Abstract: SiC whisker reinforced (Mo,W)Si2 composite powder has been successfully synthesized by a
novel process, named as chemical oven self-propagating high temperature synthesis (COSHS). The
mixtures of Si and Ti powders were ignited as chemical oven. XRD result shows that the combustion
product is mainly composed of (Mo,W)Si2 solid solution and SiC phases. SEM photo and EDS result
show that SiC whisker is formed during this process. The as-prepared SiCW/(Mo,W)Si2 composite
powder has been pressureless sintered. The microstructure and mechanical properties of the composite
were investigated. Relative densities of the monolithic material and composite are 91.2% and 92.2%,
respectively. The composite containing SiC whisker and (Mo,W)Si2 solid solution has higher Vickers
hardness than monolithic MoSi2. Especially the room-temperature flexural strength of the composite is
higher than that of monolithic MoSi2, from 135.5MPa for MoSi2 to 235.6MPa for composites with
10 vol.% WSi2 and 15 vol.% SiC, increased by 73.9%. The morphology of fractured surface of composite
reveals the mechanism to improve flexural strength of MoSi2. The results of this work show that in situ
SiCW/(Mo,W)Si2 composite powder prepared by COSHS technique could be successfully sintered via
pressureless sintering process and significant improvement of room temperature flexural strength could
be achieved. It could be a cost-effective process for industry in future applications.
Abstract: Transformation of the microstructure of molybdenum disilicide heating unit in nitrogen
atmosphere at 1700°C was investigated by XRD, SEM and EDS. The results showed that MoSi2 was
transformed to polyhedral Si3N4 crystals groups distributed across in the matrix with irregular
geometry Mo5Si3 and Mo3Si crystals, and the Si3N4 crystal groups were dense areas, while the Mo5Si3
and Mo3Si groups were loose areas after being heated in nitrogen atmosphere at 1700°C for 3h. The
thickness of conversion zone of MoSi2 matrix was about 30μm and the loose Mo5Si3 and Mo3Si areas
can damage the dense structure of MoSi2 matrix.
Abstract: MoSi2 composites reinforced by carbon nanotubes were prepared by spark-discharge plasma
sintering (SPS), and the dispersion of carbon nanotubes in the MoSi2 was also discussed in this work. The
mechanical properties of MoSi2 reinforced by carbon nanotubes were measured. Investigation indicated
that the carbon nanotubes can be well dispersed by introducing the dispersant C12H25SO3Na and the
mechanical properties of the composites improved significantly. The mechanism that the composites
were reinforced and toughened were discussed in this work.
Abstract: MoSi2 was prepared by SHS, and then pressed under 300 MPa at room temperature and
sintered at 1600 °C for 1 h in a vacuum furnace. The tribological properties of MoSi2 against Al2O3 in the
temperature range from 700°C to 1100 °C were investigated. Microphotographs and phases of the worn
surface of MoSi2 were observed by SEM and XRD. Results showed that MoSi2 has well friction and wear
properties below 900 °C. When temperature rises from 900 °C to 1000 °C, wear rate of MoSi2 is raised by
20.8% which is attribute to the change of wear mechanism. The main wear mechanisms of MoSi2 are
adhesion and oxidation at high temperatures. When over 900 °C, because of ductile - brittle transition
characteristic of this material, plastic deformation and fracture are also found on the worn surface of
MoSi2. This leads to the high wear rate of MoSi2.
Abstract: Using a reticulated polyurethane sponge with interconnected pores as primal framework and
immersing into TiB2 slurry consisting of Ni and Mo as sintering additives, a porous TiB2 ceramics with
high porosity and interconnected pores was prepared by immersing and high temperature sintering
process. The rheology of TiB2 slurry which used silica sol as a binder was studied. The optimum condition
of the slurry suitable for impregnating the polyurethane sponge was obtained. The flexural strength of the
porous reticulated TiB2 ceramics can reach 1 MPa.
Abstract: In this paper, AlN powder and ceramic are prepared by microwave sintering under various
sintering environments. The microstructures of the powder and the ceramic are characterized by scanning
electron microscopy and X-ray diffraction technology. The mechanical and thermal properties of the
ceramic are studied. It was found that the sintering environment has great influence on the material
fabrication. The heat-assisted environment is beneficial to the synthesis of AlN powder. On the other
hand, the carbothermal sintering environment has the two-sided influence to the sintering of AlN ceramic.
Abstract: Effect of adding up to 5wt% CaF2 on the densification and microstructural development of hot
pressed aluminum nitride (AlN) was investigated. SEM investigation showed that the grain size of the
sintered sample decreases with the increasing content of CaF2. Secondary-phase evolution paths converge
from CA6 to CA phase above 1650°C. TEM micrographs showed that formed secondary phases could
evaporate from sintered bodies at higher temperatures in the carbon-containing nitrogen atmosphere and
the residuals were mainly distributed at triple grain junctions, keeping direct connections of AlN grains.
Translucnet AlN ceramics were prepared using CaF2 additive sintered at 1850°C for 5 h.
Abstract: Based on the nitridation reaction of aluminum with boron nitride (BN), aluminum nitride
(AlN) matrix composites were fabricated by reaction synthesis technique. The effect of the amount of Al
on the microstructure and properties was investigated. The bending strength, thermal conductivity and
dielectric constant increase with the content of aluminum. A heat-treatment schedule was performed to
investigate the effect of the microstructure on the properties. The results showed that the heat-treatment
leads to the grain growth and thermal conductivity increase with the grain growth.
Abstract: AlN/Al ceramic composite was fabricated by directed melt nitridation of pure Al block covered
with 10wt% Mg powder at 1300°C in a high purity flowing N2. Microstructure and phase composition of
the composite were investigated by scanning electron microscopy with energy dispersive spectroscopy
and X-ray diffraction. Results showed that AlN is the main phase in the composite and its lattice parameters
of a and c are 3.1110Å and 4.9806Å, respectively. The phase composition of the composite changes
along the growth direction and a gradient sandwich structure forms. The surface of the composite is made
up of a dense and thin nodular AlN layer, underneath which an AlN/Al layer appears, followed by an
AlN/Al/MgAl2O4 layer. Thermodynamic calculations predicted the formation of possible phases with the
addition of Mg. It suggested that the content of Mg at the reaction frontier of nitridation is considerably
lower to 0.15wt% where MgAl2O4 was stable, because of escape and reaction exhaustion of Mg. Once Mg
is lower than 0.05wt%, only a dense AlN layer can exist, which prevents the further nitridation of Al melt.
Abstract: Braided silica fibers reinforced nitride composite (SFRN), which was prepared by the
polymeric precursor infiltration and pyrolysis (PIP) process with the precursor polyborosilazane (PSBZ),
was a new typed microwave transparent material with high mechanical and ablation resistance
performance for high-temperature application. The thermal ablation performance of the SFRN was
evaluated by the ablation equipment with the kerosene and liquid oxygen as the heating source. The
ablation surface texture of the SFRN including macrostructure and roughness were measured by
Three-dimensional Macrostructure and Contour Scale System (TMCSS). Results showed that there are
no concurrent observation of thermal delaminations or cracks and the specimen remains intact. The SFRN
has an excellent thermal shock resistance and good ablation resistance with the linear recession rate of
0.038mm/s. The ablation surface texture of the SFRN can be well illuminated by the TMCSS. And the
ablation performance will be improved by enhancing material density and homogeneous intertextures.