Study On The Pore Structure And Compressive Properties Of Lotus-Type Porous Copper Fabricated By Zone Melting Technique

Unidirectional solidification of Metal-gas eutectic(Gasar)is a new process for fabricating porous metal materials.The porous metal material fabricated by Gasar process has cylindrical pores arranged along the direction of solidification.As the pore structure resembles the root of lotus,the porous materials are often referred to as“lotus-type”porous materials.The special pore structure of lotus-type porous metal material makes it having many special properties,and thus has many potential applications in the field of both structural and functional materials.The porous metal material with uniform pore distribution can be fabricated by zone melting technique.The zone melting has the advantage of having a constant solidification rate during the solidification process,by controlling the transference rate.And there is no requirement for the use of crucible and mold in the zone melting process,thus the contamination of the melt can be avoided.In this study,lotus-type porous copper was fabricated by zone melting technique under different gas pressure(hydrogen and argon pressure).The effects of gas pressure and transference rate on the pore structure and morphology of lotus type porous copper were analyzed.The results showed that at the hydrogen pressure of 0.1 MPa to 0.4MPa,with the increase of hydrogen pressure,the porosity increases first and then decreases.When the hydrogen pressure is 0.2MPa,the porosity is 19.52%as the largest.The average pore diameter decreases from 0.89mm to 0.42mm,and the distribution range of the pore diameter gradually narrowed,the uniformity of pore size increased.And the pore number density increases from 27.97/(100mm2)to 94.79/(100mm2).In the case where the total pressure of the gas is 0.4MPa and the hydrogen partial pressure is 0 to 0.4MPa,with the increase of the partial pressure of hydrogen,the porosity increases from 0 to 16.88%.The average pore diameter increases from 0 to 0.42mm,and the distribution range of pore diameter is widened,the uniformity of pore size decreases.The pore number density decreases first and then increases,and when the hydrogen partial pressure is 0.3MPa,which is 62.79/(100mm2)as the smallest.When the hydrogen pressure is 0.2MPa,with the transference rate increases from 10 mm·min-1 to 30 mm·min-1,the porosity increases from 9.88%to 23.44%.The average pore diameter decreases from 0.81mm to 0.64mm.And the pore number density increases from 16.06/(100mm2)to 57.88/(100mm2).The pore diameter distribution is hardly affected by the transference rate.The compressive properties of lotus-type porous copper were measured at room temperature.The influence of the pore structure parameters(porosity and average pore diameter)on the compressive properties in the direction paralleled to the pore growth direction of lotus-type porous copper was analyzed.The results indicated thatWith the increase of the porosity from 5.61%to 24.11%,the slope of the compressive stress-strain curve of the lotus-type porous copper in the zone is gradually reduced,and its compressive yield strength decreases from 25.63MPa to 12,61MPa,the unit volume absorption is gradually reduced from 39.53 MJ·m-3 to 29.38 MJ·m-3,Young's modulus decreases from 2.76Gpa to 1.10GPa,the densification strain increases from 40.11%to 44.76%,and the ability of the lotus-type porous copper to resist plastic deformation decreased with the increasing of the porosity.With the average pore diameter increased from 0.52mm to 0.61mm at a constant porosity(13%),the compressive yield strength,the densification strain,the unit volume energy absorption and the Young's modulus were all increased.And the ability of the lotus-type porous copper to resist plastic deformation was decreased.The main deformation mode was the bending deformation and folding deformation of the pore wall under the compression load in the process of compression deformation.