Improvement of mechanical properties and investigation of strengthening mechanisms on the Ti3AlC2 ceramic with nanosized WC addition

Ti3AlC2 (TAC) has great potential for use as an ablation material in aerospace applications due to its great oxidation/ablation resistance, but its high-temperature strength and thermal shock resistance still have much room for simultaneous improvement under fast temperature variation conditions. Herein, we used Ti3AlC2 and WC powders as raw materials and successfully fabricated textured (Ti,W)3AlC2 ceramic with small amounts of TiC and Al2O3, and room temperature mechanical properties such as flexural strength (1146 +/- 46.9 MPa), fracture toughness (11.78 +/- 0.44 MPa<middle dot>m1/2), and hardness (5.81 +/- 0.11 GPa) at 5 wt% WC addition were achieved. The high-temperature strength of the ceramic was significantly improved, and better thermal shock resistance from 298 to 1173 K was simultaneously acquired together with the regulation of the elastic modulus, thermal conductivity, and thermal expansion coefficient, providing (Ti,W)3AlC2 with more possibilities for fast-temperature variation applications. Strengthening and toughening mechanisms were proposed. Scanning transmission electron microscopy high-angle annular dark-field imaging (STEM-HADDF) showed that W randomly replaced the Ti1 and Ti2 sites of Ti3AlC2, providing a good reference for establishing crystal models, and further density functional theory (DFT) calculations based on these models indicated a higher fracture energy of (Ti,W)3AlC2 along different crystal planes, providing superior resistance to transgranular fracture; a lower mismatch degree of (Ti,W)3AlC2/Al2O3 resulted in stronger interface bonding, resulting in greater resistance to intergranular fracture as well as more balanced stress distributions at different interfaces.