ULTRAFINE SIC PRODUCED VIA LIQUID PHASE SINTERING,
D. Sciti, S. Guicciardi, A. Bellosi, CNR-ISTEC, Via Granarolo 64, 48018 -
Faenza, Italy

Ceramics with grain sizes down to the nanometer range have attracted a
lot of scientific interest as an increase in hardness, mechanical
strength, Weibull modulus and wear resistance is expected.
SiC ceramics are promising candidate materials for high temperature
structural components in heat engines, heat exchangers and wear
resistant components. Liquid phase sintering of SiC has been widely
investigated as complete densification can be achieved at temperatures
ranging between 1850 and 1900C.
In this work, SiC ceramics having mean grain size of about 150 nm
were produced by hot pressing at 1870C and 30 MPa starting from
different SiC nanosized powders, through liquid phase sintering, that
is formed by the addition of sintering aids (Al[2]O[3]+Y[2]O[3]). The
amount of additives ranges from 6.7 to 10 wt% and the Al[2]O[3]
/Y[2]O[3 ]ratio is varied in order to optimize the sintering behaviour
and microstructure. Grain size and morphology and grain boundary
phases were analysed by XRD, SEM, EDX, TEM. Some mechanical
properties were measured: 4-pt bending strength up to 1300C,
indentation toughness, Vickers hardness and Young modulus.

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