Delineation of the reaction mechanism of Ti2AlC MAX‐phase formation during spark plasma sintering synthesis

Abstract Despite several attempts to synthesize Ti2AlC MAX‐phase using different processes and input materials, a comprehensive understanding of its formation mechanism is still lacking. This study reports, for the first time, a novel reaction mechanism of Ti2AlC MAX‐phase formation, based on extensive microstructural characterizations and density functional theory (DFT)‐based ab initio calculations. A systematic investigation was carried out up to 1400°C temperature to understand the phase transformation behavior in stoichiometric 2Ti:Al:C elemental powder mixture during spark plasma synthesis of Ti2AlC MAX‐phase. An integrated approach was adopted to establish correlations between results obtained through differential scanning calorimetry, x‐ray diffraction, scanning electron microscopy–energy‐dispersive spectroscopy–electron backscattered diffraction characterizations, and DFT calculations. Microstructural examination revealed that the formation of Ti2AlC MAX‐phase was preceded by successive transformation of Ti powder particles via a series of transient Ti–Al intermetallic formation between 660 and 1200°C, until the Ti particles get transformed into a core–shell structure of Ti2Al surrounded by TiAl intermetallic. The formation of Ti2AlC MAX‐phase was observed to occur via two different reactions. Initially, the peripheral TiAl intermetallic reacts with TiC to form Ti2AlC MAX‐phase in the temperature range of 1000–1200°C. At a later stage, the inner Ti2Al phase transforms to Ti2AlC MAX‐phase through inward carbon diffusion till 1350°C.