Study On Multiple Forging Process And Heat Treatment Of TiBw/Ti-6Al-4V Composites Materials

Discontinuously reinforced titanium matrix composites(DRTMCs)are attractive structural parts in potential applications of aerospace industries owing to their high specific strength,high-temperature durability and corrosion resistance properties.However,the DRTMCs with a homogeneous reinforced structure prepared by PM generally exhibit poor plastici ty at ambient temperature,which severely restricts the development and application of PM techniques.Fortunately,mechanical properties of DRTMCs,especially ductility,can be improved significantly by tailoring reinforcement in the form of inhomogeneous distributions.Another possible alleviation is that the mechanical properties can be improved by adjusting the distribution of prefer red orientation of TiB whisker.Therefore,it is necessary to systematically study the influence of inhomogeneous distribution of reinforcements on mechanical properties of TiBw/Ti-6Al-4V composites.Consequently,isothermal multi-direction forging will be adopted to design and prepare titanium matrix composites with different reinforcements distributions.Besides,the difference of matrix microstructures is then narrowed and eliminated by cyclic heat treatment.So,the main subject of the present study is to figure out the influence of the different kinds of reinforced structures on mechanical property of the prepared composites.In this paper,titanium matrix composites with various spatial structures of TiB reinforcements such as oblateness and ellipsoids were prepared by forging;the evolution of the microstructure of composite materials in the preparation process was explored;the properties of titanium matrix composites with different thermoplastic processing techniques were compared.The study found that multi-directional forging could not only flexibly regulate the reinforcement of the spatial structure,but also greatly improve the matrix microstructure and weaken the texture.With the increase of cumulative deformation,the TiB space-enhanced structure presented different structures such as spheres,oblateness,ellipsoids,fibers under different forging processes.The microstructure of the matrix gradually transformed from a large number of elongated original α grains to fine and eqyuiaxed α grains.All the forged billets had excellent comprehensive mechanical properties: elongation over 5%,twice of that of extruded billets,and higher tensile strength over 1250 MPa compared to the as-sintered billet.In addition,cyclic heat treatment and second intermediate heat treatment were utilized to study the influence of cyclic heat treatment on the evolution of microstructure and mechanical properties to testify the ability of cyclic heat treatment to unify different matrix microstructure to control virable.The study found that the aspect ratio of the strip α decreased,and there was a clear tendency to spheroidize with the increase of the number of cycles.After 7 cycles,the aspect ratio of the strip α tended to be uniform and after 9 cycles,the equiaxed structure could be seen clearly.After cyclic heat treatment,uniform sepherical α grain and β grain in which tiny lamellar α grains were distributed.The morphologies in cross section and longitudinal section were similar,which proved the cyclic teat treatment’s capability to unify the matrix microstructure.Subsequently,on the basis of heat treatment,the shear lag model was used to quantitatively characterize the effect of different spatial structures on the mechanical properties of reinforcements in this paper in order to provide reference for future research and development of non-uniform reinforced titanium matrix composites and engineering applications(especially forgings).