Co-operative Growth Behavior Of Gas Pore And Matrix Of Ordered Porous Cu-Ni Alloys In Continuous Casting

Solid-gas eutectic solidification, also called "GASAR" process, is considered as a new method for producing porous metal. The produced structure is called as "Lotus-type porous metal". Lotus-type porous metal can be made by this process with gas pores distributed evenly and grown along with the direction of solidification. It has not only traditional properties such as light quality, good specific strength, high energy absorption. Compared with conventional porous metal, lotus-type porous metal has many advantages such as lower stress concentration, higher mechanical property and superior capacity of heat conduction. Therefore the lotus-type porous metal has important potential applications in many industrial fields.A computation model for hydrogen solubility in Cu-Ni alloy is developed and the influence of Ni content on the solubility of hydrogen in the alloy is analyzed. It is found that GASAR technology (continuous casting) is applicable to the Cu-Ni alloy. The results show that hydrogen solubility in Cu-Ni alloy increases gradually with the increasing Ni content (or hydrogen gas pressure) when keep the temperature and hydrogen gas pressure constant. The hydrogen solubility in the liquid phase increases to a much higher extent than that in the solid phase.Lotus-type porous Cu-Ni (2,4,6and lOwt.pct) alloys were fabricated by continuous casting technique under a hydrogen gas pressure of0.6MPa at various withdrawal rate. Pore size increase (porosity decrease) gradually with the increase of Ni content when withdrawal rate unchanged. The porosity (and pore diameter) increases gradually with the increasing withdrawal speed, when the Ni content is a constant. The porosity was dependent of the hydrogen gas pressure, but independent of the withdrawal velocity.The effect of mushy zone width of porous Cu-Ni alloy on the pore morphology is analyzed. The results show that the width of mushy zone increases with increasing nickel content or decreasing withdrawal rate. It is considered that the increasing of mushy zone width, not only causes less hydrogen atoms absorbed by the growing gas pore, but also causes the channel that hydrogen atoms from melt into pore is getting far from straight. That is the primary cause of the porosity decreases as the nickel content increases. The change of mushy zone width, not only causes the change of pore structure, but also caused refinement of solidification structure. The growth of pore can be limited via mushy zone width, which can also control the sharp increase or decrease of the number and average diameter of pore.The behavior of pore merger is the main factor for the increase of average pore size along the solidification direction and the non-uniform distribution of pore size. The nucleation of new smaller pores may occur all through the solidification, which causes the non-uniform distribution of pore size. In addition, The interrupt and merger of new pores also occur in the solidification process.