Abstract: Fibrous Si3N4 monolithic ceramics with a hexagonal cell were fabricated in the preferred
orientation. The densified Si3N4 fibrous monolithic showed fracture toughness of 17 MPam1/2. An
application of SiC whisker as reinforcement exhibited higher fracture toughness (24 MPam1/2).
The influences of fiber diameter and reinforcement on the fracture toughness of these fibrous
monolithic ceramics were studied in details.
Abstract: A fracture toughness model of fibrous monolithic ceramics revealed that the major
factor that contributed to the fracture toughness in ceramics was the actual energy absorbed by
crack propagation rather than the total work of fracture. The load-displacement curve and the
crack propagation path were predicted using the derived model mirror image with that of
Abstract: A novel transparent polycrystalline silicon nitride was fabricated by hot-press sintering
with MgO and AlN as additives. The mixed powder with 3 wt.% MgO and 9 wt.% AlN was sintered
at 1900oC for 1 hour under 30 MPa pressure in a nitrogen gas atmosphere. Transparent
polycrystalline silicon nitride was successfully fabricated. The mechanical properties such as
density, hardness, young’s modulus, fracture strength and fracture toughness were evaluated. The
effect of α/β phase on the mechanical properties of transparent polycrystalline silicon nitride was
investigated. The properties were changed depending on the amount of α/β phase. The hardness and
Young's modulus increased with increasing the volume fraction of α-phase fraction as a reflection
of the higher hardness of α-phase Si3N4. The fracture toughness and fracture strength decreased
with decreasing the volume fraction of β-phase Si3N4.
Abstract: The conductive composites in which nano RuO2 particles are dispersed throughout a
glass matrix have been successfully fabricated by sintering at 850°C. The sensing properties of
conductive composites were investigated in real time during tensile testing by measuring the
electrical resistance. It is shown that the excellent sensing ability based on electrical resistance
changes in the low strain range was due to deformation of conduction paths between nano RuO2
particles by brittle fracture of the glass matrix. The change of electrical resistance depends strongly
on the volume percent of Al2O3 fiber reinforcement.
Abstract: The photon emission accompanying fracture of a polycrystalline MgO was investigated at
room temperature under N2 gas pressures from 10-4 to 105 Pa. At fracture, the ultraviolet, visible and
infrared photon emissions instantaneously increased, and then rapidly decreased in most of the
experimental conditions. However, in a N2 gas pressure of around 100 Pa, their peak counts lasted for
about 10 milliseconds, and the amount of the UV photon emission was fifteen times larger than those
obtained in the other N2 gas pressures. This abrupt increment in the emission was explained by the
luminescence due to N2 gas discharge according to the classical Townsend’s theory. In conclusion,
the photon emission accompanying fracture of a polycrystalline MgO mainly originated from the
excited defects as reported by the authors previously, but the N2 gas discharge had a supplementary
effect on the emission around a specific N2 gas pressure.
Abstract: Methylsilsesquioxane films were formed on glass substrates by dropping a sol prepared
from methyltriethoxysilane and then heat-treated in an oven. Nanoindentation test was performed to
assess the elastoplastic properties of the films, including the relative residual depth ξr, Meyer hardness
HM, work-of-indentation WI and the elastic modulus E’. The values of ξr, HM and WI were obtained by
a Berkovich indenter and E’ was determined by a spherical indenter on the basis of Hertz elastic
theory. ξr decreased with the increase in the heat treatment time, whereas HM , WI and E’ significantly
increased with the time. The changes in the mechanical properties with the heat treatment time well
reflected the evolution of the Si-O-Si network structure in methylsilsequioxane film.
Abstract: Anodic aluminum oxide (AAO) was prepared in three types of aqueous solutions with
various applied voltage. The mechanical property of AAO prepared in different electrolyte was
investigated and hardness was increased on account of the increase of the thickness between pores.
The mechanical property and microstructure change of AAO prepared in oxalic acid at 40V was
investigated by heat treatment. AAO prepared in oxalic acid at 40V was transformed from amorphous
to crystalline phase by heat treatment above 800oC and hardness was increased about 2.6 times with
increase of heat treatment temperature.
Abstract: Nano-structured aluminum was fabricated by accumulative roll-bonding (ARB)
process using different rolling methods. One is the ARB using conventional rolling (CR) in
which the speed of two rolls (3.0m/min) was equal to each other. The other is the ARB using
differential speed rolling (DSR) in which the speed of two rolls is different to each other. The
roll peripheral speed of one roll was 2.0m/min and that of another roll was 3.6m/min. The roll
speed ratio was kept at 1.8. The ARB was conducted up to 6 cycles at ambient temperature
without lubrication. In both cases, the ultrafine grains were developed in the samples. The grains
formed by the DSR-ARB were more equiaxed and finer than those produced by the CR-ARB.
Tensile strength of the DSR-ARB processed sample was superior to that of the CR-ARB
processed one. The elongation was not affected significantly by the number of ARB cycles in
both cases. Texture analysis demonstrated that the shear strain, in the case of DSR-ARB, was
introduced into the center of thickness. It was concluded that the DSR-ARB process was more
effective for grain refinement and strengthening than the CR-ARB process.
Abstract: Infiltrant aluminum was infiltrated into molybdenum disilicide preforms in N2 atmosphere
at different temperatures by liquid reactive infiltration processing. The mechanical properties and
phase composition of these materials were analyzed and discussed. The experimental results showed
that the samples were corresponding to 10 at.% Al averagely after sintered, and consisted of
Mo(Al,Si)2 phase and Al-Si alloy phase. High infiltration temperature would lead to Al deficiency
mainly in Al-Si alloy phase. The highest bending strength of 737 MPa was reached at infiltration
temperature of 1350 °C because the sample had fine and integrated grains, and the strong combination
between particles. When the infiltration temperature was higher than 1350 °C, the bending strength of
material prepared would decrease because of the phase fragmentation.
Abstract: 6061 aluminum alloy composite reinforced with α-alumina and aluminum borate is
fabricated by casting method. The above mentioned composite has been compared to a similar
composite without aluminum borate reinforcement for their machinability. The aluminum borate
filler was controlled up to (2.5, 5.0 and 30vol %) on the surface of α-alumina. The reaction zone
between alumina and the matrix in both the systems are analyzed with the help of TEM micrographs
as well as X-ray diffraction profiles. At the reaction zone between alumina and the aluminum alloys,
some spinel-like compounds (MgAl2O4) are identified. Finally, machinability was analyzed with the
single point tool machining.