Solid-state synthesis of Cr₂AlC MAX phase from mechanically activated Cr/Al/C powder blends

This study focuses on synthesizing the ternary-layered chromium aluminum carbide phase (Cr₂AlC MAX) via a milling-assisted solid-state synthesis method. The elemental powders of Cr, Al, and C were processed in a two-stage process following mechanical activation (MAc) and annealing. Various parameters in both stages (such as milling time, annealing temperature, and process control agent) were examined to optimize the production of a high-purity Cr₂AlC MAX phase. For this purpose, the elemental powders underwent MAc through high-energy ball milling for 1, 3, and 5 h and annealing at temperatures ranging from 700 to 1500 °C. The formation mechanism of the Cr₂AlC phase was discussed based on detailed characterizations, including differential thermal calorimetry (DSC), X-ray diffraction (XRD), and Rietveld analyses. Additionally, the morphological properties of the synthesized powders were investigated in detail via scanning and transmission electron microscopy (SEM and TEM) techniques. The initial formation of the MAX phase was observed at 700 °C, and it was completed with a meager amount of chromium carbide phase at higher temperatures (99.7 % Cr₂AlC at 1100 °C) depending on the synthesis conditions. In addition, a single-phase Cr₂AlC MAX without a carbide impurity was achieved with the addition of SA, which caused an increase in the annealing temperature to 1300 °C.