Preparation And Properties Of 316L Stainless Steel Hollow Spheres Aluminum Matrix Composite

As a new type of clean energy,nuclear energy has been used in many fields.However nuclear energy will produce a large number of harmful rays in the using process,and the harmful rays must be shielded.The traditional nuclear shielding materials have many limitations in use,which can not fully meet people’s needs for nuclear protection.And nuclear power equipment will produce a lot of noise during operation.Therefore,it is urgent to study the composite materials with shielding and isolation functions.The development of metal hollow sphere composites provides a new way to solve the problem of new shielding composites.The structural parameters of this composite have a great influence on its shielding and acoustic properties,and the shielding and acoustic mechanism is not very clear.As a result,this paper carries out the research on the preparation,structural design,performance test and corresponding mechanism of 316L stainless steel hollow spheres aluminum matrix composite（S/AC）for the purpose of developing new multifunctional nuclear shielding materials form starting with the preparation process of metal hollow spheres,and obtains the following results.（1）The preparation and sintering process of hollow sphere biscuit are reasonably designed.After sintering,it is found that the diameter and wall thickness of the hollow sphere shrink.With increasing the sintering temperature,the shrinkage of the diameter and wall thickness increases,the porosity of the wall decreases,the microhardness of wall increases,and the compression performance of the hollow sphere improves.The XRD results show that 316L stainless steel powder and hollow spheres are made ofγ-Fe phases.The smaller the particle size of 316L stainless steel,the lower the liquid-solid ratio,the lower the binder concentration and the higher the sintering temperature,the more conducive to reducing the porosity of the wall after sintering（2）A new method for preparing S/AC,vibration assisted die casting,was obtained.The results of micro-morphology and composition analysis show that there is a transition layer between the wall and the matrix formed through the alloying reaction,the thickness and phase composition of the transition layer are related to the holding time of the mold at 710℃.When the holding time is 10 min,the transition layer is a single-layer structure layer composed of a single Fe₂Al₇Si phase with a thickness of 25μm.When the holding time is 20 min,the transition layer is a three-layer structure layer composed of Fe₂₅Al₆₀Si₁₅,Fe₂Al₇Si andγ-Fe phases with a thickness of 35μm.Meanwhile,the matrix is composed of Al,Si,Fe₂Al₄Si and Al₈Si₆Mg₃Fe phases.After solution and aging treatment（540℃,3.5h,water quenching+140℃,1h,air cooling）,the thickness of single-phase Fe₂Al₇Si layer（35μm）is increased by 40%,thickness of three-layer structure layer（53μm）is increased by 51.42%,they are all layer with three-layer structures.（3）With prolonging the holding time of the mold at 710℃,the microhardness of transition layer and matrix increases.When holding time is 10 min,compression performance of S/AC is the best.After solid solution and aging treatment,the microhardness of transition layer,matrix and the compression performance of S/AC are greatly improved.Besides,it is found that the smaller the diameter of hollow sphere and the lower the volume fraction,the better the S/AC compression performance.By observing the changes of morphology during S/AC compression,it is found that the compression deformation process of S/AC belongs to a typical shear deformation process,which can be divided into three stages:elastic deformation,shear deformation and densification.（4）The critical energy of S/AC toγray is 0.834 Me V.Below the critical energy value,the transmission coefficient of S/AC toγray decreases with decreasing the diameter and increasing the volume percentage of hollow sphere.It is revealed that the sound absorption coefficient of S/AC is not only affected by the sintering temperature,diameter and volume percentage of hollow spheres,but also related to whether the sound wave resonates with S/AC in the process of propagation.At resonance,the reflection of sound wave from metal hollow spherical wall is the main factor affecting the sound absorption performance of S/AC.The larger the volume fraction and the smaller the diameter of hollow sphere,the more reflection and the lower the peak value of S/AC sound absorption coefficient.The sound insulation mechanism of S/AC is that the sound wave causes the viscous effect and thermal effect between the air inside the hollow spheres and spherical wall to lose sound energy,and its sound transmission loss decreases with the increase of sintering temperature,volume fraction and diameter of the hollow spheres.（5）S/AC with layered structures（LS-S/AC）is designed and fabricated.The macroscopic observation results show that the layered structure makes the metal hollow spheres evenly distributed and layered in S/AC.During compression,the layered structure can hinder the formation of shear band,cause plastic deformation of S/AC,give play to the supporting role of hollow spheres on S/AC,and improve greatly compression performance of S/AC.Meanwhile the layered structure improves the shielding performance of S/AC toγray with low-energy,reduces the sound absorption coefficient of S/AC and improves the sound transmission loss of S/AC.On this basis,the reasons for the changes of shielding,absorption and sound insulation properties of LS-S/AC are analyzed.