Welding of High Entropy Alloys—A Review

Abstract

High-entropy alloy (HEA) offers great flexibility in materials design with 3–5 principal elements and a range of unique advantages such as good microstructure stability, mechanical strength over a broad range of temperatures and corrosion resistance, etc. Welding of high entropy alloy, as a key joining method, is an important emerging area with significant potential impact to future application-oriented research and technological developments in HEAs. The selection of feasible welding processes with optimized parameters is essential to enhance the applications of HEAs. However, the structure of the welded joints varies with material systems, welding methods and parameters. A systemic understanding of the structures and properties of the weldment is directly relevant to the application of HEAs as well as managing the effect of welding on situations such as corrosion that are known to be a service life limiting factor of welded structures in conditions such as marine environments. In this paper, key recent work on welding of HEAs is reviewed in detail focusing on the research of main HEA systems when applying different welding techniques. The experimental details including sample preparation, sample size (thickness) and welding conditions reflecting energy input are summarized and key issues are highlighted. The microstructures and properties of different welding zones, in particular the fusion zone (FZ) and the heat affected zones (HAZ), formed with different welding methods are compared and presented in details and the structure-property relationships are discussed. The work shows that the weldability of HEAs varies with the HEA composition groups and the welding method employed. Arc and laser welding of AlCoCrFeNi HEAs results in lower hardness in the FZ and HAZ and reduced overall strength. Friction stir welding results in higher hardness in the FZ and achieves comparable/higher strength of the welded joints in tensile tests. The welded HEAs are capable of maintaining a reasonable proportion of the ductility. The key structure changes including element distribution, the volume fraction of face centered cubic (FCC) and body centered cubic (BCC) phase as well as reported changes in the lattice constants are summarized and analyzed. Detailed mechanisms governing the mechanical properties including the grain size-property/hardness relationship in the form of Hall–Petch (H–P) effect for both bulk and welded structure of HEAs are compared. Finally, future challenges and main areas to research are highlighted.

A Short Review on Welding and Joining of High Entropy Alloys

“…Regarding the overall developments of welding of HEAs, a survey on the contemporary literature shows that an effort is being made towards the understanding of the microstructural evolution and optimization of these joining processes [51]. Until now, the number of publications regarding welding of HEAs is increasing throughout the years, as the developments on these alloys become more evident, as it can be observed in Figure 1.…”

New Advances in High-Entropy Alloys

“…The selection of feasible welding processes with optimized parameters is essential to enhance the applications of HEAs. Guo et al [ 13 ] reviewed the key recent works on welding of HEAs in detail, focusing on the research of main HEA systems when applying different welding techniques. They also highlighted the future challenges and main areas to research.…”

Dissimilar Infrared Brazing of CoCrFe(Mn)Ni Equiatomic High Entropy Alloys and 316 Stainless Steel

“…The joining of HEAs is crucial in the application of such new alloys for industrial applications. There are many studies on welding HEAs [35][36][37]. Good mechanical properties have been achieved in previous studies [38][39][40].…”