Study On Pore Morphology Of Regular Porous Iron-based Material

Metal-gas eutectic directional solidification technology(Gasar)is the main method to prepare regular porous metals,which is based on the difference of gas solubility between the solid and liquid phases of the metal.The gas is saturated in the liquid phase of the metal and forms pores after directional solidification.Compared with the traditional porous preparation method,the porous materials prepared by Gasar technology have better mechanical properties.There is a big solubility difference of nitrogen in the solid and liquid phases of iron-based materials.Therefore,in this paper,nitrogen is used as the working gas,porous iron-based materials are prepared by zone melting technology,and the effects of zone melting process parameters on the porosity and pore morphology of porous iron-based materials are studied.On the basis of obtaining the maximum porosity,alloy elements Ni and Mn are added to iron-based raw materials.The effects of alloying elements on porosity and pore morphology were studied.The effects of zone melting process parameters and alloying elements Ni and Mn on the solubility of nitrogen in iron-based materials were studied.The zone melting process in this paper is nitrogen pressure and solidification rate.The experimental results show that the porosity changes significantly under different nitrogen pressure or solidification rate.The porosity of porous iron-based materials increases with the increase of nitrogen pressure.When the nitrogen pressure reaches1.0 MPa,the porosity is the highest,which is 19.8%.With the decrease of solidification rate,the porosity increases first and then decreases.When the nitrogen pressure is 1.0 MPa and the solidification rate is 10 mm/min,the porosity is the highest,which is 34.7%.The effect of process parameters on porosity and pore morphology is attributed to the solubility difference of nitrogen in the iron-based materials.The higher the nitrogen pressure is,the greater the solubility difference of nitrogen in the solid and liquid phases of the iron-based materials is,and the porosity increases.Under the same nitrogen pressure,reducing the solidification rate can also increase the solubility difference,and thus increase the porosity.Based on the diffusion theory,the change of pore morphology in the prepared porous iron-based material was explained.The addition of Ni decreases the solubility of nitrogen in the liquid phase of Febased materials,and increases the solubility of nitrogen in the solid phase of Fe-based materials,which leads to the decrease of the solubility difference of nitrogen between the solid phase and the liquid phase,and decreases the porosity of porous Fe-based materials.At the same time,the pore diameter increases and the number of pores decreases.The addition of alloying element Mn can increase the solubility of nitrogen in both solid and liquid phases of iron-based materials,and slightly increase the solubility difference of nitrogen in both solid and liquid phases of iron-based materials,but the addition of alloying element Mn can reduce the pore diameter and the number of pores,resulting in the decrease of porosity.