Improvement of mechanical properties and investigation of strengthening mechanisms on the Ti <sub>3</sub>AlC <sub>2</sub> ceramic with nanosized WC addition
Yijun Zhong, Ying Liu, Qinkai Jiang, Na Jin, Zifeng Lin, Jinwen Ye
Abstract
Ti<sub>3</sub>AlC<sub>2</sub> (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 Ti<sub>3</sub>AlC<sub>2</sub> and WC powders as raw materials and successfully fabricated textured (Ti,W)<sub>3</sub>AlC<sub>2</sub> ceramic with small amounts of TiC and Al<sub>2</sub>O<sub>3</sub>, and room temperature mechanical properties such as flexural strength (1146±46.9 MPa), fracture toughness (11.78±0.44 MPa·m<sup>1/2</sup>), 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)<sub>3</sub>AlC<sub>2</sub> 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 Ti<sub>1</sub> and Ti<sub>2</sub> sites of Ti<sub>3</sub>AlC<sub>2</sub>, 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)<sub>3</sub>AlC<sub>2</sub> along different crystal planes, providing superior resistance to transgranular fracture; a lower mismatch degree of (Ti,W)<sub>3</sub>AlC<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> resulted in stronger interface bonding, resulting in greater resistance to intergranular fracture as well as more balanced stress distributions at different interfaces.