Preparation And Dynamic Properties Of TC4/Al₃Ti Laminated Composites

With the development of science and technology,the civilian fields?vehicle and high-speed train industries?,aviation,aerospace and military fields requires the materials to possess higher performance.This not only requires the material to have higher strength,but also requires the material to have lower density.Therefore,lightweight,as well as mechanical properties,has become one of the most important issues in material field.TC4/Al₃Ti laminated composite becomes a class of potential lightweight,high-strength protective material because of its low density,high specific modulus,high specific strength,high toughness and excellent impact resistance.The effects of vacuum degree,heating mode,pressing mode and heat treatment after fabrication with respect to the quality of TC4/Al₃Ti laminated composites were discussed in detail.The results show that the vacuum environment can significantly accelerate the reaction time and improve the production efficiency,and can increase the density of the prepared materials obviously.Compared with the surrounding heating method,the plate heating method can effectively reduce the initial brittle crack density of TC4/Al₃Ti laminated composites.Compared to the traditional hydraulic system pressurization method,the electric cylinder pressure can be more accurate,more sensitive,more timely to adjust the indenter displacement and load.Then the volume fraction of TC4 layer in TC4/Al₃Ti laminated composites can be precisely controlled and the density of the prepared samples can be improved.Hot isostatic pressing heat treatment can effectively improve the density and elastic modulus of TC4/Al₃Ti laminated composites.At the same time,the hot isostatic pressing heat treatment will slightly reduce the compressive strength of TC4/Al₃Ti laminated composites,and the plastic deformation ability of TC4/Al₃Ti laminated composites is obviously increased.In order to understand the complicated microstructure and interface features,XRD,SEM EDS and EBSD techniques are employed to characterize TC4/Al₃Ti MIL composites.The result shows that the only reaction product is intermetallic Al₃Ti when the hot pressing sintering reaction temperature is in range of 650-670?.The alloying element Cu can enhance the hardness of Al₃Ti in this area.Most of Al₃Ti grains in the reaction layer are equiaxed grains and have no preferred orientation.Near the TC4/Al₃Ti interface,more than80%of the Al₃Ti layer has a grain size of no more than 4?m.There is a significant stress concentration at the interface of TC4/Al3Ti,making the interface fracture easily in tensile,three-point bending and impact tests.Under the tensile stress,the quasi-static and dynamic tensile strengths of TC4/Al3Ti interface are 51.1 MPa and 79.3 MPa,respectively,and the lower tensile strength is one of the most important reasons for the prior fracture of TC4/Al3Ti interface.Under the bending stress,TC4/Al3Ti laminated composites also fracture from TC4/Al3Ti interface.For better understanding the damage evolution under impact condition,low-speed impact tests of TC4/Al3Ti laminated composites with different bullet types and different speeds were studied using Hopkinson rod launcher.The results show that delamination was the main failure mode in TC4/Al3Ti laminated composites,which was caused by the tensile stress wave.The TC4/Al3Ti laminated composites are damaged only in the surface unit at the lower impact velocity.At higher impact velocity,the whole specimen is bent and delaminated.The failure form of TC4/Al3Ti laminated composites is between the flat-ended bullet and the conical-ended bullet.The impact penetration and anti-penetration performance and damage evolution of TC4/Al3Ti laminated composites in medium-speed impact were studied using12.7 mm armor-piercing incendiary bomb.The results show that the average penetration ratio of TC4/Al₃Ti laminated composites is 108.6 J/kg?m^-2,and the mass protection coefficient is 1.56.The damage of TC4/Al3Ti laminated composites under high-speed impact is studied using two-stage light aerosol cannon.The results show that the damage in the back of TC4/Al3Ti laminated composites is obviously larger than that of the sample in the front.It is shown that under high-speed shock,the compressive strength of the specimen results in a large amount of compressive crack in the specimen and interlaminar cracking caused by the reflection of the tensile wave.In addition,the density effect exacerbates the shear failure effect of the specimen under high impact.