Papers by Keyword: Densification

Abstract: By increasing addition amount of (CrO₃ + Al) subsystem in (B₄C + Ti) system, the solidified TiC-TiB₂ composites with a series of mass fraction of Cr binder were achieved by combustion synthesis in high-gravity field. The microstructures of the solidified ceramics presented a number of fine TiB₂ platelets embedded in TiC grains, Cr-Ti alloy or between TiC grains and Cr-Ti alloy. The increased Cr binder in the ceramic not only brought about the enhanced densification of the ceramic due to fill-up of Cr-Ti liquid in shrinkage cavities between solidified TiC and TiB₂ phases, but more importantly made fine-grained even ultrafine-grained microstructure achieved because of the accelerated nucleation and the decelerated growth of TiB₂ at initial stage of material solidification. As a result of the achievement of fine-grained even ultrafine-grained microstructure along with the enhanced toughneing mechanisms contributed by the refined TiB₂ platelets and the increased plastic phases of Cr-Ti alloy, the solifidied TiC-TiB₂ composite containing 20.7 % Cr binder presented the maximun values of 1045 ± 25 MPa and 21.5 ± 1.6 MPa • m ^0.5, simultaneously, in flexural strength and fracture toughness along with the moderate hardness of 17.5 ± 2.2 GPa.

Abstract: In this paper, plant straw densification technology has been studied. The corn straw was taken as raw material in the experiment. The influences of raw material moisture content, densification pressure and raw material size to the compact process have been studied. The results show that the 13%~18% moisture content of the corn straw is the best scope in compact process. When the raw materials are densified at a pressure of 60MPa, the products have smooth surface, high density. While the pressure continuously increases, the increase of density is not obvious. The raw material size 10~20mm are suitable for densification.

Abstract: A reduced model was used to simulate the CVI process from methane. The scale of the preform was 120mm in diameter and 90mm in height. A random pore model was used to describe the evolution of pores in preform. Parameters such as temperatures and pressures were studied to research the deposition process. Effects of these two parameters are similar but have different impact mechanisms according to the analysis of results. Temperature impacts the reaction rate to improve the efficiency of deposition, while pressure impacts the concentrations of all hydrocarbon and then improves the total amount of carbon which also results in an increase of density.

Abstract: A modified three-dimensional Monte Carlo (MC) model in presence of pores and impurities for three-phase nanocomposite ceramic tool materials is successfully established in this paper. Pore migration by surface diffusion is incorporated into the MC model and it is applied to observe and scientific quantitative characterization of three dimensional microstructure evolution and densification process. Some modifications are applied to the simulation algorithm to improve the computing efficiency. The influence of pores on the particle and impurity loaded grain boundaries is simulated and investigated for the study of grain growth kinetics. The relationship between porosity and density is also analyzed. The results indicate that the higher the porosity is, the lower the density will be.

Abstract: The densification and grain growth during sintering of alumina-zirconia (Al₂O₃ZrO₂) ceramics were simulated using a modified phase field method, which considered simultaneously a density field, a composition filed and orientation fields. The results indicate that the model can capture the main microstructure features in the different stages of sintering. A higher relative green density leads to a higher final density and a larger final grain size in the sintered ceramics. A higher volume fraction of the ZrO₂ phase results in a lower relative density and a smaller final grain size.

Abstract: In this work, the consolidation of different alumina particles via sintering process was conducted to the compacted alumina pellets. This consolidation was also assisted with the sintering aid, MgO to densify the final ceramic structure. Comparison between the influence of additive to the different particles size of compacted alumina by observing the microstructure and physical properties was conducted. The value physical properties and microstructure clearly show that for both particle size of alumina, MgO additive can increase the density value and improve microstructure properties.

Abstract: AZO (Aluminum doped Zinc Oxide) is widely used to produce transparent conductive coatings for liquid crystal displays, flat panel displays, plasma displays, touch panels, and electronic ink applications. The densification behavior of AZO powder is a critical factor related to the design of the compaction process. In this study, the densification behavior of AZO powder during cold compaction has been investigated in order to calibrate the modified Drucker-Prager Cap (DPC) model for FE simulations. A compaction test with a cylindrical die was carried out, and two failure tests were performed: the diameteral compression test and the uniaxial compression test. AZO compacts with various densities from the compact tests were used as specimens for the failure tests. Based on the experimental results, the parameters of the modified DPC model were determined through simple manipulations.

Abstract: A new three-dimensional Monte Carlo (MC) model in presence of pores of microstructure evolution for three-phase nano-composite ceramic tool materials is successfully established to simulate the grain growth during sintering process in this paper. The defect-free microstructure evolution and microstructure evolution in presence of pore are simulated and investigated. The results show that the new MC model can well simulate the grain growth and pores shrinkage during densification process. Compared with defect-free system, the grain growth velocity can be slow down obviously owning to the existence of pores.

Abstract: Hybrid poplar boards were subjected to thermo-mechanical densification combined with heat treatment. Hydroscopicity and hygroscopicity of the treated samples were measured. The results showed that dimensional stability of the samples was influenced by compression set significantly. The higher the compression set, the greater the swelling of the samples. On the contrary, the influence of densification temperature and duration was not significant. Thermal modification significantly reduced hydroscopicity and hygroscopicity of the samples. Both higher treatment temperature and longer holding time resulted in better dimensional stability.

Abstract: Current practice of Dynamic compaction (D.C) depends mainly on field trials, past experience, and empirical equations based on reported records. In this paper, a numerical model is used to study the effectiveness of supplemental drains on densification of saturated dredger fill silty deposits during D.C. Typical numerical results are discussed using propose numerical model.