Influence of process control agent and Al concentration on synthesis and phase stability of a mechanically alloyed AlxCoCrFeMnNi high-entropy alloy

Highlights: • The vapor pressure, polar or non-polar nature, and type of milling affect the PSD. • The O and C are incorporated as interstitial elements into the crystalline lattice. • In wet milling, the formation of the BCC structure is related to Al content. • In dry milling, the formation of the BCC structure is related to collision energy. • FCC-BCC region is broader in the Al_1.5 system than those values calculated by VEC. -- Abstract: This paper reports the effects of different process control agents (PCA) (methanol, n-heptane, and stearic acid) and aluminum concentration (x = 0.5, 1.0, and 1.5 at%) on the particle size distribution, structure, microstructure, stability, and prediction of phases in AlxCoCrFeMnNi high-entropy powder synthesized by mechanical alloying. The results showed that the vapor pressure, the polar nature of the different process control agents used, and type of milling (dry/wet) generating changes in the particle size distribution, microstructure, and crystalline structure since the use of PCA modifies the balance between the cold-welding and fracture processes. Quantitative analysis showed that the PCA chemical decomposition generated residual oxygen and carbon in all systems. X-ray diffraction showed that all systems present a mixture of crystal structures BCC-FCC with nanometric crystallite size, and the peak intensities changed in function of lattice deformation generated by type milling employed. On the other hand, the results also showed that the boundary between BCC-FCC and FCC regions is even broader and extends to higher Al concentration than those reported by the valence electron concentration criterion.