Study On Microstructure,mechanical And Anti-penetration Performance Of Ti/Al₃Ti And Ti/Al₃Ti/Al Heterostructures

High strengthening and toughening,lightweight metal materials are considered to be the most promising research direction in the next decade,which are capable of satisfactory performance under extreme environments.In particular,Ti/Al intermetallics with low density,high specific strength and specific modulus are regarded to have significant prospects in aerospace,military equipment and other fields.Among them,Al₃Ti has the lowest density（3.36g/cm³）and the largest Young’s modulus（216 Gpa）,which is a potential lightweight material in structural design.However,their processability and engineering application were restricted at ambient temperature due to the intrinsic brittleness.A large number of research results show that the heterogeneous structure（HS）can achieve a synergistic improvement of material strength and plasticity by combining and matching the mechanical properties of individuals.Thus,providing a new pathway to the research and application of Al₃Ti.However,due to the effects of interface constraints,layered composition,grain size and mechanical properties,the mechanical responses,failure modes and strength-toughening mechanisms of HS are more complicated.During the whole deformation process,local defects of materials often dominate,and even lead to the premature fracture of materials.The inhibition of crack initiation and propagation are considerable to improve the toughness of materials.Therefore,the distribution and evolution of local strain during tensile deformation need to be studied in detail via the microstructure characterization of heterostructures.Based on these,Ti/Al₃Ti and Ti/Al₃Ti/Al heterostructures were prepared by vacuum hot-pressing process in this study.The microstructure,local strain and crack propagation behavior were characterized by EBSD,digital image correlation（DIC）and in-situ tensile.The deformation behaviors,failure modes and external toughening mechanisms of heterostructures were analyzed during room temperature compression and tensile tests.And the improvement of residual Al on tensile ductility for Ti/Al₃Ti/Al heterostructures was revealed.On the basis,the numerical simulation of anti-penetration performance of Ti/Al₃Ti/Al laminated target was carried out using Ls-Dyna.The failure process of individuals based on the stress wave theory and the stress distribution of individuals was studied,and the target optimization work was carried out.The relevant research contents and conclusions are as follows:（1）.With the increase of hot-pressing temperature,the Ti grains in TC4 layer are significantly refined by continuous dynamic recrystallization mechanism,which leads to the migration of grain boundaries,the proliferation of intragranular dislocations,and the increased dislocation density under the higher hot-pressing deformation.As is shown in KAM maps,the misorientation is found to significantly increase,and its migration and distribution behavior are found to change from the grain boundaries and heterogeneous interface to the heterogeneous interface and within grains.In addition,the grain size of Al₃Ti layer increases and the grains are found to grow,while the dislocation density changes a little.Actually,the microstructures of Ti/Al₃Ti interfaces and Al₃Ti/Al interfaces are significantly different,which is related to the diffusion process and the degree of dynamic recrystallization near the different interfaces.（2）.Through the analysis of tensile test and DIC,the elongation of Ti/Al₃Ti/Al heterostructure is 64.2～228.5%higher than that of Ti/Al₃Ti heterostructure,which is attributed to the uniform and stable plastic flow of Ti/Al₃Ti/Al heterostructure,and the regulating effect of residual Al on its deformation and fracture behavior.The improvement mechanisms of residual Al on tensile plasticity were found that normal strain was delocalized by promoting strain flow,and shear strain was stabilized by hindering effects.In addition,the failure mechanism of heterostructures,from HS650 to HS600,is found to transform from brittle fracture determined by normal strain into ductile shearing fracture governed by normal strain and shearing strain,respectively.The above conclusions show that the ambient-temperature ductility can be significantly improved by regulating the local strain distribution of the heterostructure during tensile deformation.（3）.The failure process of each individuals in Ti/Al₃Ti and Ti/Al₃Ti/Al heterostructures is different from that in homogeneous state.The fracture micromorphology revealed that a mixed model of transgranular and intergranular was presented in the Al₃Ti layers.Dimples with different morphologies are distributed in TC4 layers,which belongs to voids coalescence failure.A large number of tearing ridges are overspread in Al layers,which is attributed to the severe plastic deformation and a number of effective slip systems during the tensile process.（4）.Ti/Al₃Ti heterostructures without obvious Kirkendall voids and centerlines can be prepared by endothermic semi-solid method.In-situ tensile tests reveal that the external toughening mechanisms of Ti/Al₃Ti heterostructures include crack deflection,crack blunting,ligament bridging,multiple crack propagation modes and plastic deformation of ductile Ti layer.The inhibition of Ti layer on crack tip propagation can significantly improve the toughness of Ti/Al₃Ti heterostructures.（5）.The deformation process in the anti-penetration process includes local penetration hole and global deformation.The failure process includes the fragmentation of Al₃Ti layer induced by compression wave,interface delamination failure induced by tensile longitudinal wave,and the tensile failure couples shear failure induced by tensile shear wave and shear wave in ductile layer.Among them,the Al layer has wave-absorpted characteristics and energy absorption;the TC4 layer has an external toughening effect on Al₃Ti and energy absorption,and the thickness of the Al₃Ti layer determines the residual velocity of the projectile and acquiring a supporting effect on the adjacent layer.The design idea of maximizing the areal-density energy absorption of Ti/Al₃Ti/Al laminated target is that requiring a thicker TC4 layer,and matching reasonable thickness of Al₃Ti layers and Al layers to synergistically improve the energy absorption characteristics of the Ti/Al₃Ti/Al laminated target.