In situ reaction synthesis, electrical and thermal, and mechanical properties of Nb ₄AlC ₃

In this work, a bulk Nb ₄AlC ₃ ceramic was prepared by an in situ reaction/hot pressing method using Nb, Al, and C as the starting materials. The reaction path, microstructure, physical, and mechanical properties of Nb ₄AlC ₃ were systematically investigated. The thermal expansion coefficient was determined as 7.2×10 ^-6 K ^-1 in the temperature range of 200°-1100°C. The thermal conductivity of Nb ₄AlC ₃ increased from 13.5 W. (m . K) ^-1 at room temperature to 21.2 W. (m . K) ^-1 at 1227°C, and the electrical conductivity decreased from 3.35×10 ⁶ to 1.13×10 ⁶ ω ^-1.m ^-1 in a temperature range of 5-300 K. Nb ₄AlC ₃ possessed a low hardness of 2.6 GPa, high flexural strength of 346 MPa, and high fracture toughness of 7.1 MPa.m ^1/2. Most significantly, Nb ₄AlC ₃ could retain high modulus and strength up to very high temperatures. The Young's modulus at 1580°C was 241 GPa (79% of that at room temperature), and the flexural strength could retain the ambient strength value without any degradation up to the maximum measured temperature of 1400°C.