Abstract: Dynamic deformation and fracture behavior of Zr-based bulk metallic glass (BMG) and
BMG composite containing dendritic β phases was investigated in this study. Dynamic compressive
test results indicated that both maximum compressive stress and total strain of the BMG and BMG
composite decreased with increasing test temperature because shear bands could propagate rapidly
as the adiabatic heating effect was added at high temperatures. Above the glass transition
temperature, total strain decreased more abruptly due to crystallization of amorphous phases.
Maximum compressive stress and total strain of the BMG composite were higher than those of the
BMG because β phases played a role in forming multiple shear bands. The BMG composite having
more excellent dynamic properties than the BMG can be more reliably applied to the structures or
parts requiring dynamic properties.
Abstract: The present study aims at investigating the effects of microstructure on fracture
toughness of two A356 Al alloys. These A356 alloys were fabricated by casting processes such as
rheo-casting and casting-forging, and their mechanical properties and fracture toughness were
analyzed in relation with microfracture mechanisms. All the cast A356 alloys contained eutectic Si
particles mainly segregated along solidification cells, and the distribution of Si particles was
modified by the casting-forging process. Microfracture observation results revealed that eutectic Si
particles segregated along cells were cracked first, but that Al matrix played a role in blocking crack
propagation. Tensile properties and fracture toughness of the cast-forged alloys having
homogeneous distribution of eutectic Si particles were superior to those of the rheo-cast alloy.
Abstract: The present study is concerned with the improvement of hardness and wear resistance in
(Cr3C2,CrB)/carbon steel surface composites fabricated by high-energy electron beam irradiation.
Two kinds of powder mixtures, 50Cr3C2-50STS304 and 50CrB-50STS304 (wt.%), were placed on a
plain carbon steel substrate, which was then irradiated with electron beam. The surface composite
layer of 1.0~1.3 mm in thickness was successfully formed without defects, and contained a large
amount (up to 58 vol.%) of Cr7C3 or Cr1.65Fe0.35B0.9 particles in the austenite or martensite matrix.
The hardness and wear resistance of the surface composites were 2~3 times higher than those of the
steel substrate according to hard particles. Particularly, the surface composite fabricated with CrB
powders showed excellent wear resistance because selective wear of the matrix was considerably
Abstract: Wear resistance of Al2O3-8wt.%TiO2 coatings plasma-sprayed using nanopowders was
investigated. Four types of nanostructured Al2O3-8wt.%TiO2 powders were plasma-sprayed on a
low-carbon steel substrate by using different critical plasma spray parameters (CPSP). The coatings
consisted of completely melted and partially melted regions. The hardness of the coatings increased
with increasing CPSP, while the wear resistance was the highest for the coating sprayed with the
lowest CPSP. The main wear mechanism was a delamination mode in the coating sprayed with the
high CPSP, but was changed to an abrasive mode in the coating sprayed with the low CPSP.
According to this change in the wear mechanism, the wear resistance was the best in the coating
sprayed with lowest CPSP, while its hardness was lowest.
Abstract: Microfracture mechanisms of Zr-based bulk metallic glass (BMG) alloy containing
ductile crystalline particles were investigated by directly observing microfracture processes using
an in situ loading stage. Strength of the BMG alloy containing crystalline particles was lower than
that of the monolithic BMG alloy, while ductility was higher. According to the direct microfracture
observation, crystalline particles initiated shear bands, acted as blocking sites of shear band or crack
propagation, and provided the stable crack growth which could be confirmed by the R-curve
analysis, although they negatively affected apparent fracture toughness. This increase in fracture
resistance with increasing crack length improved overall fracture properties of the alloy containing
crystalline particles, and could be explained by mechanisms of blocking of crack or shear band
propagation, formation of multiple shear bands, crack blunting, and shear band branching.
Abstract: The fracture behavior of ceramic matrix composites (CMCs) was investigated using the
infrared (IR) thermography nondestructive evaluation (NDE) technique during monotonic and
cyclic loadings. The CMCs used for this investigation are continuous Nicalon (silicon carbide fiber)
fiber reinforced calsium aluminosilicate (CAS) glass-ceramics matrix composites. During
monotonic tension and cyclic fatigue loadings, IR camera was used for in-situ monitoring of
temperature evolution, and the temperature changes during testing were measured. Microstructural
characterizations using scanning electron microscopy (SEM) were performed to investigate fracture
modes and failure mechanisms of Nicalon/CAS samples. In this investigation, the NDE technique
and SEM characterization were employed to facilitate a better understanding of damage evolution
and progress of Nicalon/CAS composites during monotonic and cyclic loadings.
Abstract: The aims of this research are to investigate the effect of Sm addition in Mg-Al-Ca alloys on
microstructure and mechanical properties. Sm addition to Mg-5Al-3Ca based alloys results in the
change from dendritic to equiaxed grain morphorlogy and formation of Al-Sm rich itermetallic
compounds at grain boundary and α-Mg matrix. And these Al-Sm rich intermetallic compounds were
dispersed homogeously and stabilized at high temperature. And maximum yield and ultimate strength
value was obtained at Mg-5Al-3Ca-2Sm alloys at elevated temperature because of homogeneous
dispersion of stable Al-Sm rich intermetallic compound at high temperature.
Abstract: Al alloy is used extensively in several fields because specific strength is good and
workability is superior. It is known that If Sc is added to Al alloy, strength is increased and
re-crystallization temperature rises because microstructure becomes fine. The high cycle fatigue
properties of four kinds of Al-Mg-Si alloys without and with only scandium of 0.20 % or with both
scandium(Sc) of 0.20 % and zirconium(Zr) of 0.12% were investigated. The fatigue strength was
determined at R = -1.0 under constant amplitude loading conditions in air. The alloy with scandium of
0.20 % showed a little higher fatigue strength values. The alloy with 0.20 % Sc and 0.12 % Zr showed
highest tensile yield strength and highest fatigue strength. The fine grained Al 6061+0.20Sc+0.12Zr
alloy exhibited a higher resistance against fatigue crack nucleation in comparison to the coarse
grained Al 6061 alloy. The results can be explained mainly with the micro-structural differences
among four alloys. This results are due to the presence of coherent Al3 (Sc, Zr) precipitates and a very
fine sub-grain structure.
Abstract: Fiber-reinforced plastics consist of fibers of high strength and modulus embedded in, or
bonded to a matrix with distinct interfaces between them. Because fiber configuration plays a key role
in determining mechanical strength of fiber-reinforced plastic rods, especially bending strength of
fiber-reinforced plastic rods was measured and simulated numerically in variation with winding
angles. Also, stress distribution in fiber-reinforced plastic rods was simulated numerically under the
condition of constant bending load to fiber-reinforced plastic rods. The measured bending strength of
fiber-reinforced plastic rods in variation with winding angles was different from that of simulated.
The difference between measured and simulated results was due to the effect of shear stresses on the
strength of fiber-reinforced plastic rods.
Abstract: In nano-imprint lithography (NIL) process, which has shown to be a good method to
fabricate polymeric patterns, several kinds of pattern defects due to thermal effects during polymer
flow and mold release operation have been reported. A typical defect in NIL process with high aspect
ratio and low resist thickness pattern is a resist fracture during the mold release operation. It seems
due to interfacial adhesion between polymer and mold. In the present investigation, FEM simulation
of NIL process was carried out to predict the defects of the polymer pattern and to optimize the
process by FEA. To achieve the above mentioned purpose, FEM simulation technique based on
constitutive modeling of polymer with experiments was firstly investigated . Secondly, the
embossing operation in NIL process was investigated in detail by FEM. From the analytical results, it
was found that the non-uniform flow-pattern of polymer and the applied pressure in the embossing
operation induce the cavity and the drastic lateral-strain at the edge of pattern. It was also shown that
the low polymer-thickness result in the delamination of polymer from the substrate. It seems that the
above phenomena cause the defects of the final polymer pattern.