Authors: Qiang Qu, Wen Bo Han, Song He Meng, Xing Hong Zhang, Jie Cai Han
Abstract: ZrB2-based ultra-high temperature ceramics (UHTCs) were prepared from a mixture powder of
Zr/B4C/Si with different ratio via reactive hot pressing. The experimental results showed that the sintering
temperature above 1800°C was necessary for enhancing the activity of the powders and thus improving
the densification of the product. The sinterability and densification properties of ZrB2-based UHTCs
meliorated with the amount of Si increasing. However, many large ZrB2 agglomerates formed when the
amount of synthesized SiC in the product reached 25vol%, which led to decrease the mechanical
property. The composite had highest mechanical properties when the volume ratio of ZrB2: SiC: ZrC was
73.86:20:6.14, and its flexual strength and the fracture toughness were 645.8MPa and 5.66MPa·m1/2
respectively. The microstructure investigation showed the in-situ formed SiC and ZrC were located in the
triple point of ZrB2 grains with a size less than 3μm.
1737
Authors: Gui Song Wang, Lin Geng
Abstract: The two (Al2O3+TiB2+Al3Ti)/Al composites were fabricated from Al-B2O3-TiO2 and
Al-B-TiO2 raw powders by reactive hot pressing, respectively. The microstructure of in situ two
composites was analyzed by OM, SEM and TEM. The results showed that coarse Al3Ti blocks with
several tens of micrometers size were formed during hot pressing. The equiaxed Al2O3 particulates
and hexagonal TiB2 particulates with finer sizes were formed in the composites simultaneously. The
microstructure formation mechanism of (Al2O3+TiB2+Al3Ti)/Al composites were discussed. The
results showed that Al2O3 reinforcements were formed on the surface of TiO2 or B2O3 powder and
TiB2 particles were formed on B or B2O3 powders. The formation of coarse Al3Ti block is result
from continuous diffusion of Ti in liquid Al during reactive hot pressing. In addition, there are fine
Al3Ti precipitates exist in the composite fabricated from Al-B-TiO2 powders. This contributes to
the improved mechanical properties in terms of yield and ultimate stresses and Young’s modulus of
the composite.
1439
Authors: Peng Chao Kang, Gaohui Wu, Zhong Da Yin
Abstract: MoSi2-SiC precursor powder has been synthesized via the mechanical alloy method with
the elements Mo, Si and C powder. The SiC/MoSi2 composites with different SiC volume fraction
have been prepared by reactive hot-pressing the precursor powder at 1350 °C. There is a significant
increase in the fracture toughness due to addition of SiC reinforcement. However, the intermediary
ternary phase exists in this system—namely, Mo5Si3C, Nowotny phase, which has negative effect on
the fracture toughness, and can be eliminated through high temperature treatment at 1600 °C for 2 hrs.
1326
Authors: Chang Chen, Ting Yu, Jian Feng Yang, Ji Qiang Gao, Zhi Hao Jin, Koichi Niihara
Abstract: Based on low-temperature hot-press sintering and rapid thermit reaction, heat-resistant
metal matrix composites with nano-ceramic reinforcement were prepared via reactive hot pressing.
According to XRD, the composites comprised predominantly of (fcc) Cr0.19Fe0.7Ni0.11, (fcc) Fe-Cr
and alumina at 700°C through the highly-exothermic thermit reaction between the starting powders.
Three-point bending strength, fracture toughness, Vickers hardness and relative density increased
with the increase of hot-press sintering temperature and holding time. The improving mechanical
properties may be explained by increasing of content of (fcc) Cr0.19Fe0.7Ni0.11. SEM analysis showed a
microstructure consisting of equiaxial granules at 700°C for 1 h and a uniformly dispersed network of
very fine grains at 700°C for 2 h. It is considered that, in the reactive hot-pressing process, Al atoms
diffused into the metal matrix (Fe2O3, Cr, Ni) sites and formed Al2O3 and Fe-Cr-Ni matrix. Such a
technique offers the possibility of synthesizing heat-resistant metal matrix composites with
nano-ceramic reinforcement materials at considerably lower temperature.
87
Authors: Dominique Gosset, Mickaël Dollé, Fabrice Legendre, François Guillard
Abstract: In the frame of the development of new nuclear reactors (Gen-IV project), materials able
to withstand very high temperatures are required. Among the components of the cores, the transition
metal carbides could be favourably considered as fission products barriers or inert matrix for the
fuel. They are highly refractory, have good neutron properties and fission products retention.
Unfortunately, first they are brittle and second the elaboration process of bulk materials requires
drastical conditions (temperature, pressure). We have then undertaken the comparison of different
materials to investigate the potentialities of nano-sized microstructures for the improvement of the
mechanical properties and to determine the impact of different elaboration routes to obtain high
density articles. The elaboration process of the nano-sized powders is presented elsewhere [M.
Dollé et al., this meeting]. Here, we compare different sintering processes (uniaxial hot-pressing,
spark plasma sintering) and we present a new process able to produce high density zirconium
carbide articles with soft conditions. We show that the sintering of co-ground zirconium and
graphite powders lead to high density, homogeneous, low grain-size materials at temperatures as
low as 1500°C. At the contrary, the nano-powders appear to be more difficult to densify that
classical micro-sized powders.
629
Authors: H. Tsuda, T. Ohtsuka, Hiroshi Mabuchi, K. Morii
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