Aluminium magnesium boride: synthesis, sintering and microstructure

AlMgB14 ceramics were reported as high-hardness materials over a decade ago. While different synthesis routes for processing of AlMgB14 ceramics were reported in the past, however the synthesis routes are still not optimised and present a significant challenge to the manufacturers. In this work six different synthesis routes were explored for the synthesis of AlMgB14 powder. The synthesised compositions were characterised by XRD, where weight fractions of each phase were calculated by Rietveld refinement. The bulk ceramics were sintered using powder with the highest yield (93.2%) of AlMgB14 phase by spark plasma sintering at 1315 degrees C and 50MPa. Both phase composition and microstructure of the sintered AlMgB14 were characterised by XRD and SEM/EDS, which revealed the existence of AlMgB14, MgAl2O4 and a small amount of unreacted Al. Hardness and indentation fracture resistance of AlMgB14 ceramics were measured to be 26.7 +/- 2.2 GPa and 5.59 +/- 0.42 MPa m(1/2), respectively by Vickers indentation technique.