Preparation And Properties Of Multilayered Al/Ni Energetic Structural Materials With High Strength And Large Plasticity

Energetic structural materials（ESMs）with high mechanical properties and large exothermic energy are the multifunctional composites,which have been widely used in weapons,space debris protection,oil mining and so on.Under external stimuli（heating,current,laser,mechanical impact,etc）,ESMs can undergo chemical reactions and release a lot of energy.At present,most Al/Ni ESMs prepared by accumulative roll bonding and compression-sintering method contained many microstructural defects.As a result,Al/Ni ESMs were prone to premature fracture failure when subjected to external force loads,limiting their application in some structural parts.In order to obtain Al/Ni ESMs with high comprehensive properties（including density,strength,plasticity and energy density）,a facile approach of electrodeposition and hot pressing was proposed to prepare large-sized multilayered Al/Ni ESMs in this work,which achieved micron-scale Al/Ni layered structures of uniform and continuous distribution.Therefore,the technical problem of poor mechanical properties caused by internal defects could be solved fundamentally.The mechanical properties of multilayered Al/Ni ESMs under quasi-static and dynamic loading conditions were studied systematically.Besides,this work also emphasized the investigations of energy release characteristics of Al/Ni ESMs under external stimuli,such as heating,mechanical impact.The following main conclusions are drawn:（1）The effects of the thickness of Al/Ni bilayer,the hot pressing temperature,the hot pressing time and the thickness ratio of Al and Ni layer on the exothermic properties of multilayered Al/Ni ESMs were studied respectively.It was found that Al/Ni ESMs could quickly release more energy in a shorter time with the decrease of the bilayer thickness.The released heat of Al/Ni ESMs with the increase of hot pressing temperature or hot pressing time declined gradually due to the increase of diffusion layer thickness.When the hot pressing temperature rose from 250°C to 400°C with the hot pressing time of 0.5 h,the released heat decreased from 1076 J/g to 1003 J/g.And the released heat declined from 1003 J/g to 782 J/g as the hot pressing time increased from 0.5 h to 4 h at 400°C.An estimation model of the released heat was established,and the calculation results were in good agreement with the actual measurement results.The phase transition regularity during continuous heating showed that Al₃Ni phase was the preferentially generated phase.（2）The prepared multilayered Al/Ni ESMs appeared higher strength and better plasticity.As the hot pressing time increased from 0.5 h to 4 h at 400°C,the quasi-static tensile strength and quasi-static compression strength of multilayered Al/Ni ESMs both showed the trend of decreasing first and then increasing,but the elongation increased first and then decreased.This was due to the fact that when the hot pressing time exceeded 2 h,the newly formed hard and brittle Al₃Ni phases in Al/Ni interfaces had a serious cleavage effect on the matrix.Under hot pressing time of 4 h,the tensile strength and compressive strength of Al/Ni ESMs reached maximum values of 375.7 MPa and421.1 MPa,respectively.Al/Ni samples acquired the maximum elongation of 10.2%under hot pressing time of 1 h.When the thickness ratio of Al to Ni changed from 9:4 to 9:10,the bending strength and bending formability of multilayered Al/Ni ESMs were improved significantly.This was because the thicker Ni layer promoted the more continuous and uniform distribution,and the large percentage of Ni layer led to the increase of the strength and the improvement of the cooperative deformation of Al and Ni layers.（3）Quasi-static and dynamic compression experiments with different strain rate showed that the prepared multilayered Al/Ni ESMs exhibited high dynamic compression strength and excellent insensitive characteristics.When the compression strain rate increased from 10^-4 s^-1 to 5000 s^-1,the compression strength improved gradually for multilayered Al/Ni ESMs fabricated under hot pressing time of 1 h and 4 h,which appeared an obvious strain rate strengthening effect.When the compression strain rate reached 6500 s^-1,the thermal softening effect caused by the rapid increasing temperature under high strain rate led to severe reduction of dynamic compression strength for Al/Ni ESMs prepared at 1 h.However,the dynamic compression strength of Al/Ni ESMs with the hot pressing time of 4 h continually increased,since the effect of second phase strengthening induced by a large number of Al₃Ni particles crushed by the internal impact helped to offset the thermal softening effect.（4）The shock induced chemical reaction experiment showed that multilayered Al/Ni ESMs exhibited obvious impact released energy characteristics.It was proposed that a large number of uniformly distributed hot spots were sufficient consitions to maintain the self-propagating reaction.The reaction ratio of Al/Ni energetic fragments was calculated by collecting unreacted fragments,and an effective calculation method for the conversion rate of kinetic energy of energetic fragments into the system energy was proposed.With the increase of impact velocity,the overpressure peak and its duration in the hemispherical container were enhanced rapidly,and the reaction ratio and kinetic energy conversion rate of Al/Ni energetic fragments increased obviously.（5）The detonation reaction occurred when the fragments of multilayered Al/Ni ESMs impacted the double-plates target.Owing to the dual effects of kinetic energy and chemical energy,the Al/Ni fragments had a certain hole expansion effect on the main target.With the increase of impact speed of energetic fragments,the damage area of rear target increased evidently.The secondary deflagation reaction of energetic fragments resulted in conspicuous damage effects such as bulge,crack,perforation and flanging tear to the rear target.