Preparation of mullite/NbN composites through spark plasma sintering

Abstract

The main objective of this article is to obtain reaction sintered mullite based ceramics through spark plasma sintering process. 5, 10 and 15 wt% NbN particles were mixed with kaolinite and alumina powders as mullite precursor through a wet milling process. The mullite ceramic and composites were fabricated by spark plasma sintering (SPS) method at 1350 °C with initial and final applied pressure of 10 and 50 MPa, respectively. All of prepared composites showed relative density higher than 99% of theoretical density as well as mullite ceramic. The XRD patterns obtained from sintered composites demonstrated dominant crystalline phase of mullite and NbN and also some low-intensity of alumina peaks were observed. The FESEM images of sintered composites illustrated uniform distribution of reinforcement particles for 5 and 10 wt% addition of NbN. While using 15 wt% NbN reinforcement phase lead to form some agglomerates areas. The optimum mechanical properties were obtained for composites containing 10 wt% NbN as bending strength of 441 ± 36 MPa, Vickers hardness of 17.89 ± 0.61 GPa and fracture toughness of 3.79 ± 0.12 MPa m1/2.