A. Bondanini et al., Influence of powder characteristics and powder processing routes on microstructure and properties of hot pressed silicon nitride materials, J MATER SCI, 36(20), 2001, pp. 4851-4862
Four different commercial Si3N4 powders were hot pressed with the addition
of La2O3 and Y2O3 as sintering aids. Two powder processing routes were set
up: addition of sintering aid powders by ultrasonic dispersion, addition of
nanodispersed amorphous additive species by chemical coprecipitation. The
following aspects were analyzed: characteristics of starting powders and po
wder mixtures, with reference to surface modification (electrokinetic behav
iour and surface properties) induced by the powder treatment; sintering beh
aviour of the powder mixtures; influence of raw powders characteristics and
processing route on microstructure and properties of dense materials. The
microstructural characteristics of hot pressed materials (grain size, aspec
t ratio, grain boundary phases) were found to be dependent on powder charac
teristics and its process history. Significant variation of the mechanical
properties (Young modulus, hardness, toughness and strength) were related t
o microstructural features. Strength, for example, ranges from 600 to 1200
MPa at room temperature and from 400 to 1000 Wa at 1200 degreesC; toughness
ranges from about 4 to about 6 MPam(1/2). (C) 2001 Kluwer Academic Publish
ers.