Sintering mechanism of CoCrFeMnNi high-entropy alloy powders

Abstract

High-entropy alloys (HEAs) have emerged as a new alloy system, with many attractive properties. Among the fabrication routes, mechanical alloying followed by sintering, have been widely used. However, sintering mechanisms of HEA powders have not yet been fully understood. This work attempts to understand the sintering kinetics of CoCrFeNiMn HEA powders. A comparative study has been done on CoCrFeNiMn alloy powders on as-milled and annealed conditions, which revealed different sintering behaviours. Decreasing densification rates with increasing activation energies were observed through dilatometry after the annealing treatment. Combined diffusion coefficients and activation energies analysed through the sintering models indicate that during sintering of the as-milled powder, mass transport occurred through several modes. On the other hand, the annealed CoCrFeNiMn alloy powder (which was nearly single phase) clearly reveals volume diffusion as the controlling mechanism during sintering. It was characterised with large activation energy.

High-entropy alloys fabricated via powder metallurgy. A critical review

“…Differential scanning calorimetry (DSC) and differential thermal analysis (DTA) have been widely used to analyse the phase transformation in the atomised or mechanically alloyed powders before the consolidation step (i.e. [143,159] among many others), but only a few works use these kinds of techniques to study the consolidated material manufactured by the conventional PM route [141,161]) or AM ( [77,258]). In [65] and [166] thermal analysis techniques are used to evaluate changes with different cooling or heating rates.…”

Tungsten Matrix Composite Reinforced with CoCrFeMnNi High-Entropy Alloy: Impact of Processing Routes on Microstructure and Mechanical Properties

“…al. [42] during the Figure 3 shows the X-ray diffraction patterns of elemental W powder, CoCrFeMnNi HEA powders and WHHEA bulk samples. W powders show the presence of a body-centered cubic (bcc) crystal structure, which confirms with the Joint Committee on Powder Diffraction Standards (JCPDS) number: 9-4900.…”

“…al. [42] during the preparation of CoCrFeMnNi HEA by mechanical alloying. Moreover, the Cr-rich σ-phase has been found very commonly in Cr-containing HEAs in mechanical alloyed condition [43] as well as in heat treated cast alloys [44].…”

Microstructure and mechanical properties of a CoCrFeMnNi high entropy alloy processed by milling and spark plasma sintering

“…Most of the time, the alloy was formed via mechanical alloying (ie: using pure metals as starting materials) and complex, multiphased and sometimes metastable microstructures were formed. For example, milling Co, Cr, Fe, Mn and Ni powders in equiatomic proportion leads to the formation of several phases (fcc, bcc, σ, amorphous) [24][25][26], although a single fcc phase is thermodynamically predicted for this composition [5]. Sometimes, new phases are formed, or some phases disappear during subsequent sintering [24,26,27].…”

“…For example, milling Co, Cr, Fe, Mn and Ni powders in equiatomic proportion leads to the formation of several phases (fcc, bcc, σ, amorphous) [24][25][26], although a single fcc phase is thermodynamically predicted for this composition [5]. Sometimes, new phases are formed, or some phases disappear during subsequent sintering [24,26,27]. Thus, the capacity of ball-milling to produce metastable phases, which is often desired, becomes a drawback for HEA for which the stable phases are the ones of interest.…”