Preparation, Microstructure, and Mechanical Properties of Nb_4AlC_3-Nb_5(Si, Al)_3 Composites

摘要

Niobium aluminum carbide (Nb_4AlC_3), as a member of the MAX phases, can retain its stiffness and strength up to over 1400℃, however, the strength at room temperature is relatively low. In this work, Nb_5(Si, Al)_3 was used to strengthen Nb_4AlC_3. Nb_4AlC_3-Nb_5(Si, Al)_3 composites with different amount of Nb_5(Si, Al)_3 were synthesized from the elemental powders by in situ hot-pressing/solid-liquid reaction synthesis process. The RT flexural strength was significantly improved from 370 MPa of monolithic VN_4AlC_3 to 432 MPa of ND_4AlC_3-15 vol% Nb_5(Si, Al)_3 composite without the degradation of its high-temperature mechanical properties. While a slightly decrease in fracture toughness occurs with the increment of Nb_5(Si, Al)_3 content. Meanwhile, Transmission electron microscopy (TEM) observations reveal that the interfaces between Nb_4AlC_3/Nb_4AlC_3, Nb_4AlC_3/Nb_5(Si, Al)_3, and Nb_5(Si, Al)_3/Nb_5(Si, Al)_3 are free of amorphous layers, which is also beneficial to its high-temperature mechanical properties.