· 96 · IMP & HIRFL Annual Report 2018

5 - 10 Synthesis and Characterization of ZTA-TiC Composite

Fabricated by Spark Plasma Sintering

Zhu Yabin, Liu Chao, Tai Pengfei, Chai Jianlong, Guo Yawei, Li Shufen and Wang Zhiguang

ZTA-TiC composite, which possesses attractive mechanical properties, good electrical and thermal conductivities,

has attracted significant attention because of its potential applications in many aspects, such as bearing components,

cutting tool inserts, valve seats, pump components, oxygen sensors, dies and prosthetic components applications.

The commercial α-Al2O3 (99.99%) with average particle size of 30 nm YSZ (3 mol% Y2O3 stabilized ZrO2 99.99%)

and TiC (99%) both with average particle size of 50 nm were used as starting powders. The α-Al2O3, ZrO2 and

TiC was mixed in different ratios and mechanically milled in a planetary ball mill. Alcohol as the milling media was

added into the powder mixture and was wet-mixed by ZrO2 grinding ball milling in a zirconia jar for 20 h. After

being mixed, dried and sieved, the powders were loaded into the cylinder dies and sintered by the spark plasma

sintering (SPS) apparatus in vacuum (<10 Pa) at temperature of 1 400 ℃, with a pressing pressure of 40 MPa.

The holding time was 10 min. Before examination, the surfaces of the samples were ground to remove the graphite

layer.

The density of as-sintered samples was measured by means of the Archimedes’ method. The result shows that

the relative densities of all samples are higher than 98%. The composition of the samples was analyzed using XRD,

as shown in Fig. 1. The XRD pattern shows presence of only three phases (corundum, yttria-containing zirconia

and titanium carbide), which indicates that no reaction has taken place during milling and sintering. Moreover,

with the TiC content increases, the relative intensities of TiC diffraction peaks (e.g. 36.1◦ and 41.7◦) increase, while

the relative intensities of Al2O3 (52.6◦) and ZrO2 (50.3◦) diffraction peaks decrease.

Fig. 1 (color online)XRD pattern of composites with different TiC contents.

The SEM image of polished surface is shown in Fig. 2(a). One can see that the microstructure displays a

homogeneous distribution of TiC particles within the ZTA matrix. Fig. 2(b) shows the fracture surface SEM

graphs of TiC(20 v.%)-ZTA sample. It gives that the fracture mode of ZTA-TiC composites combines intergranular

and transgranular behaviors.

The thermal conductivity of the composites with different TiC contents was measured by a laser conductometer.

The results of thermal conductivity of composites varying with temperature are shown in Fig. 3. It is found that

the thermal conductivity is strongly dependent on the volume fraction of TiC. Sample which contains 10 vol.% TiC

shows an electrical conductivity of 11.5 W/mK at room temperature, while the sample which contains 25 vol.% TiC

is 14.9 W/mK. In addition, the thermal conductivity decreases significantly with the increasing temperature. For

TiC(10 v.%)-ZTA and TiC(25 v.%)-ZTA, the thermal conductivity decreases to 5.2 and 8.9 W/m·K respectively as

the increasing temperature to 1 200 ℃.

Fig. 4 shows the relative densities and fracture toughness of ZTA-TiC ceramics as a function of TiC content.

The decrease in relative density from 99.0% to 98.3% is due to the addition of fine TiC particles. The ZTA

matrix and TiC additive show different shrinkage characteristics during sintering process. Thus, the distribution of

TiC particles induces tensile stress into the sintering samples and influences the densification rate. Moreover, the

distribution of TiC particles slows down the diffusivity of grain boundary. It is well known that the diffusion along

grain boundaries is the predominant mechanism of material transfer during solid-state sintering. TiC particles,

2018 IMP & HIRFL Annual Report · 97 ·

which located at grain boundaries, prolong the diffusion path along grain boundaries. In addition, the extension

of diffusion path is in proportional to the diameter of TiC particles. The slower diffusion of atoms/vacancies along

the interfaces between the ZTA matrix grain and TiC particles also leads to the decrease in the sample densities.

Fig. 4 also shows that the fracture toughness increases from 5.26 to 6.26 MPa·m1/2 when the TiC content increases.

This is due to that the fracture toughness can be improved by increasing Young’s modulus by means of the addition

of high-modulus particles into the oxide. Therefore, the addition of high-modulus TiC nanoparticles into the ZTA

matrix increases the Young’s modulus of ZTA-TiC ceramics contributing to the enhancement of KIC.

Fig. 2 (color online) SEM micrographs of polished surface (a) and fracture surface (b) of the sintered TiC(20 v.%)-ZTA sample.

Fig. 3 (color online)Thermal conductivity of compositeswith different TiC contents varying with measuringtemperature.

Fig. 4 (color online)Relative densities and fracturetoughness of ZTA-TiC ceramics varying with the TiCcontent.

5 - 11 Study on the Swelling of SiC Fibers Irradiated by Ions

Niu Lijuan1,2, Wang Zhiguang1 and Sun Jianrong1

( 1 Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730070, China;2 Graduate University of Chinese Academy of Sciences, Beijing 100049, China )

SiC fibers owing to their outstanding properties have been intensively investigated and applied to be the rein-

forcements in ceramic matrix composites (CMCs), which have been recognized as the promising structure materials

of harsh environments, such as aerospace, aviation, fission and future fusion reactors[1]. In these environments the

materials can withstand intense radiation and high temperatures. However, the properties of SiCf/SiC composites

after irradiation have changed, which seriously affected the safe operation of the device. The properties of compos-

ites depend on the properties of each component. It is necessary to study the performance of SiC fiber under the

irradiation.

The experimental samples were KD-II SiC fiber bundles (National University of Defense and Technology, China)

using the organic precursor conversion method. The fibers mainly underwent four steps of synthesis, melt spinning,