Preparation And Properties Of Metal-Ceramic Double Shell Hollow Sphere/Aluminum Matrix Composites

With the demand of carbon peaking and carbon neutrality,the manufacture of lightweight,green and intelligent ships is a current new hotspot in the development of ship field.Choosing high-strength and lightweight materials in ship manufacturing can effectively reduce the weight of the hull,improve service performance and realize lightweight of marine materials.Aluminum alloy,due to its excellent properties such as low density,high strength,and corrosion resistance,has important applications in lightweight shipbuilding materials.However,aluminum alloy has a high thermal conductivity,making it difficult to adapt to the thermal insulation requirements of the ship’s power system and related compartments.To meet the dual needs of aluminum alloy in terms of mechanical properties and thermal insulation functions,material structure and performance design of aluminum alloy itself is currently a research hotspot.In recent years,the developed hollow sphere aluminum matrix composites have provided a new way to achieve the integration of structural and functional properties of aluminum alloys.Based on this,this paper started from the lightweight and thermal insulation performance requirements of aluminum alloys,combined with the low density and thermal insulation performance advantages of hollow sphere structures,and prepared hollow sphere aluminum matrix composites by adding millimeter sized hollow spheres to the aluminum alloy matrix through powder metallurgy（PM）and vacuum hot-pressing sintering methods.To further improve the efficiency of hollow sphere forming and the mechanical and thermal insulation properties of aluminum matrix composites,a design concept and preparation method of metal-ceramic double shell hollow spheres（M-C HS）were proposed.By compounding high strength and low thermal conductivity 316L stainless steel（316L SS）metal shell on the exterior of Al₂O₃ceramic hollow sphere,a new type of 316L-Al₂O₃ metal-ceramic double shell hollow sphere was obtained,which improved the forming efficiency and corresponding mechanical properties of metal hollow spheres.This paper investigated on the"preparation process,microstructure and mechanical properties"relationship and forming mechanism of M-C HS through microstructure characterization and mechanical property testing,and optimized preparation process of M-C HS.Microstructure of the multi interface of multi shell hollow sphere structure in M-C HS/aluminum matrix composite was characterized.The interface damage and composite failure mechanism were studied through the characteristics of the compressive properties and microstructure change rules of the composite,and the preparation process of the composite was optimized.By analyzing the influence of M-C HS volume fraction on the compressive deformation behavior of composites,the mechanism of action and strengthening of M-C HS were studied.Thermal insulation properties and mechanism of M-C HS/aluminum matrix composites were tested and the thermal insulation mechanism of multi shell hollow sphere structure was investigated.An effective thermal conductivity prediction model suitable for multi shell hollow sphere structure composites has been established.The influence of sintering processes（sintering temperature,holding time）on microstructure of the metal shell in novel M-C HS and single M-C HS compressive property were emphatically studied,revealing the relationship between preparation process,microstructure and mechanical properties and forming mechanism of M-C HS.The increasing sintering temperature made the forming method of the metal shell in M-C HS changed from solid phase sintering to supersolidus liquid phase sintering（SLPS）.On the microstructure,a transition from sintering neck connection to rapid densification with the formation of liquid phase occurred.The analysis of single M-C HS compressive property and fracture surface showed that the deformation characteristics changed from brittle fracture to plastic deformation,and the failure mode changed from sintering neck fracture to hollow sphere compaction with increasing sintering temperature.The optimized M-C HS sintering process was sintered at 1200℃for 3h.Currently,the porosity of the metal shell of 316L-Al₂O₃ M-C HS is 0.14%,which is98.7%higher than that of 1100℃sintering temperature.The yield strength of the M-C HS is4.69MPa,which is 112.2%higher than that of 1100℃sintering temperature by solid-state sintering.M-C HSs prepared by the optimized preparation process were introduced into the aluminum matrix to prepare M-C HS/aluminum matrix composites with good metallurgical bonding interfaces by PM vacuum hot-pressing sintering method.The influence of sintering process on the interfacial microstructure,compressive properties and failure mechanisms of composites was studied.The Al₂O₃/316L interface was a mechanical bonding interface accompanied by element diffusion in composites.The 316L/Al interface was a metallurgical bonding interface formed by Fe-Al solid-solid interface reaction diffusion with Fe₄Al₁₃intermetallic compound（IMC）as the substrate ands-Cr flake phase and Mo rich lamellar phase precipitations.When the sintering temperature was 575℃,the holding time was 2h and the volume fraction of M-C HS was 20%,the composite exhibited the highest compressive strength（90.52 MPa）.Cracks propagated in multiple directions within a continuous IMC shell under load,limiting interfacial spalling.The optimized preparation process of the M-C HS/aluminum matrix composite was sintered at 575℃for 2 hours at a pressure of 5MPa.Based on exploring the microstructure of multi shell hollow sphere structure in M-C HS/aluminum matrix composites and optimization of composite preparation process,effects of M-C HS volume fraction and other factors on compressive properties of composites were studied.The deformation mechanism of M-C HS/aluminum matrix composites was revealed.When the volume fraction of M-C HS was lower than a certain content,M-C HS acted as a reinforcing phase.Deformation behavior of the aluminum matrix composites showed an increase in stress with increasing strain,with the maximum compressive strength appearing.When the volume fraction of M-C HS reached a critical volume fraction（≥40%）,the deformation behavior of aluminum matrix composites transformed into a characteristic of basically unchanged stress with increasing strain,exhibiting the typical platform characteristics and good energy absorption characteristics of porous materials.The"ceramic-metal-IMC"multi shell hollow sphere structure in M-C HS/aluminum matrix composites exhibited a"brittle-plastic-brittle"deformation characteristic during compression.The IMC and 316L SS metal shell were the main reasons for strength improvement of aluminum matrix composites.Thermal insulation performance,heat transfer law and insulation mechanism of M-C HS/aluminum matrix composites were studied using a combination of experiments,simulation,and theoretical calculations.Based on MAXWELL method,an effective thermal conductivity prediction model suitable for multi shell hollow sphere structure composites was established.With increasing volume fraction of M-C HS,the total heat flux in M-C HS/aluminum matrix composite decreased.The direction,path and transfer rate of heat flux in composites all changed.The heat conduction mode shifted from a single"bypass"M-C HS model to a combination of"bypass"and"pass through"models.When the volume fraction of M-C HS≥40%,the aluminum matrix composites achieved a decrease in effective thermal conductivity while maintaining compressive strength.When the volume fraction of M-C HS was 60%,the aluminum matrix composites exhibited the smallest thermal diffusivity and effective thermal conductivity,which were 20.88mm/s² and 29.51W/（m·℃）,respectively.The effective thermal conductivity prediction model established based on the above research provides a method for predicting the effective thermal conductivity and structural design of multi shell hollow sphere structured composites.When the volume fraction of M-C HS≥40%,the aluminum matrix composites achieved an improvement in thermal insulation property and energy absorption capacity while maintaining the same compressive strength as original aluminum matrix,providing a foundation for the mechanical and thermal insulation performance design of the composites.