Tensile ductility of an AlCoCrFeNi multi-phase high-entropy alloy through hot isostatic pressing (HIP) and homogenization

Abstract

The microstructure and phase composition of an AlCoCrFeNi high-entropy alloy (HEA) were studied in as-cast (AlCoCrFeNi-AC, AC represents as-cast) and homogenized (AlCoCrFeNi-HP, HP signifies hot isostatic pressed and homogenized) conditions. The AlCoCrFeNi-AC ally has a dendritrical structure in the consisting primarily of a nano-lamellar mixture of A2 [disorder body-centered-cubic (BCC)] and B2 (ordered BCC) phases, formed by an eutectic reaction. The homogenization heat treatment, consisting of hot isostatic pressed for 1 hour at 1,100 °C, 207 MPa and annealing at 1,150 °C for 50 hours, resulted in an increase in the volume fraction of the A1 phase and formation of a Sigma () phase. Tensile properties in ascast and homogenized conditions are reported at 700 °C. The ultimate tensile strength was virtually unaffected by heat treatment, and was 396 ± 4 MPa at 700 °C. However, 2 homogenization produced a noticeable increase in ductility. The AlCoCrFeNi-AC alloy showed a tensile elongation of only 1.0 %, while after the heat-treatment, the elongation of AlCoCrFeNi-HP was 11.7 %. Thermodynamic modeling of non-equilibrium and equilibrium phase diagrams for the AlCoCrFeNi HEA gave good agreement with the experimental observations of the phase contents in the AlCoCrFeNi-AC and AlCoCrFeNi-HP. The reasons for the improvement of ductility after the heat treatment and the crack initiation subjected to tensile loading were discussed.

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

“…The density of the as-sintered AlCoCrFeNi HEA was 7.05 g/cm 3 , which was higher than the values of the same HEA that was prepared by vacuum arc-melting and then hot isostatic pressing [8]. This could be attributed to the association of liquid sintering and mechanical load during SPS which was beneficial for densifying the HEA.…”

“…High strength and ductility were mainly due to the combination of the FCC and the BCC phases. FCC phase usually had good ductility since it has more slip systems and higher symmetry than BCC phase [1,8]. The combined action of higher Al content than the FCC phase, which could cause strong solid-solution strengthening since the larger atomic size of Al [1,3], and the spinodal structure resulted in a significant strengthening effect in the BCC phases.…”

“…It can be seen that the cracks propagated mainly throughout the FCC phase or along the interfaces between the FCC and BCC phases. The cracks were difficult to propagate in the BCC phases, as it had high hardness and strength [8]. When the cracks propagated in FCC phase, the cracks could be blunted, bridged and arrested by the FCC phase since it had excellent ductility.…”

“…The AlCoCrFeNi HEA was selected for study because it has been widely studied and has a good prospect in engineering application [6][7][8][9][10]. The method is simple and offers an inexpensive and high-efficient route to prepare HEAs, which has great potential for preparing HEAs in future.…”

Influence of Annealing on the Microstructures and Oxidation Behaviors of Al8(CoCrFeNi)92, Al15(CoCrFeNi)85, and Al30(CoCrFeNi)70 High-Entropy Alloys

“…This particular alloy system is ideal for a fundamental oxidation study since it contains both Al and Cr, which are known to produce protective Cr 2 O 3 and/or Al 2 O 3 scales [30]. Additionally, the AlCoCrFeNi system is one of the most thoroughly investigated to date [1,4,10,14,[31][32][33][34][35][36][37][38][39][40][41][42][43]. This paper will systematically report the influence of annealing on the microstructures and active oxidation mechanisms.…”