Design Preparation And Ballistic Mechanism Of Layered Gradient B₄C_p/Al Composites

The development of high mobility and strong defense of combat weapons in the battlefield puts forward higher requirements for armored materials.Functionally graded materials has become one of the important development trends of future armor materials due to it's excellent characteristics.In order to solve the problems of high-quality preparation of FGMs,the absence of constitutive model of particles reinforced metal matrix composites and the unclear ballistic mechanism of FGMs,a gradient B₄C_p/2024Al composites with ceramic content ranging from 25 to 70 vol.%was designed and fabricated.The influence of B₄C content on the microstructure and static and dynamic mechanical properties of B₄C_p/2024Al was systematically studied.A constitutive model suitable for describing the dynamic behavior of aluminum matrix composite was proposed.The ballistic performance of B₄C_p/2024Al gradient composites were tested.The ballistic mechanism was analyzed based on macro and micro damage of materials and one-dimensional stress wave calculation.The gradient material is designed based on stress wave calculation.70-47-25vol.%B₄C/2024Al gradient composites were prepared by liquid metal infiltration process and powder gradation.B₄C particles distribute uniformly in each gradient layer,and the Al matrix is continuous between gradient layers.There are no obvious defects in B₄C/2024Al gradient composites.The microstructure of each gradient layer under T6 heat treatment was observed.Al₃B₄₈C₂ and Al₃BC are found at the interface of Al and B₄C.Mg and O element segregate at the interface of Al-B₄C,which changes the type and morphology of precipitates.The precipitated phase in25vol.%B₄C/2024Al composites is mainly s'phase which is coherent with Al.The precipitated phases in 47vol.%B₄C/2024Al composites are s'and?'phase.The precipitated phase in 70vol.%B₄C/2024Al composites is mainly?phase.The quasi-static properties of B₄C_p/2024Al with different B₄C content were tested.The elastic modulus and hardness of B₄C_p/2024Al increased with the increase of B₄C content.The bending strength and quasi-static compressive strength show a trend of first increasing and then decreasing with the increase of B₄C volume fraction.The plasticity decreases with the increase of B₄C content.The dynamic compressive true stress-true strain curves at different temperatures and strain rates show obvious strain softening phenomenon.The softening mechanism is mainly the decrease of effective bearing capacity caused by the breakage of B₄C reinforcements,and also includes the dynamic recovery,dynamic recrystallization,and adiabatic temperature rise.The classical Johnson-cook model is modified by introducing a strain softening term(1?^k).The prediction results of the modified Johnson-cook model for the flow stress of B₄C/2024Al composites are more consistent with the experimental results than the classical Johnson-cook model.The ballistic performance of thin and semi-infinite 70-47-25vol.%B₄C/2024Al gradient composites targets were tested by 7.62mm API.The results show 70-47-25vol.%B₄C/2024Al gradient composites have a better anti-penetration performance than homogeneous 47vol.%B₄C/2024Al.The protection coefficient and thickness coefficient of the semi-infinite target can reach 3.18 and 1.06respectively.The microstructure observation of 70-47-25vol.%gradient B₄C/2024Al composites semi-infinite target after penetration shows that different gradient layer shows different damage morphology.A large number of broken B₄C particles are observed in 70 vol.%B₄C/2024Al composites in the top layer.And B₄C particles contain stacking faults,twins and dislocation walls.The damages of 47vol.%B₄C/2024Al in the middle layer include microcoids,crack deflection and a small amount of broken B₄C particles.The damages of 25vol.%B₄C/2024Al composite are microcoids,microcracks and dynamic recovery of Al matrix.Different damages of composites at each gradient layer indicate that each gradient layer plays a different role during the penetration.For 70vol.%B₄C/2024Al composites in the top layer,particle fragmentation and projectile abrasion are the main energy dissipation mechanism.For 47vol.%B₄C/2024Al composites in the middle layer,plastic deformation of composites and abrasion on projectile are the main energy dissipation mechanism.Apart from that,47vol.%B₄C/2024Al composites can reduce target damage by crack deflection and reducing reflected tensile stress wave strength.25vol.%B₄C/2024Al composites in the bottom layer absorb the residual energy through plastic deformation.The ballistic mechanism of 70-47-25vol%gradient B₄C/Al composites is that the reflected tensile stress wave intensity is reduced duo to gradient structure with continuous matrix.And the formation of ceramic smash cone is effectively restrained in the top layer with high B₄C content.