Investigation On Fabrication Process Of Three-dimensional Continuous Porous Metal Materials By Vapor Phase Alloying-dealloying

Porous metal materials have many advantages compared with traditional metal materials,and are widely used in aerospace,energy storage,transport,etc.However,the traditional dealloying fabrication process has certain shortcomings,such as chemical contamination,and structure coarsening during liquid metal dealloying.As an emerging dealloying process,vapor phase dealloying has attracted the attention of researchers in recent years.The more active atoms are removed on the basis of the saturated vapor pressure difference of alloy components at a certain temperature,and the remaining atoms form a porous structure by diffusion and rearrangement.Based on the above considerations,this thesis proposed a new route for fabrication of porous metal materials by vapor phase alloying-dealloying.The solid metal was transformed into a porous material through the vapor phase alloying and dealloying process of the vapor phase metal(Zn)and the solid metal.The microstructure and mechanical properties were characterized and analyzed.We also studied the influence of vapor phase alloying time and temperature on the microstructure of the porous layers.(1)A set of vapor phase alloying-dealloying equipments were designed and built by ourselves,and porous Cu foil with a mean ligament size of 4.17±1.53 μm was fabricated.The Zn was tracked in the whole process by means of scanning electron microscope(SEM),energy dispersive X-Ray spectroscopy(EDX),and X-ray diffraction(XRD),which confirm the evolution of phase and composition during the alloying-dealloying process,and the feasibility of the vapor phase alloying-dealloying process for fabrication of porous Cu foils.In addition,three-dimensional continuous porous Cu foil materials using the vapor phase alloyingdealloying process were obtained successfully with different thicknesses(0.05 mm,0.1 mm,0.2 mm,0.3 mm,and 0.5 mm)and different sizes(20 × 5 × 0.1 mm3 and 200 × 40 × 0.1 mm3).The mechanical properties of the pristine Cu foil and the porous Cu foil were further tested.It was found that the elongation at break,tensile strength and hardness of the porous Cu foil decrease to a certain degree with the decrease of density causing by three-dimensional continuous porous structure.(2)Three kinds of Cu-Ni alloy foils(Cu9Ni1,Cu7Ni3 and Cu5Ni5)were fabricated by vacuum sealing-melting-rolling process,and porous Cu9Ni1,Cu7Ni3 and Cu5Ni5 foils were fabricated by vapor phase alloying-dealloying process.The mean ligament sizes of the porous Cu9Ni1,Cu7Ni3 and Cu5Ni5 alloy foils were 1.95±0.47 μm,1.03 ± 0.33 μm and 0.72 ± 0.20μm,respectively through the microstructural characterizations.With the increase of the Ni content,the ligament size was obviously refined.In particular,the mean ligament size of porous Cu5Ni5 alloys was reduced to the submicron scale.And the elongation at break,tensile strength and hardness of the porous Cu-Ni alloys are improved with the increase of Ni content through the mechanical properties test.According to the analysis,this is related to the structure scale(average ligament size)of the porous Cu-Ni alloy and the Ni content in the alloy.(3)Aiming at the problem of easy oxidation of metal Ti at high temperature,on the basis of the above work,the vapor phase alloying-dealloying process and device air tightness were further improved.The porous Ti-6Al-4V alloy(TC4)foil with a mean ligament size of 0.70 ±0.17 μm and the porous Ti foil with a mean ligament size of 0.98 ± 0.26 μm were fabricated.The influence of vapor phase alloying temperature and time on the alloying process of Ti-based materials was studied,and self-supporting porous TC4 and Ti foils with different porous layer thicknesses were fabricated by further vapor phase dealloying process.The results show that with the increase of vapor phase alloying temperature and time,the thickness of the porous layer of TC4 and Ti foils will also increase.That is,by changing the process parameters such as temperature and time,the characteristic size of the porous metal material can be regulated(such as ligament size,porous layer thickness),and their structural and functional properties can be further regulated.