DESIGN, ASSEMBLY AND CHARACTERIZATION OF COMPOSITE ...

the ZnO-B2O3-Li2O eutectic system and leads to increased sintering rate of LFBT to
match that of Ni'(m). Although this is not obvious from the observations of Figure 6.5,
the liquid phase between particles in the LFBT may allow for stress relaxation during the
isothermal holds. At the sintering temperature, the BT particle network demonstrates
plasticity, 38 and stresses are alleviated by plastic deformation of the particle network.
A direct proof of this point is the LFBT lattice fired at 800 °C, as shown in Figure
6.5. This LFBT lattice has rounded edges at a macroscopic level; and at a microscopic
level, relative positions between relevant particles must have shifted or rearranged. The
likely cause of this deformation is the temperature gradient within the particle network.
As melting absorbs heat, the outer portion must have liquid formation prior to melting of
sintering aids located at inner portion of the lattice. It also suggests that melting of
sintering aids starts around this temperature. Nevertheless, after fired at higher
temperatures, i.e. 900 °C, and 1000 °C, the rounded edge disappears and the lattice
returns to square shape. This indicates that even plastic deformation occurs during liquid
phase sintering process, the initially defined geometric characteristics may be restored
after sintering process completes. These lattices are pressureless sintered in a tube
furnace at atmospheric pressure, so the restoring effect is by the sintering process itself.
This validates the use of liquid phase sintering for near net shaping through Robocasting,
provided that the volume of liquid phase formed during sintering is much less than solid
phase so as not to generate free liquid volume and cause unwanted viscous flow of the
particles. In this work, the volume of ZnO-B2O3-Li2O sintering aids is estimated to be ~5%
of total ceramic volume in sintered LFBT.
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