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Abstract

The metastable high pressure ReB 2-type hexagonal OsB 2 bulk ceramics was produced by spark plasma sintering. The phase composition, microstructure, and mechanical behavior of the sintered OsB 2 were studied by X-ray diffraction, optical microscopy, TEM, SEM, EDS, and nanoindentation. The produced ceramics was rather porous and contained a mixture of hexagonal (~80 wt%) and orthorhombic (~20 wt%) phases as identified by X-ray diffraction and EBSD analysis. Two boron-rich phases, which do not contain Os, were also identified by TEM and SEM/EDS analysis.

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AlMgB 14 ceramics were reported as high-hardness materials over a decade ago. While different synthesis routes for processing of AlMgB 14 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 AlMgB 14 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 AlMgB 14 phase by spark plasma sintering at 1315°C and 50 MPa. Both phase composition and microstructure of the sintered AlMgB 14 were characterised by XRD and SEM/EDS, which revealed the existence of AlMgB 14 , MgAl 2 O 4 and a small amount of unreacted Al. Hardness and indentation fracture resistance of AlMgB 14 ceramics were measured to be 26.7 ± 2.2 GPa and 5.59 ± 0.42 MPa m 1/2 , respectively by Vickers indentation technique.