Abstract: The microstructure characteristics of the spray-formed and melt-spun Al85Nd5Ni10 and
Al89La6Ni5 alloys were studied. The spray forming process was demonstrated to produce a bulk
scale hybrid composite consisting of amorphous and nanostructured phases directly without the
need of an amorphous precursor. The spray-formed Al89La6Ni5 deposit (~1 mm in thickness) were
partially amorphous, and the amorphous phase came from the undercooled liquid droplets upon
deposition. The as-spray-formed Al85Nd5Ni10 deposit (~20 mm in thickness) was completely
crystallized due to the devitrification of the retained amorphous phase to nano-scale secondary
crystals upon deposition. Primary crystals (~1 μm) are dispersed uniformly in the bulk
spray-formed amorphous/or partial amorphous composites and many distinctive deformation twins
also are observed in the crystals, however, not twins found in the corresponding completely
devitrified ribbon. This is mainly because of the stirring and impacting force offered by high
velocity droplets during spray forming and the mismatch of thermal expansion coefficient between
primary crystals and adjacent amorphous matrix.
Abstract: The effects of high-energy ball milling on SiC powders were studied using a planetary
apparatus. Conditions to obtain nanostructured SiC powders with an average crystallite size of 4 nm
were determined and powders were characterized by XRD, SEM and TEM analyses. This process
was applied to prepare fine powders leading to dense SiC ceramics by sintering at 1900oC for 30
minutes under 30 MPa in argon.
Abstract: The nano-sized silica particulates reinforced poly(ether ether ketone) (PEEK) composites
were fabricated by means of simple compression molding technique. The nano-sized silica,
measuring 30 nm in size, was firstly modified by surface-pretreatment with stearic acid. The
thermomechanical properties of the resulting PEEK/SiO2 nanocomposites were measured using
dynamic mechanical analysis (DMA) and thermal mechanical analysis (TMA). The TMA results
show that the coefficient of thermal expansion (CTE) becomes lowered when the content of the
nanosilica increases. Furthermore, the CTE of the modified-silica filled PEEK nanocomposites
shows higher CTE values, as compared with those of the unmodified counterparts. The dynamic
modulus of the PEEK nanocomposites shows over 40% increment at elevated temperatures from
100-250oC, indicating the apparent improvement of elevated temperature mechanical properties.
Abstract: In the present study, Ti50Cu28Ni15Sn7 metallic glass and its composite powders
reinforced with 4~12 vol% of SiC additions were successfully prepared by mechanical alloying.
The as-milled Ti50Cu28Ni15Sn7 and composite powders were then consolidated by vacuum hot
pressing into disc compacts with a 10 mm diameter and thickness of 2 mm. The structure of the
as-milled powders and consolidated compacts was characterized by X-ray diffraction. While the
thermal stability was examined by differential scanning calorimeter. In addition, the mechanical
property of the consolidated bulk metallic glass and its composite was evaluated by Vickers
microhardness tests. In the ball-milled composites, initial SiC particles were homogeneously
dispersed in the Ti-based alloy glassy matrix. The presence of SiC particles did not dramatically
change the thermal stability of Ti50Cu28Ni15Sn7 glassy powders. BMG composite with submicron
SiC particles homogeneously embedded in a highly dense nanocrystalline/amorphous matrix was
successfully prepared. A significant hardness increase with SiC additions was noticed for
consolidated composite compacts.
Abstract: Materials characterization is a crucial issue in the development and application of new
materials. Materials characterization aims to mine and acquire characteristic information and their
evolution in the materials. It mainly includes three important topics which are microstructural
characterization, properties characterization, and environmental degradation. In this paper,
characterization techniques about these topics were discussed for C/SiC composites and a
characterization system was preliminarily established. All these characterization research and their
results further the better understanding of the relationship between microstructure and properties
and of the failure mechanisms in the C/SiC composites.
Abstract: Copper and 2024 aluminum alloy were melt-infiltrated into porous β-SiC to form SiC/Cu
and SiC/Al composites. The porous β-SiC was prepared using Moso bamboo as the bio-template
and had structural characteristics of bamboo. The Cu infiltration occurred as low as 1100°C and
became significant at 1200°C. After infiltration at 1300°C for 4 h, there was still ~5 % of residual
porosity. For the composites with low degree of metal infiltration, the samples fractured like the
bamboo-structured porous SiC. For the composites with high degree of infiltration, the sample
behaved like monolithic copper. In the infiltration of Al alloy, infiltration occurred at 900°C. Higher
Infiltration temperatures would result in significant formation of Al4C3, which gradually
decomposed in air.
Abstract: Carbon fiber reinforced silicon carbide matrix composites (C/SiC) are promising candidate
materials for high-temperature structural applications. However, in oxidizing environments the two
main constituents, that is, carbon fiber and pyrolytic carbon interphase which bears and transfers
loads respectively are susceptible to deplete rapidly for oxidation. In this paper, the oxidation
behavior of carbon fiber and pyrolytic carbon were investigated by simulating environmental
experiments and scanning electron microscopy. The reactivity discrepancy in the carbonaceous
constituents and in the different zone of carbon fiber was discerned. After oxidation, the morphology
of carbon phase broken before oxidation were compared with that of those broken after oxidation.
Based on the microstructural model, the contrast results of morphology were well interpreted from
the reactive preference and selectivity.