Corrosion of high entropy alloys

Abstract

High entropy alloys represent a unique class of metal alloys, comprising nominally five or more elements in near equiatomic proportions. High entropy alloys have gained significant interest on the basis that the high configurational entropy of such alloy systems is purported to result in a single-phase solid solution structure. While such a single-phase structure can occur in unique systems, it is now appreciated that the definition of high entropy alloys can be broader, with systems comprising only four elements possible of forming single phases, and most five (or more) element systems actually being multi (>2) phases. To this end, the notion of compositionally complex alloys is a more general description, with the concise review herein focusing on the corrosion of compositionally complex alloys (inclusive of high entropy alloys). It is noted that generally, in spite of complex compositions and in many cases complicated microstructural heterogeneity, compositionally complex alloys are nominally corrosion-resistant. This is discussed and aspects of the status and needs are presented.

Engineering heterostructured grains to enhance strength in a single-phase high-entropy alloy with maintained ductility

“…As a result, CG fcc HEAs usually exhibit excellent ductility but insufficient strength at room temperature, especially relatively low yield strength (lower than 350 MPa) [11]. While the strength of these alloys remains low, high radiation tolerance [14], excellent corrosion resistance [15] and exceptional fracture toughness [16], make single-phase fcc HEAs promising candidates for various applications. Hence, it would be desirable to develop novel design strategies to engineer the strength in these alloys.…”

High-temperature oxidation behaviour of AlxFeCrCoNi and AlTiVCr compositionally complex alloys

“…The microstructure of the AlTiVCr and Al0.9FeCrCoNi CCAs, in the as-arc melted condition, has been described in detail [26,27], and briefly summarised here. The lightweight alloy (AlTiVCr) is single-phase CCA, displaying the characteristics of a uniform B2 structure ( Fig.…”

“…As previously described in [26], the FCC phase is Co-Fe-Cr rich, BCC is Fe-Cr rich while B2 phase is Ni-Al rich. These two CCAs exhibit outstanding room-temperature properties including high hardness and superior aqueous corrosion resistance as compared with e.g., 304SS [7,26,27]. Herein, the high-temperature oxidation performance of the two CCAs was studied for the first time at 700 and 900°C.…”

“…SEM and TEM (Dark field, bright field, and high-angle annular dark field imaging as well as selected area electron diffraction) analysis revealing the microstructure of: (a) the AlTiVCr CCA, and (b) the Al0.9FeCrCoNi CCA. That the microstructure of the alloys is further described in[7,26,27].The mass change of the alloys under investigation as a function of time as well as microscopy results revealing the surface morphology and chemistry of the two CCAs after oxidation experiments at 700 and 900°C are presented inFig. 3.…”

Real-time dissolution of a compositionally complex alloy using inline ICP and correlation with XPS

“…The recent interest in high entropy alloys (HEAs) [1][2][3] has generated a large number of studies regarding alloys that are derived from the design concepts behind high entropy alloys.…”