| Ti/Al3Ti metallic laminated composite is a new kind of composite which is composed by alternately paving the Ti layer and intermetallic Al3Ti layer.Such a material have properties of low density,high strength,high modulus and high energy absorption,which enables it to be potentially applied in the area of military armor protection.At present,the main fabrication method of Ti/Al3Ti metal laminated composites is hot sintering,and the obtained structure of this metallic laminated composite is mainly the flat sheet,which significantly constrains its engineering applications.Driven by the current existing problems of the manufacture and application of Ti/Al3Ti metallic laminated composites,a new process of manufacturing curved structured metallic laminated composite of Ti/Al3Ti high strength and high toughness was proposed,which basically follows the routine of ultrasonic consolidation,hot forming and in-situ reaction process.Through the methodology of combining theoretical analysis,experimental research and numerical simulation,the key technologies and corresponding mechanisms of this novel process have been systematically investigated.Ti/Al composite sheets were made using the ultrasonic consolidation technique.The results have shown that,the bonding strength of Ti/Al interface firstly increases and then decreases with the increase of ultrasonic pressure.It also increases monotonically with increasing the amplitude.Under the condition of ultrasonic pressure of 2.0 kN and amplitude of 35 ?m,the optimal ultrasonic consolidated interface was obtained with a peering strength of 58.08 N/cm.During the ultrasonic consolidation process,a severe plastic deformation occurs at the Ti/Al interface,which results in the grain refinement phenomenon.Metallurgical boding was obtained for part of the Ti/Al interface,while the rest showed a mechanical joining.Ti element was found within the matrix of aluminium grains at the Ti/Al interface,which proves that diffusion of the Ti element into Al foils occurs during the ultrasonic consolidation process.The in-situ reaction experiment and numerical simulation were used to investigation the process of Ti/Al in-situ reaction.The results have shown that,different reacted products and defects were generated in the in-situ reacted layer of Ti/Al composite sheets.When the reaction temperature was relatively low,the reaction product was only Al3Ti,and tunnel-shaped or delamination cracks were formed in Al3Ti layer,which was dependent on the reaction time.When the reaction temperature was relatively high,the reaction products would include Al3Ti,Al2Ti,AlTi and AlTi3,and void defects would be induced in the reaction layer.The residual stress with alternatively distributed f tension-compression state existed in the Ti/Al3Ti laminated composites,where the Ti layer sustained compressive residual stress,while tensile residual stress for the Al3Ti layer.With the increasing of the number of layer,the maximum compressive stress of the Ti layer increases,while the maximum tensile stress of Al3Ti layer decreases.Appropriate number of Al layers is able to change the distribution of residual stress in the composite,e.g.Al3Ti layer would sustains compressive stress as well as the Ti layer,and such a compressive stress increases with increasing the Al layer thickness.The altered residual stress sate enables to effectively inhibit the generation of tunnel-shaped cracks during the in-situ reaction process.The mechanical properties of Ti/Al3Ti layered composites were studied using cold compression,Hopkinson compression bar and ballistic tests.The results have shown that,the obtained mechanical properties of Ti/Al3Ti laminated composites were determined by the process conditions of in-situ sintering reaction.Using semi-solid sintering reaction,better mechanical properties can be obtained compared those using solid-state sintering reaction and liquid sintering reaction.The maximum values of mechanical properties of Ti/Al3Ti laminated composites were obtained under the sintering condition of 660?/3 h,where the quasi-static compressive strength reached 1432 MPa,and the dynamic compressive strength reached 1735 MPa at a strain rate of 2860 s-1.The ballistic limit V50 of Ti/Al3Ti laminated composite was about 509 m/s,which was equivalent to the protection ability of Q235 steel,while its density was only 41%of Q235 steel.After the penetration of billet,only a crater formed without fragmentation can be observed,which indicates that the composite has the ability to resist multiple projectiles.During the failure of Ti/Al3Ti laminated composite target sheet,the failure mode of Ti layer was mainly divided into two parts:local tensile and shear failure at the front Ti layer in the target plate,and petal tensile failure of Ti layer at back of target plate,respectively.The failure mode of Al3Ti layer was fracture caused by the sustained stress waves.The deformation behavior of Ti/Al composite sheets was studied by tensile tests.The fabrication method of layered composite curved surface structure was explored using the bending forming and in-situ reaction tests.Ti/Al composite sheet is both temperature and rate sensitive.With of the increase of temperature,the peak stress of composite decreases and the elongation increases;With the increase of strain rate,both the peak stress and elongation of the composite increases.Under the condition of 550? and 0.003 s-1,the optimal formability of Ti/Al composite was obtained with a peak stress of laminated Ti/Al composite sheet was 343.4 MPa.The bending formability of Ti/Al composite sheet was related to forming temperature,forming pressure and holding time.With the increase of forming temperature,pressure and holding time,both the height of formed part and geometry accuracy increases significantly.Under the condition of 550? forming temperature,20t forming load and 1min holding time,the percentage of springback of Ti/Al laminated sheet after forming was 15%approximately,and the ratio of blank attached on the die reaches-5 mm of the bent Ti/Al laminated composite.A curved surface structure of Ti/Al3Ti laminated composite was manufactured by bending forming and in-situ reaction.The uniform thickness distribution and chemical composition,and the defect-free dense A13Ti layer successfully prove the feasibility of the proposed technical routine. |
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