Sintering of covalent crystals is an important technological process
for obtaining advanced high-strength ceramic. The process complexity
is caused by the extremely high sintering temperature for these
materials and their low plasticity compared to metallic alloys.
It has been established that sintering of crystal materials is
controlled by diffusion and also plastic deformation processes. This
allows to make the assumption that the sintering temperature can be
reduced by deformation. The purpose of this report is to investigate
sintering of covalent crystals and interpret the contribution of
plastic deformation.
Germanium was chosen as a model material for investigation. The
samples for sintering were prepared from a germanium single crystal by
oriented cutting and mechanical diamond treatment of the cut surface.
Single crystals with identical orientations were sintered in the (111)
plane with correspoding [110].
Having in mind the complexity of the solid state sintering process of
covalent crystals, this process was investigated in different
thermobaric conditions-uniaxial compression and quasihydrostatic high
pressyure. Sintering of oriented crystals was carried out during
uniaxial loading with P=15MPa and temperatures up to 900 C as well as
under conditions of quasihydrostatic pressure with P=0.7GPa and
temperatures 450-710 C.
It has been shown:
1. Sintering of germanium single crystals during uniaxial loading at
temperatures close to the melting temperatures (about 900 C) is
possible.
2. In condition of high quasihydrostatic pressures, when stress is
close to the yield limit, the sintering temperature of monocrystals
significantly decreases and is about 500 C a with pressure of 0.7GPa.
3. Applied pressure reduce the characteristic deformation temperature
T* of covalent crystals, which leads to the extension of the warm
deformation interval to lower temperatures, where sintering is
followed by strengthening of the contact zone.
4. The result obtained in this work give an experimental confirmation
of the significant role of plastic deformation in the sintering of
covalent crystals.