Li Zaijiu

FABRICATION OF LOTUS-TYPE POROUS Cu-Zn ALLOYS WITH THE GASAR CONTINUOUS CASTING PROCESS

A continuous casting technique was developed to fabricate lotus-type porous alloys. Lotus-type porous Cu-xZn (x=2, 6, 10, mass fraction, %) alloys were successfully fabricated by using the continuous casting technique under a hydrogen gas pressure of 0.6 MPa at various transference velocities. The effects of transference velocity and Zn contents on the porosity and pore diameter were investigated. It shows that, for the porous Cu-2Zn alloy, an increased transference velocity will result in a slightly increased porosity and a decreased average pore diameter. Addition of Zn into pure Cu, on the other hand, will result in an increased average pore diameter. Nevertheless, the pore morphology becomes more and more inhomogeneous with increasing Zn content, and the porosity tends to firstly decrease and then increase. Such tendencies are correlated with the Zn content and the corresponding width of the mushy zone.

Influence of Structural Parameters on Tensile Property of Gasar Porous Copper

Abstract Gasar porous copper with various structural parameters was made by metal-gas eutectic unidirectional solidification process. The effects of structure parameters on the uniaxial tensile properties of the porous copper were investigated. The fracture morphologies of tensile samples were studied by scanning electron microscope (SEM). Math models and numerical simulation were performed and confirmed by experimental data. Results show that the tensile properties of porous copper depend on porosity and tensile direction. Ultimate tensile strength of samples with the same porosity whose pore axes are parallel to tensile direction is better than that whose pore axes are perpendicular to tensile direction. For the porous copper whose pore axes are parallel to tensile direction, the ultimate tensile strength decreases linearly with increasing of the porosity, indicating that pores have no stress concentration on matrix. While for the porous copper whose pore axes are perpendicular to tensile direction, the ultimate tensile strength decreases significantly as porosity increases. Ultimate tensile strengths from experiments, models and numerical simulations of two kinds of specimens are consistent well.

Pore Morphology of Lotus-type Porous Silver Fabricated by Gasar Process in Oxygen Atmosphere

Abstract Directional solidification of metal/gas eutectic (Gasar) is a novel process for fabricating porous metals with oriented pores parallel to the solidification direction. Lotus-type porous silver samples with different porosities were fabricated by Gasar apparatus under pure oxygen atmosphere. The effects of gas pressure on porosity, pore nucleation, pore size and distribution were investigated. Results show that the porosity and the pore size in the lotus-type porous silver are significantly affected by the oxygen pressure. The porosity increases with the increasing of oxygen pressure, and the average pore diameter decreases with the increasing of oxygen pressure.

A THERMODYNAMIC MODEL FOR DIRECTIONAL SOLIDIFICATION OF METAL-HYDROGENEUTECTIC

With the thermodynamic analysis on directional solidification of metal-hydrogen eutectic,a theoretical model was developed to predict the effect of the Gasar processing parameters on the pore diameter and interpore spacing.The model was applied for the Gasar porous Cu fabricated by continuous casting process.The average pore diameter and inter-pore spacing decrease as increasing withdrawal rate.The theoretical relationship between the inter-pore spacing l and the withdrawal rate v can be described by a simple equation vl2=B,where B is a constant depending on the melt temperature and hydrogen gas pressure.The model can predict the overall tendency of the experimental results.The deviation between the calculated and experimental values in the case of lower withdrawal rate is considered to be associated with the difference between the real pore structure and ideal pore structure,and the melt convection in the vicinity of solid/liquid interface.