Effects of planetary ball milling on AlCoCrFeNi high entropy alloys prepared by Spark Plasma Sintering: Experiments and molecular dynamics study

Abstract

The elaboration of High Entropy Alloys (HEA) was investigated by means of powder metallurgy. We studied the combination of mechanical activation and reactive sintering in the case of AlCoCrFeNi. Elemental metallic powders were first processed by planetary ball milling over a long duration (28 h). The ratio K between the rotating speed of the sun wheel and the relative rotating speed of the grinding vials was set at 0.2 and 1 corresponding to "medium" energy milling. Given the particular hardness of chromium as compared to other elements, the effect of Cr powder size was investigated and optimized. In addition to experimental characterizations of milled powders, Molecular Dynamics simulations were carried out in order to assess the formation of solid solutions. The activated powders were then consolidated by Spark Plasma Sintering at 1000 °C and 1100 °C. A nanostructured lamellar microstructure exhibiting the coexistence of the FCC and BCC phases was synthesized by this solid-state route. The sintered materials exhibited hardness of up to 670 HV. Our final results (i.e., after optimization of the milling and sintering parameters) suggest that mechanical activation combined with reactive sintering is an efficient route to elaborate dense HEA materials.

Microstructure and composition dependence of mechanical characteristics of nanoimprinted AlCoCrFeNi high-entropy alloys

“…Therefore, the EAM potential developed by Farkas et al 66 is adopted for describing the interatomic interaction between Al–Cr–Co–Fe–Ni in the present study, which is consistent with the interaction of atoms in alloys that have been demonstrated in many previous studies 41 , 48 , 67 . The interaction force between the sample and the punch is assisted by Lennard–Jones (LJ) potential 32 , 64 .…”

“…The model size of 200 Å × 55 Å × 110 Å (L × W × H) containing between 113,088 and 114,601 atoms is generated to study the deformation behavior of FCC Al x CoCrFeNi HEAs with various crystal structures during the nanoimprinting process. The lattice constant of the FCC phase is 3.525 Å, which obtains from previous studies 41 , 42 . The punch in the diamond lattice structure consists of about 57,888 atoms, and it is loaded along the Z direction.…”

Effects of mechanical activation on chemical homogeneity and contamination level in dual-phase AlCoCrFeNi high entropy alloy

“…The peculiar state of the milled powders is the specificity of the mechanical activation process. Comprehensive characterization of the powder is reported elsewhere [28].…”

“…It is interesting to note that the TCNI9 database predicts a greater amount FCC than the TCHEA3 database (see [28] for instance). The main difference between the two databases is that the TCHEA3 database was mainly developed for equimolar and near equimolar solid solutions.…”

“…In our previous work, we studied the influence of planetary ball milling on the synthesis of AlCoCrFeNi [28]. We demonstrated that long mechanical alloying was not mandatory in the elaboration of sintered alloys with high entropy solid solutions.…”