Rapid preparation of AlCoCrFeNi high entropy alloy by spark plasma sintering from elemental powder mixture

High-pressure high-temperature tailoring of High Entropy Alloys for extreme environments

“…At ambient pressure, DSC results for bcc-Al 2 CoCrFeNi display a sigmoid-like reversible transition at 890 K ( Figure S1), associated by Gao in a theoretical work with the transition bcc 1 +bcc 2 +B2  bcc+B2 [44]. The divergence between the results reported here and Gao"s interpretation might arise from the profound differences in the crystal structure of the nominally equivalent starting material [36][37][38][39]. The decomposition of 40 wt.% of the B2 phase above 890 K and the exsolution of a fcc phase (a fcc1 = 3.636(8) Å) has been observed above 890 K. A second fcc 2 phase of lattice parameter a fcc2 = 3.630(6) Å develops from the first fcc phase at 1023 K (65 wt.% bcc, 25 wt.% fcc 1 , 10 wt.% fcc 2 ).…”

“…Room temperature compressibility curves for fcc-Al 0.3 CoCrFeNi and bcc-Al 2 CoCrFeNi were fitted using the third-order Birch-Murnaghan isothermal equation of state (B-M EoS) [35], which fits experimental data better in comparison with other EoS (Figure 1). The volumetric thermal expansion coefficient for bcc-Al 2 CoCrFeNi, ( ) , was obtained by fitting thermal dependence of its atomic volume: In as-cast bcc-Al 2 CoCrFeNi sample, the presence of (1 0 0) super-lattice peak in the PXRD profile of the alloy (Figures 2 and 3) indicates long-range ordering (B2 type) reported for Al-rich HEAs sub-lattice [36][37][38][39]. The lattice parameter of the as-cast alloy (a = 2.877(2) Å) is consistent with the values reported by Kao [19].…”

Creep, fatigue, and fracture behavior of high-entropy alloys

“…A much higher toughness of K q % 25.2 MPa m 1/2 for a SPS AlCoCrFeNi HEA is achieved in three-point-bending tests of the SENB specimens. 66 A combination of the cleavage fracture in the bcc phase and microvoid coalescence in the fcc phase appears on the fracture surface [ Fig. 9(d)].…”

“…64 (c) Fracture surface of the AlCoCrFeNi HEA sintered by the powder metallurgy at 1273 K. 65 (d) Secondary electron image of the fracture surface of the AlCoCrFeNi HEA. 66 initiated at the triple junction of the bcc grains, and the fcc precipitates at the bcc grain boundaries block crack propagation. Thereby, the cracks are branched into new cracks, redirected, or even terminated at grain boundaries.…”

“…13,59 The HEAs with a mixed fcc and bcc structure have a fracture toughness of 25-45 MPa m 1/2 , exhibiting a fracture morphology of brittle features in the bcc area and isolated ductile islands in the fcc area. 36,66 The CoCrFeMnNi HEA is fractured with ductile dimples nucleated at the oxides upon uniaxial-tension tests at RT, and apparent necking is noticed for the samples tested at 77 K. 13,67,68 Tension fracture in HEAs with a mixed fcc and bcc phase initiates at the interface between the two phases, and/or the precipitates at the grain boundaries. [79][80][81] HEAs with a bcc phase are compression-fractured by quasicleavage, 24,85 or intergranular fracture.…”