Abstract
High-entropy alloys (HEAs) and compositionally complex alloys (CCAs) represent new classes of materials containing five or more alloying elements (concentration of each element ranging from 5 to 35 at. %). In the present study, HEAs are defined as single-phase solid solutions; CCAs contain at least two phases. The alloy concept of HEAs/CCAs is fundamentally different from most conventional alloys and promises interesting properties for industrial applications (e.g., to overcome the strength-ductility trade-off). To date, little attention has been paid to the weldability of HEAs/CCAs encompassing effects on the welding metallurgy. It remains open whether welding of HEAs/CCAs may lead to the formation of brittle intermetallics and promote elemental segregation at crystalline defects. The effect on the weld joint properties (strength, corrosion resistance) must be investigated. The weld metal and heat-affected zone in conventional alloys are characterized by non-equilibrium microstructural evolutions that most probably occur in HEAs/CCAs. The corresponding weldability has not yet been studied in detail in the literature, and the existing information is not documented in a comprehensive way. Therefore, this study summarizes the most important results on the welding of HEAs/CCAs and their weld joint properties, classified by HEA/CCA type (focused on CoCrFeMnNi and AlxCoCrCuyFeNi system) and welding process.
Highlights
1.1 A new class of materialsRecommended for publication by Commission II - Arc Welding and Filler MetalsHigh-entropy alloys (HEAs) represent a new class of materials [1,2,3]
The sluggish diffusion effect [21, 22] assumes that high-temperature diffusion and diffusion-controlled phenomena such as oxidation [13], creep [20], phase transformations [23], and growth of particles [24] are slower in HEAs compared to conventional alloys since vacancies may be surrounded by various atomic configurations
There are further studies on welding of HEAs/compositionally complex alloy (CCA) by special processes such as explosion welding [35], diffusion welding [36], and individual examinations on refractory HEAs [37]. These investigations will not be discussed in the following, as this overview focuses on basic welding properties of the equiatomic CoCrFeMnNi HEA (“Cantor” alloy in accordance with [6]) and various compositions of the AlxCoCrCuyFeNi HEAs/ CCAs [38,39,40]
Summary
High-entropy alloys (HEAs) represent a new class of materials [1,2,3]. They usually contain more than five alloying elements and are defined in this overview as single-phase solid solutions. Cu is alloyed to the base element Al, or Al is added to Ti-base lightweight materials to improve strength Each of these alloys offers typical properties such as high mechanical strength and ductility, accompanied by a high specific weight for steels [4] that are of prime importance. Several HEAs allow overcoming the strengthductility trade-off due to their multiple principal element composition These include superior mechanical properties like specific strength [1, 2, 9,10,11], mechanical performance at high temperature [12,13,14], (shown in Fig. 2), or superior fracture toughness at cryogenic temperature [15, 16]. Other alloy concepts provide special properties like superparamagnetism [17]
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