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.
The effects of carbon sources and carbon content on the
density, microstructure, hardness and elastic properties of dense SiC
ceramics were investigated. The precursor powders were prepared by adding
1.5-4.5wt.% C (carbon lamp black or phenolic resin) and 0.5 wt.% B4C to SiC
and sintered at 1900?C for 15min under 50MPa pressure in argon with an
intermediate dwell at 1400?C for 30min. The results showed that carbon lamp
black provided better mixing than phenolic resin since carbon cluster was
found in the samples made with phenolic resin. Increasing carbon content
causes the decrease of 4H polytype amount in the samples. The presence of
higher than 1.5wt.% carbon inhibits grain growth and the presence of the 4H
polytype. SiC samples can be produced with relative density of more than
99%TD with 1.5wt.% carbon lamp black addition which shows small average
grain size, high elastic modulus and hardness of 2.28 ?m, 453GPa and
21.2GPa, respectively.
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