Structure And Mechanical Properties Of Porous Gasar Copper (alloy) Pores

Gasar, also called "unidirectional solidification of metal-gas eutectic", which is based on the gap of gas solubility between liquid and solid metals, is a revolutionary process for fabricating porous metal. Compared with the randomly distributed pore structure of traditional sintered or frothed porous metals, the pores in Gasar porous metals are aligned one direction. This resulted in an unique combinations of physical and mechanical properties such as higher mechanical property and superior capacity of heat transmission for Gasar porous metals. Therefore, this kind of porous metal has important potential applications. The pore structure parameter is significant factor that impact the porous metals properties. In order to quantitative control the pore structures, the appropriate studies have been carried out by many researchers. Few researches are systematically made on the pore nucleation and growth processes and their impact on the pore structures, and no researches have been made on the prediction model obtained from the thermodynamic analysis on directional solidification of metal-hydrogen eutectic. The other is that the influence of alloying on pore structure of Gasar porous metal has not been further researched. In addition, the research concerned the mechanical behavior of Gasar porous metal under the recombination action of pore structure and loading direction is still deficient. This thesis will be concentrated on these three aspects.By use of the developed Gasar mould casting apparatus, porous Cu samples with different pore structure parameters have been fabricated. Based on the law of mass conservation, a theoretical formula was proposed for calculating the porosity in Gasar porous Cu. Furthermore, through a deep analysis of the process of pore nucleation and growth, find out the mechanism of how the process parameters (gas pressure and degree of superheat) influence the pore structure.In order to quantitative control the pore structures of Gasar porous metal, a Gasar continuous casting technique was developed to fabricate porous metal. A lot of porous Cu samples were fabricated under different hydrogen pressures and withdraw rates. 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 inter-pore spacing. 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.Gasar porous Cu, Cu-Zn and Cu-Ni samples with different cross-sections (φ15mm and80×12mm) have been fabricated by using the continuous casting technique under a hydrogen press of0.6MPa at various withdraw rates. The influences of Zn and Ni contents on the pore structure and morphology were investigated. The change of pore structure and morphology of porous alloy samples is primarily dependent on the solidification mode (planar, cellular, columnar dendritic, equiaxed dendritic) and the width of mushy zone, which are controlled by the alloying element contents.The anisotropic mechanical properties of Gasar porous Cu under the recombination action of pore structure and loading direction was studied. The results shows the mechanical behaviors depend on the porosity and the loading directions.