Ultra-high-temperature application of MXene: Stabilization of 2D Ti ₃C ₂T _<i>x</i> for cross-scale strengthening and toughening of 3D TiC

Abstract

The transition metal carbide/nitride core within MXenes makes them considerably useful for ultra-high temperature reinforcement. However, extensive research on Ti₃C₂T<em>_x</em> MXene has revealed its tendency to undergo a phase transition to TiC<em>_y</em> at temperatures above 800 °C due to the high activity of a superficial Ti atomic layer. Herein, spark plasma sintering of Ti₃C₂T<em>_x</em> and TiC is performed to prevent the Ti₃C₂T<em>_x</em> phase transition at temperatures up to 1900 °C through the fabrication of composites under a pressure of 50 MPa. Using a focused ion beam scanning electron microscope to separate the layered substances in the composites and examining selected area diffraction spots in a transmission electron microscope enabled identification of a non-phase-transitioned MXene. First-principles calculations based on density functional theory indicated the formation of strong chemical bonding interfaces between Ti₃C₂T<em>_x</em> and TiC, which imposed a stability constraint on the Ti atomic layer at the Ti₃C₂T<em>_x</em> surface. Mechanical performance tests, such as three-point bending and fracture toughness analysis, demonstrated that the addition of Ti₃C₂T<em>_x</em> can effectively improve the cross-scale strengthening and toughening of the TiC matrix, providing a new path for designing and developing two-dimensional (2D) carbides cross-scale-enhanced three-dimensional (3D) carbides with the same elements relying on a wide variety of MXenes.