Study On Preparation And Properties Of Ni-Al Metallic Energetic Material

The Ni-Al Metallic Energetic Material(MEM), a mixture of Ni and Al elemental powders, has a certain mechanical properties and density, which could undergo a violent chemical reaction and release great amounts of thermochemical energy under strong impact loadings. It is considered the best candidate material for air defense missile warheads. In this thesis, we focus on how to improve the mechanical properties of Ni-Al MEM with no or less reducing in the energy density.The energy density and mechanical properties of Ni-Al Metallic Energetic Materials were studied by exploring the different composition ratios, using different preparation methods. The effects of sintering temperature, powder particle size and preparation method on the interface diffusion, mechanical properties, initial reaction temperature and energy density of MEMs were investigated by X-ray diffraction(XRD), universal testing machine and differential scanning calorimeter(DSC) methods. Meanwhile, the behaviors of impact energy release were investigated under different impact velocities by ?14.5mm ballistic gun with a quasi-sealed impulse response systems and a high-speed video system.The Ni-Al(molar ratio is 1:1) MEMs were prepared by cold-pressing and sintering with elemental powders or Ni-coated Al powder. The effect of sintering temperature on the mechanical properties and energy density(Ed)of Ni-Al metal energetic materials was investigated. The results demonstrate that the increasing sintering temperatures results in the decrease in energy density and increase in mechanical properties.at the sintering temperature rangeing from 510 ? to 550 ? with elemental powders as starting materrials. In present invesitgations, the Ni-Al MEM with excellent combination of energy density and mechanical properties can be obtained by sintering Ni-Al green body at 550?, of which the tensile strength, compressive strength and energy density are 66.0MPa, 294.6MPa and 436.1J/g, respectively. The Ni-Al MEM undergoes a violent chemical reaction and releases a great amount of thermochemical energy under testing impact loadings. The increasing impact velocity results in the increase in energy release efficiency and degree of reaction, beyond the initiation threshold velocity of 974 m/s. As for using Ni-coated Al powder as starting material, the range of effective sintering temperature was 460 ? to 510 ?, obviously lower than that of Ni-Al MEM from elemental powders. The Ni-Al MEMs from Ni-coated Al pwoder present higher energy densityes, lower tensile and compressive strengths in comparison with Ni-Al MEM from elemental powders.As for the Ni-Al(Ni-Al molar ratio 9:11) MEM prepared by cold spray and sintering route, the tensile and compressive strengths increase initially and then decrease with the increasing sintering temperatures. The Ni-Al MEM with excellent combination of energy density and mechanical properties can be obtained by sintering cold-sprayed Ni-Al green body at 460?, of which the tensile strength, compressive strength and the energy density are 81.0MPa, 291.0MPa and 553.1J/g, respectively.In summary, the Ni-Al MEMs with excellent combination of energy density and mechanical properties can be obtained by both cold spray-sintering and cold pressing-sintering to meet the basic requirements in storage, transportation, launch and other conditions.