Papers by Author: Song He Meng

Abstract: The ZrO₂/ZrW₂O₈ ceramic matrix composites have been prepared by the two different processes: (1) ZrO₂ and ZrW₂O₈ powders were mixed directly as raw material, then compacted by cold isostatic pressing under 200MPa, and finally, the ceramic matrix composites with low thermal expansion can be prepared by use of heat-pressing sintering or atmospheric sintering at temperature 1215oC. (2) ZrO₂ (with excess mass) and WO₃ powers were mixed as raw material, then compacted by cold isostatic pressing under 200MPa, and finally, the ZrO₂/ZrW₂O₈ ceramic matrix composites can be made by use of heat-pressing sintering or atmospheric sintering at temperature 1215 oC after ZrW₂O₈ were synthesized by in-situ reaction of ZrO₂ and WO₃ powders at the same temperature. The microstructure, density, ZrW₂O₈ decomposition degree and the thermal expansion coefficient were compared among the sintered samples fabricated by the above two different methods, and affected by the different process parameters. The results show that the ceramic matrix composites with low thermal expansion are really composed of ZrO₂, ZrW₂O₈ and WO₃, and their relative densities are all more than 95%. Compared with the composites prepared by in-situ reaction, the densities, ZrW₂O₈ decomposition degree and the thermal expansion coefficient of the composites made by direct mixing are higher, less and smaller, respectively.

Abstract: The ZrC-20vol.%SiCw ultrahigh temperature ceramics with relative density of 99.2% can be prepared by hot pressing at 1900 oC and 30MPa for 60 min. The mechanical properties and microstructure of the composite were studied. The flexural strength and fracture toughness reaches up to 626.17MPa, 5.03 MPa•m1/2, respectively. SEM analysis shows the microstructure of the ZrC-20vol.%SiCw is homogeneous and SiC whiskers are uniformly distributed around the ZrC grains, which inhibit the ZrC grain growth during sintering. The fracture surface of ZrC-20vol.%SiCw reveals a mixture of intergranular and transgranular failure, and SiC whiskers play a remarkable role in improving the strength and toughness of ZrC matrix. The toughening mechanism of the composite is mainly fine-grain strengthening and whisker pull-out.

Abstract: The two kinds of the Ti-rich (Ti0.8Zr0.2)B2 and Zr-rich (Zr0.8Ti0.2)B2 permutation solid solutions were formed when hot pressed ZrB2 and TiB2 ceramics. On the base of the empirical electron theory (EET) of solids and molecules, the crystal bond energy of the two solid-solutions was calculated by use of Average Atom Model, Average Cell Model and Real Cell Model. In Real Cell Model, the crystal cell parameters were assumed to be unchanged and changed. The calculation results were compared among the three models. The results showed that the general trend about the deviation electrons of B element is consistent except Real Cell Model when the lattice constant is unchanged. Namely, the number of the deviation electrons in TiB2 is more than that in ZrB2.The maximum error of crystal bond energy calculated by the three models is 38KJ/mol and the relative error is less than 2%.The general trend of the crystal bond energy calculated by the three models is monotonically increased similar to the trend of melting point of these materials. Relatively speaking, the calculation of crystal bond energy calculated by Average Atom Cell Model is simpler and more reasonable.

Abstract: Most of fracture processes of carbon/carbon composites (C/Cs) have been found to profoundly affected by their interfacial properties. A fiber-bundle pull-out test is utilized to determine the interface strength between fiber bundles and matrix of two kinds of C/Cs. Pre-fracture observations revealed that amount of voids and gaps existed in the interface, which make the interface strength decreases. The interfacial shear strengths of two kinds of C/Cs were all very low. Post-fracture observations revealed that a shear fracture was successfully induced within the carbon matrices at the loaded fiber bundle interface.

Abstract: According to the dissipation energy principles of plastic Three-dimensional finite element analysis of antiseismic capability of Fe/Zn composite by the finite element software ANSYS. It is the very first time to study responds process of earthquake of metal layer composite. Observed in “Time Hist Postpro” that biggest stress of Fe is lower than the yield intensity of Fe, the biggest stress of Zn is bigger than the yield intensity, Fe supports load and Zn absorbs energy are proved. It is provided to the theories for the system of the new material according to.

Abstract: High temperature oxidation testing was carried out on hot-pressed ZrB2-SiC-graphite composite by using high electric current heating. The composites oxidation behavior was investigated, the temperature of oxidized specimens was above 2000°C. The results found that the UHTC composite was ruptured at oxidized temperature 2055°C. The microstructure of surface and cross-section of posttest samples were investigated by scanning electron microscopy along with energy and X-ray diffraction. The failure mechanism of rupture was also discussed.

Abstract: HfB2-HfC-SiC ultrahigh temperature ceramics (UHTCs) were prepared and characterized in this paper. It is showed that the densities of the HfB2-HfC-SiC reach 98.5% of the theory density. The room temperature compressive properties of the HfB2-HfC-SiC are good, while those at high temperature decrease rapidly. The volume expansion ratio monotonously increases (up to 2.35% at 2300°C) with increasing temperature. Furthermore, with increasing temperature, the average linear expansion coefficient hardly changes, while the instant linear expansion coefficient decreases first, and followed by an increase. The minimum value of the instant linear expansion coefficient is 5.65×10-6/K at 900°C and that of the mean linear expansion coefficient is 7.39×10-6/K at 1340°C. HfB2-HfC-SiC were burned with the plasma arc heater. After 8-second ablation, part of the SiC particles melted and spurted from the composites, and holes appeared.

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.

Abstract: SiC whisker-reinforced ZrB2 matrix ultra-high temperature ceramic were prepared at 2000°C for 1 h under 30MPa by hot pressing and the effects of whisker on flexural strength and fracture toughness of the composites was examined. The flexural strength and fracture toughness are 510±25MPa and 4.05±0.20MPa⋅m1/2 at room temperature, respectively. Comparing with the SiC particles-reinforced ZrB2 ceramic, no significant increase in both strength and toughness was observed. The microstructure of the composite showed that the SiC whisker was destroyed because the SiC whisker degraded due to rapid atom diffusivity at high temperature. The results suggested that some related parameters such as the lower hot-pressing temperature, a short sintering time should be controlled in order to obtain SiC whiskerreinforced ZrB2 composite with high properties.

Abstract: The present study focuses on the dynamic oxidation resistance of five representative ZrB2-SiC based ultra-high temperature ceramics (UHTCs): ZrB2-SiC, ZrB2-SiC-Si3N4, ZrB2-SiC-TiB2, ZrB2-SiCHfB2 and ZrB2-SiC-ZrC using oxyacetylene torch and arc jet testing. The effects of second phase incorporation (Si3N4, TiB2, HfB2, ZrC) on oxidation resistance were compared and analyzed. The mechanism of oxidation based on experimental results and thermodynamic calculations were explored. Some approaches to improvement of oxidation resistance and future directions of UHTC are also presented.