Simulation of Ceramic Grain Growth in Three Dimensions

Microstructural evolutions of ceramic grain growth at atomistic scale were modeled. The simulation was preceded with Monte-Carlo method, using Visual C++ and OpenGL languages. Realistic images in series were monitored both in two d imensions and three dimensions. Simulated image of grain growth in this series i s presented in left figure with N 0=25, r=0.40 nm, α=0.1, T=1 300 ℃, and P 0=50 %. It was seen that the average grain size increases wit h the time of grain growth. It is in good agreement with that of practical BST c eramics. The average grain area versus grain growth time is shown in right figur e. It is clear that the kinetic exponents of grain growth are not constant durin g the process of microstructural evolution. The kinetic exponents are smaller ( m≈0.5) at the early stages of growth and larger (m≈8) at the later sta ges, which are in agreement with reported results.

Dynamic Demonstration of Ceramic Grain Growth in Three Dimensions

Microstructural evolutions of ceramic grain growth we re dynamically demonstrated with 3D graphical display techniques. Based on the p rinciples of grain growth in ceramics, the data of coordination in different ato ms were calculated with Monte-Carlo method at atomistic scale. Realistic images in three-dimension were displayed onto two-dimension monitor by projection, i llumination and atomization, using Visual C++ and OpenGL languages. Different small spheres were used to model different kind of atoms, which filled within a fictitious cube. The radius and coordination for different atoms were then determined according to corresponding ratios by using of perspective projec tion of OpenGL languages. The applications of illuminating, texturizing and at omization techniques enhanced greatly the stereo effect of images.

Effect of Temperature Schedule on the Morphology of SiC Made From Graphite and Silicon Powder

SiC whiskers were synthesized in a coke bed using a two-step heat treatment process.The temperature was held for 3 h at 1 200 ℃ before heating to 1 430 ℃ and holding for 3 h.The morphologies of SiC synthesized by the two-step heat treatment method were much more different from those produced by direct heating to 1 430 ℃.SiC whiskers formed at 1 200 ℃ firstly and grew at1 430 ℃ to obtain a mean diameter about 326 nm,while the SiC grains with a size range from 0.70 to2.30 μm were obtained by direct heating to the target temperature of 1 430 ℃.This was explained by the different formation mechanisms.The result proposes a promising alternative technical process for whisker-reinforced ceramic/refractory composites in-situ during sintering.

Numerical Simulation and Experimental Study of an Ultrasonic Waveguide for Ultrasonic Casting of 35CrMo Steel

To achieve ultrasonic casting of 35 CrMo steel,the waveguide unit for introducing ultrasound into liquid steel was studied numerically and experimentally.The structure and length of the ultrasonic waveguide were optimized by modal analysis.The simulation results showed that a T-shaped waveguide unit matched the vibrational system better than an L-shaped unit.The performance of T-shaped waveguide unit was optimized when the length of the ultrasound radiator was 135 mm.The performance of the T-shaped waveguide unit was investigated in ultrasonic casting experiments,and the effect of ultrasound on the microstructure of 35 CrMo steel was examined.The experimental results showed that the T-shaped waveguide was able to successfully introduce ultrasound into the 35 CrMo melt.In addition,the use of a silicon nitride ceramic radiator avoided high-temperature corrosion in the molten metal.The microstructure of the treated area was significantly refined and equiaxed grains were obtained.The results represented a novel method for ultrasonic casting of steel.

Preliminary Investigation of Preparing High Burn-Up Structure in Nuclear Fuel by Flash Sintering Using CeO_(2) as a Surrogate

The high burn-up structure(HBS)is characterized by the grain size of 100-300 nm and a porosity of up to 20%,which is formed at the rim of the nuclear fuel pellet due to 2-3 times higher local burn-up during the in-pile irradiation.HBS is considered a new potential structure for high-performance fuels.However,it is difficult to prepare HBS by conventional sintering methods.In this study,flash sintering was used to prepare HBS using CeO_(2)as a surrogate for a preliminary investigation.A new experimental configuration for rapid sintering of CeO_(2)pellets was provided,in which the green body can be rapidly preheated and pressure-assisted by the induction heating electrodes.An insulated quartz tube was used as the die for the flash sintered samples,allowing the current to flow through the sample and providing a stable condition for applying an external pressure of approximately 5.3-7.0 MPa during flash sintering process.Using an initial electric field of 141 V cm-1 and holding for 1-7 min at the maximum current density of~98 mA mm^(-2),CeO_(2)ceramics with a grain size of 114-282 nm and a relative density of 75.4-99.7%were prepared.The densification and microstructure evolution behaviors during flash sintering in this new experimental configuration have been discussed in detail.This new experimental configuration may provide a promising approach for preparing UO_(2)ceramics and their HBS.