Investigation On Fabrication And Properties Of Hollow Sphere Cellular Materials Of Ni-Based Superalloy

Ni-base superalloy hollow sphere cellular materials(HSC) were fabricated by powder metallurgy, using INCO-617 alloy powders as raw material, polyvinyl alcohol as binder, polystyrene sphere as pore-forming agent. The influence of powder's properties, binder concentration and liquid-to-solid ratio on coating properties of alloy slurry was discussed, and then the sintering process of HSC was researched. The microstructure and phase constitution of HSC were analyzed by means of scanning electron microscope(SEM) and X-ray diffraction(XRD). The compression test was conducted to investigate the variety in compressive properties of HSC.INCO-617 alloy HSC with porosity ranging from 74.1% to 90.7% were prepared in the experiment. The research on preparation of HSC indicates that good coating properties can be achieved by choosing the atomized fine powders or irregular shape milling powders with appropriate concentration binder. The lower concentration binder, atomized fine powder/milling fine powder with high specific surface energy, higher sintering temperature and longer holding time are conducive to the densification of the cell wall of HSC. The microstructure of HSC comprisesγmatrix, M23C6 type carbides, having high chromium content, and M6C type carbides, having high molybdenum content. With sintering temperature increase and extension of holding time, the size of carbides increase, and the quantity of carbides increase firstly and then decrease. For HSC prepared at same process by using milling powder, the size of carbides become smaller, and precipitations distribute dispersedly.The porosity of HSC is determined by structure parameters and packing of hollow sphere. The results of micro-hardness test and compression test show that the powder sintering extent and microstructure effect mechanical properties of HSC. The HSC fabricated by atomized fine powder have better compression performance, with the densification of cell wall increasing, the compression strength and elastic modulus increase, the stress-strain curves began to appear obvious platform, but with the further increase of sintering temperature and holding time, the stress fluctuations of platform increase due to carbides. At the same density and preparation process, the mechanical properties of HSC with thin cell wall are higher than those of HSC with thick cell wall, and the BCC packing HSC's mechanical properties are higner than those of SC packing. When the hollow sphere packing and preparation process are same, the compression properties of HSC are controlled by choosing different diameter pore-forming agent. The measured values ofσ*/σs are well above the strength of metallic open-cell foam, which is close to the theoretical values for closed-cell foams when sintering temperature is 1230℃. Most of the compressive fractures of superalloy HSC occure at the sintering necks between powders. With cell wall's densification improved, the dense metal cross-section area in the fracture and the plastic deformation volume of cell wall increase. When the sintering temperature is higher than 1150℃, the compressive deformations of HSC are conduct by a layer-by-layer destruction mechanism. HSC have good energy absorption capacity and energy absorption efficiency which exceed 70% before densification stage.The high-melting sandwich structure with adequate strength of the metallurgical interface were fabricated by using milling fine slurry and INCO-617 alloy HSC as bonding layer and core respectively. The deformation mechanism of HSC core sandwich tube is different from tube. In the same compressive strain core make the plastic deformation of outer tube increase, which increase the energy absorption of sandwich structure, remaining the lightweight and high-energy absorption efficiency of HSC. The energy absorption efficiency is above 70% before densification stage. The investigation of fabrication and properties of sandwich panel indicates that lightweight core increase the stiffness of sandwich structure. Because of good interface bonding with enough strength between the HSC core and face, the influence of interface can be neglected in the property test and calculation. The calculated value of loading stiffness and limit load is in good agreement with the theoretical value, showing good prospects for development.