Synthesis of a New High-Entropy MAX Phase (V0.2Nb0.2Ta0.2Mo0.2W0.2)2AlC and its Thermal Stability Mechanism

A new high-entropy MAX phase (V 0.2 Nb 0.2 Ta 0.2 Mo 0.2 W 0.2 ) 2 AlC was successfully synthesized at 1500 ℃ by nonpressure sintering one-step solid phase reaction method. The microstructure, crystal structure and oxidation behavior of high-entropy (V 0.2 Nb 0.2 Ta 0.2 Mo 0.2 W 0.2 ) 2 AlC MAX phase were investigated. Using thermogravimetry analysis to investigate the oxidative stability of (V 0.2 Nb 0.2 Ta 0.2 Mo 0.2 W 0.2 ) 2 AlC in air environment at high temperature from 0 to 1000 °C, there is no volume change from 0 to 400 °C, and the morphology still exhibits a typical layered structure, demonstrating thermal stability. Oxidation rate gradually decreases with the increase in temperature, and the K p3 value decreases to 0.86 × 10 –4  kg 2  m −4  s 2 at 1000 ℃. The microscopic morphology analysis at different temperatures shows that the surface defects of the matrix gradually form under high-temperature conditions, in which the formation of carbide and Al 2 O 3 layers hinds the further oxidation of the sample. The research provides a reference for the synthesis and thermal stability of new two-dimensional layered high-entropy MAX ceramics.