Research On The Mechanical Anisotropy Of 4.2wt.%TiB₂/2024Al Rolling Plates Used In Aeroengine

Nacelle is one of the core components of aircraft power unit.Due to late starting and patent blockade,the nacelle manufacture industry in China is still a blank field.As a new generation of structural materials,Al matrix composites has the characteristics of light weight,high strength and great resistance to fatigue which is suitable material for nacelle manufacturing.The anisotropy would introduce defects during curve plate forming process and the crack propagation is the key factor for fatigue failure since the material is subjected to cyclic load during its service life.Therefore,it is of great interest to study the anisotropic behavior as well as to explore the behavior of crack growth mode in anisotropy.In this article,the in-plane anisotropy of yield strength,the evolution of their microstructure and the crack propagation for 4.2wt.%TiB₂/2024Al plates were analyzed with the help of tensile tests(including uniaxial tensile test and notch tensile test)and microscopic analysis approaches(including polarized optical microscope,POM;scanning electron microscope,SEM;transmission electron microscope,TEM;neutron diffraction analysis and electron back-scattered diffraction analysis,EBSD).Several conclusions were drawn as follows:The yield strength of rolled state 4.2wt.%TiB₂/2024Al plate has in-plane anisotropy.After the specimen having gone through T4 treatment,its yield strength exhibits excellent isotropy.The anisotropy emerges again for specimen having gone a pre-stretching process after T4 treatment.The larger the pre-stretching amount is,the more obvious the anisotropy is.Introduction of large amount of dislocation during severe plastic deformation by TiB₂ particles provides driving force for recrystallization.The static recrystallization induced during natural aging,which leads to the texture randomization,is the cause of excellent isotropy of yield strength for T4 treated specimens.The difference in the difficulty of slip activation under various loading direction,which is caused by pre-stretching process,is the reason of its anisotropy.An innovative method was put forward by combining the slip transmission analysis,three-dimensional crack deflection model and the EBSD analysis around the crack to quantitatively analyze the effects of grain boundaries in inhibiting the crack propagation.It was found that the twist angle at grain boundaries plays an important role.