The Pore Growth And Coalescence Behavior In Lotus-Type Porous Copper Alloy

Directionally solidified lotus-type porous material is a porous material preparation technology which developed in the past 20 years.The porous material of lotus-type has a cylindrical structure of pores,which shows many excellent properties.For the pore structure of lotus-type porous materials,the pore structure parameters were mainly adjusted by changing the process parameters in the past,but the specific dynamic process of pore growth has not been studied in detail.This is mainly due to the opacity of metal materials,it is always a difficulty to directly observe the growth process of pores in metal.In order to overcome this difficulty,this paper adopts directional solidification method to prepare lotus-type porous Cu-Cr and Cu-Zn alloy,and then reproduces the dynamic process of pore growth by X-ray tomography and 3D reconstruction technology,which provides a possibility for studying the growth mode and process dynamics of pore growth in metal melt.At the same time,the influence mechanism of alloying elements on the process of pore growth was discussed by means of thermodynamic calculation.The main conclusions of this paper are as follows:(1)The growth methods of pores are divided into three types: single-grown pore,interacting pore,and coalescing pore.(2)For a single growth of pore,it can be divided into two types: stable growth of pore(the average diameter of pore can reach 880?m,the growth time lasts 48 s,or more);non-stable growth of pore(the average diameter of the pore is less than 330?m,the growth time lasts 4s,Or even less).The addition of Cr element prolongs the growth process of Spherical growth stage.For interacting pores,small pore are more likely to disappear around the big pore.For the two pores merged,their lengths are obviously different.The merger process is divided into three stages: before coalescing,during coalescing,after coalescing,and during coalescing.The pore coalescing speed is fast and the duration is short.The addition of Cr prolongs the process of pore fusion and makes the process of pore fusion slow.(3)The growth of pores leads to the segregation of Cr and Zn atoms,which leads to the enrichment at the gas-liquid interface(pore wall).Thermodynamic calculations show that the concentration of Cr and Zn atoms results in a decrease in the gas-liquid interfacial tension,and the higher the alloy content,the lower the gas-liquid interfacial tension.The decrease of gas-liquid interfacial tension reduces the resistance of pores growth and thus promotes pores coarsening.(4)For the lotus-type porous porous Cu-Cr alloy,as the Cr content increases,the solubility difference of hydrogen in the metal solid-liquid phase increases,causing porosity to increase.In addition,with the increase of Cr content,the width of the mushy zone of the alloy increases,reducing the overflow of hydrogen,increasing the amount of hydrogen diffusing into the pores,and also causing the increase of the porosity.