Tensile behaviors of Ti₃C₂T_x (MXene) films

As the most representative member of a new emerging family of 2D material, titanium carbides or nitrides (MXenes), Ti₃C₂T_x and its 2D assembly format, Ti₃C₂T_x film, have displayed outstanding performance in a broad range of practical applications. However the mechanical behaviors of Ti₃C₂T_x films are rarely reported. We report a systematic study of the tensile behavior of Ti₃C₂T_x films. Ti₃C₂T_x films with various thicknesses (2-17 µm) were prepared by the vacuum filtration method. Quasi-static tension and cyclic tension tests were performed to investigate the deformation and fracture mechanism of Ti₃C₂T_x films. It was found that: (1) the relative sliding between Ti₃C₂T_x flakes is the dominant deformation mechanism of Ti₃C₂T_x films. Cyclic loading-releasing in tension suppresses the inter-layer sliding of Ti₃C₂T_x flakes effectively and thus the tensile strength of thicker Ti₃C₂T_x film (5 µm) film improves from 57 MPa to 67 MPa. (2) The mechanical properties of Ti₃C₂T_x films are found to be thickness dependent. When the film thickness increases from 2.3 to 17 µm, the tensile strength and elastic modulus drop from 61 to 36 MPa and from 17 to 8 GPa, respectively. This is interpreted as more structural defects presented in the through-the-thickness direction as film thickness is increased. (3) Moderate ultrasonication pretreatment (30 min) reduces the Ti₃C₂T_x flake size significantly while improving the compactness of the Ti₃C₂T_x film; and the resulting Ti₃C₂T_x film shows a linear stress-strain relationship without plastic-like deformation. As a result, the tensile strength of 5 µm thick Ti₃C₂T_x film is enhanced to 85 MPa; (4) Structural defects of the Ti₃C₂T_x film have significant effects on both the brittle-like fracture behavior and the distribution of tensile strength.