Characterization of MoAlB ceramics synthesized via spark plasma sintering with Si addition and SiC reinforcement

Abstract

The MoAlB phase with high purity and density from elemental precursors was successfully synthesized with SPS (Spark Plasma Sintering) at 1200 °C. Then, MoAlB-Si solid solution and MoAlB-SiC (5% SiC by volume) composite were fabricated to improve the mechanical properties and oxidation behavior of the MoAlB further. XRD (X-Ray Diffraction), SEM (Scanning Electron Microscopy), and EDS (Energy Dispersive X-Ray Spectroscopy) investigated the composition and microstructure of the MoAlB ceramics. The hardness was measured by the Vickers indentation test, and fracture toughness was calculated by radial cracks formed during the indentation test. The hardness and fracture toughness of pure MoAlB was 10.30 GPa and 6.73 MPa.m1/2. With the Si solid solution, the hardness increased to 11.93 GPa, while the fracture toughness decreased to 5.49 MPa.m1/2. The highest hardness and fracture toughness were obtained in the MoAlB-SiC composite, 12.39 GPa, and 7.38 MPa.m1/2, respectively. The oxidation tests of the samples were characterized in the air at 1200 ℃ for 12 h. A dense and continuous oxide layer was formed in all samples after 12 h at 1200 °C. While both Si solid solution and SiC reinforcement increase the oxidation resistance, the best results were obtained in the MoAlB-Si-SiC composite. The effect of Si addition and SiC reinforcement on electrical and thermal conductivity was measured from room temperature to 1000 ⁰C. The electrical conductivity of all samples decreased exponentially with the increase in temperature. The electrical conductivity of pure MoAlB was 2.82 S⋅m−1 at room temperature and decreased with the Si addition (2.49 S⋅m−1) or SiC reinforcement (2.67 S⋅m−1). On the other hand, thermal conductivity tends to decrease between room temperature to 400 °C but showed an increasing trend above 400 °C. In conclusion, the mechanical properties and oxidation resistance of MoAlB ceramics were improved with Si addition and SiC reinforcement.