Study On The Preparation And Mechanical Properties Of TiB₂ Reinforced 7050 Aluminum Matrix Functionally Gradient Materials

The rapid development of the aerospace field has provided a strong impetus for the continuous improvement of the performance of composite materials.Under extreme conditions,conventional homogeneous composites have been unable to meet the needs of some key components for higher performance.Therefore,functionally gradient materials are needed to relieve stress and protect these components.Among them,particle reinforced aluminum matrix composites have become one of the focuses of national aerospace new material research and development plans due to their lightweight advantages.The introduction of TiB₂ particles can improve the strength of7050 aluminum matrix composites,but may sacrifice their toughness.Therefore,it is necessary to achieve a balance between strength and toughness to comprehensively improve the mechanical properties of materials.In order to achieve this goal,its performance can be optimized by adjusting the distribution and content of different components in the composite.For example,forming a linear gradient structure or a soft-hard interleaved shell structure.It has great development potential to apply gradient configuration composite and bionic structure design to the study of strengthening and toughening of TiB₂/7050Al composites.The preparation process optimization,mechanical properties improvement and strengthening and toughening mechanism of TiB₂/7050Al composites were studied and discussed.The strengthening and toughening mechanism of the composite was revealed by studying the preparation process,microstructure and mechanical properties of the composite.The advantages of applying TiB₂/7050 Al functionally gradient materials to low-pressure compressor stator blades were verified by finite element simulation analysis.According to the actual application requirements,the study takes the innovative structure design,preparation of new materials,revealing the unique mechanism and verifying the application effect as the research ideas,which lays a certain foundation for the practical application of the composite material in the compressor and other aerospace fields.The key research accomplishments are summarized as follows:（1）The process parameters of TiB₂/7050Al composites during vacuum hot pressing sintering were optimized by orthogonal experimental design and multi-index matrix analysis.The results show that the effect of holding time on the overall performance of the composite is the most significant,the effect of sintering temperature is the second,and the effect of applied pressure is relatively small.After further optimizing the key factors-holding time and sintering temperature,it was found that the relative density,microhardness and tensile strength of the composite increased with the increase of holding time.With the increase of sintering temperature,these properties increase first and then decrease.Finally,the optimum sintering process parameters were determined as holding time of 120 min,sintering temperature of 590°C and applied pressure of 20 MPa.（2）Based on the linear gradient structure and the shell structure,a biomimetic-shell gradient structure composite material was designed.TiB₂/7050Al composites with homogeneous,linear gradient and biomimetic-shell gradient structure were successfully prepared by the optimal sintering process.The effects of TiB₂ content,gradient structure,load direction and soft layer material on the microstructure and mechanical properties were studied.The results show that the microstructure of each layer in the microstructure is uniform and the boundary between the layers is clear.In the range of 0-25 wt.%TiB₂,the bending strength of the three TiB₂/7050Al composites increased with the increase of TiB₂ content.Relatively speaking,TiB₂/7050Al functionally gradient materials show more significant advantages in terms of bending strength,especially when the load is applied on the higher TiB₂ content,and the TiB₂content in the soft layer and the hard layer is quite different,the maximum increase in bending strength reaches 20%.This is the result of the combined action of intra-layer strengthening between layers,inter-layer heterogeneous deformation induced strengthening,strain hardening,synergistic strengthening of strength layer and ductility layer,and inter-layer synergistic strengthening under strong constraints.This further highlights the advantages of the soft-hard interleaved and strong-tough complementary structure of the biomimetic-shell functionally gradient materials.（3）The effects of TiB₂ content,gradient structure,load direction and soft layer material on the fracture toughness and crack propagation behavior of TiB₂/7050Al composites were studied by in-situ observation.In general,increasing the content of TiB₂ will reduce the fracture toughness of TiB₂/7050Al composites.However,in the TiB₂/7050Al composites with a biomimetic-shell gradient structure,when the content of TiB₂ in the soft layer and the hard layer is significantly different,especially when the high content layer of TiB₂ is first subjected to load,the material exhibits excellent fracture toughness.This excellent fracture toughness benefits from the effective application of toughening mechanisms such as matrix plastic deformation,crack passivation,crack deflection,and crack branching.This effect effectively enhances the fracture toughness of TiB₂/7050Al functionally gradient materials,which is 22.50%higher than the theoretical average.Therefore,TiB₂/7050Al composites with biomimetic-shell gradient structure can be regarded as an ideal layered composite model.Because of its light weight,high strength and high toughness,it is suitable for engineering fields with high requirements for composite strength and toughness.（4）According to the performance parameters of TiB₂/7050Al composite obtained in the previous study,the application potential of the composite in actual parts is discussed.The finite element analysis results show that under the action of fluid,the flow velocity at the root of the blade reaches the maximum,and the blade is mainly affected by the bending stress.With the increase of TiB₂ content from 0 to 25 wt.%,the total deformation and equivalent stress of TiB₂/7050Al functionally gradient materials generally show a downward trend,indicating that the stress generated by high-strength composites under load is small.In addition,the stress level of TiB₂/7050Al linear functionally gradient materials is significantly reduced,and the maximum reduction is 14.51%.Relatively speaking,the effect of reducing the deformation of the biomimetic-shell functionally gradient materials is more significant,reaching 7.42%.