The phase decomposition can enhance the mechanical properties of carbide ceramics effectively, which can overcome the difficulty of enhancement of mechanical properties for single-phase multi-component carbide ceramics. In this work, a series of non-stoichiometric (TiZrVNb)C_x ceramics were prepared by spark plasma sintering (SPS) at different temperatures. The effects of carbon content on phase compositions, microstructure evolution, and mechanical properties were investigated in detail. The phase decomposition took place with the reduction of carbon content. Two different solid solutions of (Ti, V)-rich and Zr-rich phases formed originating from the decomposition of equimolar single-phase solid solution, namely the Zr-poor phase and Zr-rich phase, respectively. The distribution of Nb element is relatively uniform. The semi-coherent interfaces between the Zr-poor phase and the Zr-rich phase can harden and strengthen effectively under the synergistic effect of grain refinement. The ceramics with phase decomposition structures have apparent advantages compared to single-phase high-entropy carbides. This work provides an important train of thought for the microstructure tailoring and properties optimization of multi-component carbide ceramics.

In order to solve the problem that the mechanical properties of single-phase multi-component carbide ceramics are relatively mediocre, the phase transition from single phase to multiple phases was put forward to achieve superior mechanical properties. A series of (TiZrV_xNb)C_0.8 ceramics with different V content were fabricated by spark plasma sintering (SPS). The influence of the V content on the phase compositions, microstructural evolution, and mechanical properties was investigated in detail. The transition behavior from single phase to multiple phases is discovered and discussed. The formation of the Zr-rich phase and Zr-poor phase can be attributed to the increase of lattice distortion and mixed enthalpy by adding V element. The obtained nanometer lamellar structure with semi-coherent interface via in-situ decomposing is reported for the first time in multi-component carbide ceramics. The semi-coherent interfaces with the high dislocation density and strain concentration have an effective influence on the improvement of mechanical properties as well as grain refinement and multi-phase formation. The optimal comprehensive mechanical properties of Vickers’ hardness (26.3 GPa), flexural strength (369 MPa), and fracture toughness (3.1 MPa·m^1/2) are achieved in the sample with 20 mol.% V.