Synthesis, microstructure, and properties of high purity Mo₂TiAlC₂ ceramics fabricated by spark plasma sintering

The synthesis, microstructure, and properties of high purity dense bulk Mo₂TiAlC₂ ceramics were studied. High purity Mo₂TiAlC₂ powder was synthesized at 1873 K starting from Mo, Ti, Al, and graphite powders with a molar ratio of 2:1:1.25:2. The synthesis mechanism of Mo₂TiAlC₂ was explored by analyzing the compositions of samples sintered at different temperatures. It was found that the Mo₂TiAlC₂ phase was formed from the reaction among Mo₃Al₂C, Mo₂C, TiC, and C. Dense Mo₂TiAlC₂ bulk sample was prepared by spark plasma sintering (SPS) at 1673 K under a pressure of 40 MPa. The relative density of the dense sample was 98.3%. The mean grain size was 3.5 μm in length and 1.5 μm in width. The typical layered structure could be clearly observed. The electrical conductivity of Mo₂TiAlC₂ ceramic measured at the temperature range of 2-300 K decreased from 0.95 × 10⁶ to 0.77 × 10⁶ Ω^-1·m^-1. Thermal conductivity measured at the temperature range of 300-1273 K decreased from 8.0 to 6.4 W·(m·K)^-1. The thermal expansion coefficient (TEC) of Mo₂TiAlC₂ measured at the temperature of 350-1100 K was calculated as 9.0 × 10^-6 K^-1. Additionally, the layered structure and fine grain size benefited for excellent mechanical properties of low intrinsic Vickers hardness of 5.2 GPa, high flexural strength of 407.9 MPa, high fracture toughness of 6.5 MPa·m^1/2, and high compressive strength of 1079 MPa. Even at the indentation load of 300 N, the residual flexural strength could hold 84% of the value of undamaged one, indicating remarkable damage tolerance. Furthermore, it was confirmed that Mo₂TiAlC₂ ceramic had a good oxidation resistance below 1200 K in the air.