Herein, two new two-dimensional Nb 4 C 3 -based solid solutions (MXenes), (Nb 0.8 ,Ti 0.2 ) 4 C 3 T x and (Nb 0.8 ,Zr 0.2 ) 4 C 3 T x (where T is a surface termination) were synthesized-as confirmed by Xray diffraction-from their corresponding MAX phase precursors (Nb 0.8 ,Ti 0.2 ) 4 AlC 3 and (Nb 0.8 ,Zr 0.2 ) 4 AlC 3 . This is the first report on a Zr-containing MXene. Intercalation of Li ions into these two compositions, and Nb 4 C 3 T x was studied to determine the potential of those materials for energy storage applications. Lithiation and delithiation peaks at 2.26 and 2.35 V, respectively, appeared in the case of Nb 4 C 3 T x , but were not present in Nb 2 CT x . After 20 cycles at a rate of C/4, the specific capacities of (Nb 0.8 ,Ti 0.2 ) 4 C 3 T x and (Nb 0.8 ,Zr 0.2 ) 4 C 3 T x were 158 and 132 mAh/g, respectively, both slightly lower than the capacity of Nb 4 C 3 T x .

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Fully dense (TiB2 + SiC) reinforced Ti3SiC2 composites with 15 vol% TiB2 and 0–15 vol% SiC were designed and synthesized by in situ reaction hot pressing. The increase in SiC content promoted densification and significantly inhibited the growth of Ti3SiC2 grains. The in situ incorporated TiB2 and SiC reinforcements showed columnar and equiaxed grains, respectively, providing a strengthening–toughening effect by the synergistic action of particulate reinforcement, grain's pulling out, “self‐reinforcement,” crack deflection, and grain refining. A maximum bending strength of 881 MPa and a fracture toughness of 9.24 MPam1/2 were obtained at 10 vol% SiC. The Vickers hardness of the composites increased monotonously from 9.6 to 12.5 GPa.

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