The BCC/B2 Morphologies in AlxNiCoFeCr High-Entropy Alloys

Abstract

Abstract:The present work primarily investigates the morphological evolution of the body-centered-cubic (BCC)/B2 phases in Al x NiCoFeCr high-entropy alloys (HEAs) with increasing Al content. It is found that the BCC/B2 coherent morphology is closely related to the lattice misfit between these two phases, which is sensitive to Al. There are two types of microscopic BCC/B2 morphologies in this HEA series: one is the weave-like morphology induced by the spinodal decomposition, and the other is the microstructure of a spherical disordered BCC precipitation on the ordered B2 matrix that appears in HEAs with a much higher Al content. The mechanical properties, including the compressive yielding strength and microhardness of the Al x NiCoFeCr HEAs, are also discussed in light of the concept of the valence electron concentration (VEC).

Evaluation of microstructure and mechanical property variations in AlxCoCrFeNi high entropy alloys produced by a high-throughput laser deposition method

“…Figure 3e shows the interior of the dendrites at x = 1.16 in greater detail, revealing spherical particles embedded in the matrix. Figure 3f, obtained from the interdendritic region for the same composition, shows a weave-like structure typical of spinodal decomposition, consistent with prior observations [14]. Figure 4e and 4f shows the EBSD results for x = 0.69.…”

“…Intermediate VEC values would include a mixture of the two phases. These three parameters are calculated for the compositions in the present work (using the definitions and elemental values found in Guo et al [20]) and compared with those for the compositions examined in the prior studies in Figure 8 [11,13,14]. While the two phase regime sits within Guo et al's predicted range, all 4 sets of data exhibit narrower FCC+BCC/B2 ranges than predicted.…”

“…Only the BCC/B2 structure was observed for 0.9 ≤ x ≤ 2.0. Ma et al [14] examined 6 compositions, x = 0.41 -1.33, and observed a "minor" amount of BCC phase in an FCC matrix at x = 0.41, the appearance of B2 at x = 0.57, and a BCC/B2 matrix with "minor" amounts of FCC at x = 0.74. Only the BCC/B2 structure was observed for x ≥ 0.92.…”

“…Prior studies have also measured the variation in the hardness and compressive deformation behavior of cast AlxCoCrFeNi with Al content [12][13][14]16]. The BCC/B2 structure is generally found to have higher hardness and strength than the FCC phase, due to the reduced number of dislocation slip systems in the BCC/B2 structure.…”

High-Entropy Alloys (HEAs)

“…They found that the homogenized alloy has a better hot workability than as-cast alloy, and the flow stress in a homogenized state was always higher than that in an as-cast state under the same deformation conditions. Ma et al [9] studied the morphological evolution of the body-centered-cubic (BCC)/B2 phases in Al x CoCrFeNi (x = 0.41, 0.57, 0.74, 0.92, 1.12, and 1.33) HEAs. They found that the BCC/B2 coherent morphology is closely related to the lattice misfit between these two phases: A weave-like morphology induced by the spinodal decomposition forms at lower Al contents, and spherical disordered BCC precipitates form within the ordered B2 matrix at much higher Al contents.…”