Papers by Keyword: Solidification Velocity

Abstract: In this article, a three-dimensional time-dependent model describing the evolution of single pore during the solid/gas eutectic unidirectional solidification process (also called gasar process) was established. The mass transfer, bubble nucleation, pore growth and interruption were all considered in this model. The pore structure of lotus-type porous copper and aluminum were simulated under different solidification velocities. The results indicate that: coupled growth of both solid and gas phases can be achieved in a proper range of solidification velocities. The solidification velocity for Cu-H₂ system is dozens of that for Al-H₂ system when the pore diameter is similar to each other. The differences of the solute distribution coefficient (k₀), diffusion coefficient (D_L) and the constant of solubility of hydrogen (ξ(T_m)) in the melt are regarded as the main reasons of the big discrepancy of solidification velocity between Cu-H₂ and Al-H₂ systems.

Abstract: Lotus-type porous silicon is a promising micro-channel heat sink material in cooling of high powered electronic devices. Lotus-type porous silicon with elongated pores has been successfully fabricated by unidirectional solidification at different velocities. The average pore diameter and inter-pore spacing all increase whether along the height direction of the ingot or with increasing the thickness of graphite sheet (lower solidification velocity). The calculated porosity is in good agreement with the experimental results which almost keep as constant at different solidification velocities. The penetration ratio or the pore length increases with decreasing solidification velocity. The bigger pores are more likely to grow longer than smaller ones. In addition, the microstructure observation shows that the pores mostly distribute at the grain boundaries.

Abstract: The requirements are getting higher and higher at the vehicle industry area first of all at cylinderhead casting. The customers would like to buy high performanced engines with low consumption.The brandnew trend in the car industry area is the „downsizing” nowdays. It means that the cylinderhead capacity is low but the accessible performance is much bigger than earlier. The problem is that the wallthickness of the cylinderheads will be less. That is the reason why the strength properties and requirements are getting stronger.

Abstract: Lotus-type porous metals with low thermal conductivity are fabricated by continuous zone melting technique, which possess directional elongated pores. The porous metals have been able to be fabricated through the conventional casting method by utilizing the solubility gap between solid and liquid in pressurized gas atmosphere. However, there is a shortcoming that the pores are coarsened in the part farther from the chill plate in the ingot. In order to overcome such a shortcoming, we developed the continuous zone melting technique and successfully produced the lotus-type porous metals with even low thermal conductivity such as stainless steel and superalloys. Furthermore, from the viewpoint of mass production with low cost, we invented novel ”continuous casting technique”. The molten metals dissolving gas are solidified continuously by passing through the mold cooled with chiller and thus, lotus-type porous metal plate as long as one meter was produced for short time. Sufficient uniformity of the porosity and pore size was obtained in such long porous ingots. This technique is prospective method for commercial mass production.