Low temperature thermal expansion, high temperature electrical conductivity, and mechanical properties of Nb_4AlC_3 ceramic synthesized by spark plasma sintering

摘要

Dense bulk Nb_4AlC_3 was in-situ fabricated by spark plasma sintering (SPS) using niobium, aluminum, and carbon black powders as starting materials. Nb_4AlC_3 was formed through the reaction between Nb_2AlC and NbC, and the decomposition of Nb_2AlC. Optimized synthesis condition of starting composition, annealing temperature, and holding time were determined as 4:1.5:2.7 (molar ratio of Nb, Al, and C), 1650deg C, and 2 min, respectively. The coefficient of thermal expansion was measured as 6.7 X 10~(-6) K~(-1) from -128 to 282 deg C. The electrical conductivity was tested as 0.76 X 10~6 OMEGA~(-1) m~(-1) at 827 deg C, showing excellent high temperature conductivity. The Vickers hardness and flexural strength were measured as 3.7 GPa and 455 MPa, respectively. The micro-indentation evaluation indicated the anisotropic response of Nb_4AlC_3 grains, reflecting the anisotropic crystal structure. Additionally, the flexural strength could remain a high value of 230 MPa up to 1400deg C.