Study On Rapidly Solidified Nano TiB₂/Al Composite Powder And Its Composites

As more stringent demands,such as specific strength and specific stiffness,have been put forward along with the rapidly developing aviation and aerospace fields,the conventional metal material can't meet those demands already.Particle reinforced aluminum matrix composite can enhance material strength and wearing resistance,while the integration of ceramic particles often severely degrades the plasticity and machinability of the matrix as they're in micrometer-sized range.The ductility and toughness of in-situ aluminium composites can be maintained or even improved with a simultaneous increase in strength by reducing the particle size to the nanometer range.The composites also have a well machinability.However,the nanoparticles tend to agglomerate along the grain boundaries.To homogeneously distribute nanoparticles in the metal matrix is still a challenging task.Here we show that a uniform distribution of a high fraction of TiB₂nanoparticles in Al-based metal matrix powders with fine grain structure is achieved by gas atomization solidification processing.Taken atomized TiB₂reinforced composite powders as raw materials,uniformly distributed nano-ceramic particles reinforced composite can be fabricated after sintering and hot extrusion.The resulting Al-based composite exhibits better performance in mechanical properties.This thesis researched the microstructure of the rapidly solidified TiB₂reinforced aluminium composite powders,studied the influence factors of grain size of the powders,investigated the orientation relationship between TiB₂ particles and?-Al and studied the influence of the orientation relationships on the distribution of TiB₂ particles inside grains.This thesis also observed the microstructure of the TiB₂ reinforced bulk composite and analyzed the high toughness behavior of aluminium composite.The research of the composite powders shows that the powders exhibit fine equiaxed grain structure.TiB₂ nanoparticles improve grain refinement.The change of alloy composition has little effect on the solidification behavior of the composite powders.Particle size will affect the distribution of TiB₂:big particles distributing along grain boundaries while small particles being engulfed within the grain.The majority of TiB₂ particles inside grains and few particles along grain boundaries form well-documented crystallographic orientation relationship with Al.The formation of the crystallographic orientation relationship will improve particle engulfment during solidification,thus resulting a relatively uniform distribution of TiB₂ particles.After sintering and hot extrusion,TiB₂ reinforced Al-Cu-Mg bulk composite can be obtained.The study on the bulk composite shows that TiB₂reinforced Al-Cu-Mg composite have a fine grain structure and the average grain size don't change greatly even after heat treatment.TiB₂ distribute uniformly inside the metal matrix.Compared with the metal matrix material,our composite shows a higher tensile strength and ductility.