Cited by 5 | Viewed by 1820
Abstract
The superalloy FGH98 was successfully diffusion bonded (DB) with medium-entropy alloy (MEA) Al3Ti3(CrCoNi)94 using pure Ni as the interlayer at a temperature range of 1050–1170 °C for 1 h under 5 MPa. The microstructure and mechanical properties of [...] Read more.
The superalloy FGH98 was successfully diffusion bonded (DB) with medium-entropy alloy (MEA) Al3Ti3(CrCoNi)94 using pure Ni as the interlayer at a temperature range of 1050–1170 °C for 1 h under 5 MPa. The microstructure and mechanical properties of joints were investigated. The diffusion bonding seam was composed of an interlayer zone (IZ) and two diffusion-affected zones (DAZ). The IZ and DAZ beside the FGH98 consisted of cubic Ni3(TiAl)-type γ′ phases due to the diffusion of Ti and Al atoms. Meanwhile, the DAZ adjacent to the MEA consisted of spherical γ′ phases. Both of the γ′ phases with different morphology kept the coherent relationship with the matrix. Moreover, increase of bonding temperature led to the morphology of interlayer γ′ phase to transform from sphere to cube. Due to the strengthening effect of a mass of γ′ phase distributed evenly in IZ and the DAZ beside the FGH98, the microhardness and Young’s modulus of these two zones were higher than that of DAZ near the MEA. The maximum shear strength of DB joint, 592 MPa, was achieved in the joint bonded by 1150 °C, which was the typical ductile fracture feature confirmed by the shear dimples. Full article
(This article belongs to the Special Issue The Joining of High Entropy Alloys and the Brazing Filler Metals Using High Entropy Alloys)
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11 pages, 4652 KiB  
Article
Microstructure and Mechanical Properties of Diffusion-Bonded CoCrNi-Based Medium-Entropy Alloy to DD5 Single-Crystal Superalloy Joint
by Shiwei Li, Xianjun Sun, Yajie Du, Yu Peng, Yipeng Chen, Zhaoxi Li, Jiangtao Xiong and Jinglong Li
Crystals 2021, 11(9), 1127; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11091127 - 16 Sep 2021
Cited by 6 | Viewed by 2046
Abstract
This study focuses on the diffusion bonding of a CoCrNi-based medium-entropy alloy (MEA) to a DD5 single-crystal superalloy. The microstructure and mechanical properties of the joint diffusion-bonded at variable bonding temperatures were investigated. The formation of diffusion zone, mainly composed of the Ni [...] Read more.
This study focuses on the diffusion bonding of a CoCrNi-based medium-entropy alloy (MEA) to a DD5 single-crystal superalloy. The microstructure and mechanical properties of the joint diffusion-bonded at variable bonding temperatures were investigated. The formation of diffusion zone, mainly composed of the Ni3(Al, Ti)-type γ′ precipitates and Ni-rich MEA matrix, effectively guaranteed the reliable joining of MEA and DD5 substrates. As the bonding temperature increased, so did the width of the diffusion zone, and the interfacial microvoids significantly closed, representing the enhancement of interface bonding. Both tensile strength and elongation of the joint diffusion-bonded at 1110 °C were superior to those of the joints diffusion-bonded at low temperatures (1020, 1050, and 1080 °C), and the maximum tensile strength and elongation of 1045 MPa and 22.7% were obtained. However, elevated temperature produced an adverse effect that appeared as grain coarsening of the MEA substrate. The ductile fracture of the joint occurred in the MEA substrate (1110 °C), whereas the tensile strength was lower than that of the MEA before diffusion bonding (approximately 1.3 GPa). Full article
(This article belongs to the Special Issue The Joining of High Entropy Alloys and the Brazing Filler Metals Using High Entropy Alloys)
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12 pages, 4361 KiB  
Article
On Novel Copper Based Alloys Development via Friction Stir Alloying
by Khaja Moiduddin, Arshad Noor Siddiquee, Mustufa Haider Abidi, Syed Hammad Mian and Muneer Khan Mohammed
Crystals 2021, 11(5), 498; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11050498 - 01 May 2021
Cited by 4 | Viewed by 1690
Abstract
Friction stir alloying (FSA) of commercially pure Cu with Ni, Zn, and Mg is implemented in the current study. Mechanical and microstructural aspects of the successfully fabricated alloy structure have been examined. Energy dispersive X-ray spectroscopy revealed a uniform distribution of alloying elements [...] Read more.
Friction stir alloying (FSA) of commercially pure Cu with Ni, Zn, and Mg is implemented in the current study. Mechanical and microstructural aspects of the successfully fabricated alloy structure have been examined. Energy dispersive X-ray spectroscopy revealed a uniform distribution of alloying elements and coalescence at the atomic level. The compositional and grain size heterogeneity is managed in the stir zone, allowing for microstructural control with FSA. Thus, the present study is essential for the development of novel materials whose fabrication requires temperature well below the melting point of base metals. The alloying process is found to be accompanied by ultra-refined grains, with the smallest grain size being ~0.44 μm. The fabricated alloy managed to retain the FCC phase, and no brittle intermetallic compounds formed, according to X-ray diffraction. The fabricated alloy exhibits maximum and average microhardness enhancements of 18.4% and 6%, respectively. Tensile properties have also been investigated and correlated with microstructural morphology. A shift toward grain bimodality has also been documented, which is a highly sought-after property nowadays, especially to overcome the strength-ductility trade-off. Full article
(This article belongs to the Special Issue The Joining of High Entropy Alloys and the Brazing Filler Metals Using High Entropy Alloys)
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12 pages, 4317 KiB  
Article
Microstructure and Shear Strength of Brazing High Entropy TiZrHfNbMo Alloy and Si3N4 Ceramics Joints
by Xiaohong Wang, Duo Dong, Xiaohong Yang, Peng Huang, Kangqiao Shi, Tengfei Ma, Dongdong Zhu and Li Liu
Crystals 2021, 11(5), 472; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11050472 - 23 Apr 2021
Cited by 8 | Viewed by 2126
Abstract
The effects of different brazing processes on the interfacial microstructure and shear strength of TiZrHfNbMo high-entropy alloy (HEAS) and Si3N4 ceramic brazed joints were studied. There is no obvious defect in a brazed TiZrHfNbMo HEAS/AgCuTi/Si3N4 ceramic joint, [...] Read more.
The effects of different brazing processes on the interfacial microstructure and shear strength of TiZrHfNbMo high-entropy alloy (HEAS) and Si3N4 ceramic brazed joints were studied. There is no obvious defect in a brazed TiZrHfNbMo HEAS/AgCuTi/Si3N4 ceramic joint, and the two materials have good metallurgical bonding. The typical interface microstructure is Si3N4/Ti5Si3/Ag solid solution +Cu (s,s)+ CuTi/Cu2Ti/Cu4Ti + TiCu(Hf,Zr)NbMo/TiZrHfNbMo HEAs. With the increase of brazing temperature, the dispersed CuTi phase agglomerates in the brazed joint, and acts as the nucleate of the Cu-based solid solution. The thickness of the reaction layer increases with the increase of phases in the reaction layer on both sides of the joint. When the brazing temperature is 800 °C, 820 °C, 840 °C and 860 °C, the shear strength of the brazed joint is 30 MPa, 72 MPa, 86 MPa and 21 MPa, respectively. The formation of CuTi and Ti5Si3 intermetallic compounds increases the thickness of the reaction layer, and improves the strength of the joint. However, excessive CuTi and Ti5Si3 intermetallic compounds lead to a significant decrease in joint strength. The grain coarsening of the joint can also affect the strength of the joint. Full article
(This article belongs to the Special Issue The Joining of High Entropy Alloys and the Brazing Filler Metals Using High Entropy Alloys)
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