<i>In Situ</i> Reaction Synthesis, Electrical and Thermal, and Mechanical Properties of Nb ₄ AlC ₃

Abstract

In this work, a bulk Nb 4 AlC 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 4 AlC 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 4 AlC 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 4 AlC 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 4 AlC 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.