Research On Prepartion,mechanical And Thermal Characteristics Of Metallic Energetic Structural Materials

To enhance the damage effects of ammunition,energetic structural materials(ESMs),which can realize the integration of structural and energetic by replacing the traditional inert metals,were developed.Among recent ESMs,Al-based composites and Zr-based bulk metallic glasses(BMGs)display a relatively good mechanical properties and energy densities.However,Al-based ESMs,such as Al-Ni,exhibit the low effect of energy release.In addition,the applications of Zr-based ESMs are restricted by the problem in fabricating large size BMGs.To improve energy release performance of Al-Ni composites,and explore the application of Zr-based BMGs,the effects of additives and in-situ crystalline phases on the mechanical properties,oxidation and impact-induced reactions are investigated.The differential scanning calorimetry(DSC)results of Al-Ni composite showed that when the mass percentage of Al was 48%,the reaction heat of Al-Ni composite reached the maximum,?1.30 k J·g^-1,and the reaction onset temperature was?760 K.Under the impact with the speed of 1400m·s^-1,partially intermetallic formation reaction along with oxidation of metals took place,leading to a releasing energy of 2.28k J·g^-1.When 2–15 wt.%CuO were added into Al-Ni(48 wt.%Al)composite,CuO particles clustered in the continuous Al matrix.Tensile strenghth of the composites with2?15 wt.%CuO were 193–216 MPa,close to that of Al-Ni composites.The DSC,heat treatment,and ballistic tests results of(48Al-52Ni)100-x(CuO)x indicated that Al and Ni were more prone to donate their free electrons after the addition of CuO.A decrease in the number of free electrons as well as weak metal-oxygen bonds at the Al/Ni interfaces caused by thermal decomposition of CuO,impeded the activity of the Al-Ni intermetallic formation reaction,increasing its onset temperature from 766 K to 820 K in DSC tests.The reduced difference in onset temperatures for the intermetallic formation and thermite reactions caused the thermite reaction between Al and CuO to be ignited by the Al-Ni intermetallic formation reaction.The overlap of these two exothermic reactions greatly improved reaction intensity(from 7.5 m W·mg^-1 to 45?80m W·mg^-1),and then accelerated the oxidation of Al and Ni,finally enhancing energy release performance during high-speed impact(from 2.28 k J·g^-1 to 3.31–3.86 k J·g^-1).When 2–15 wt.%MoO₃ were added into Al-Ni(48 wt.%Al)composite,MoO₃attached on the Al particles as a monolayer structure and broke the continuity of the Al matrix.The presence of brittle MoO₃ at the Al/MoO₃ interfaces leaded to the occurrence of intergranular fracture and the decrease in the toughness of(48Al-52Ni)100-x(MoO₃)x under a quasi-static loading.Meanwhile,the increase in the Al/MoO₃ interfaces resulted in the more charge transfer between MoO₃ and Al,then leading to a higher onset temperature of Al-Ni intermetallic formation(830-850 K)and a stronger heat flow caused by the co-contribution of intermetallic formation and thermite reactions(70-80m W·mg^-1).The lower toughness and the higher reaction heat flow jointly make the releasing energy of the composites with 6–10 wt.%MoO₃ reach?4.20 k J·g^-1,under the impact with the speed of 1400m·s^-1,which is larger than that of the(48Al-52Ni)100-x(CuO)x composites.When 60 wt.%W were added into Al-Ni(48 wt.%Al)composite,tensile strength and intermetallic formation reaction behavior did not change obviously,while the mass density increased from 4.18 g·cm^-3 to 7.44 g·cm^-3 as well as the ductility decreased from3.18%to 1.7%.The increase in the brittleness of W-added Al-Ni composites resulted in the increase in the oxidation reaction of Al,then leading to the releasing energy of(48Al-52Ni)40W60 composite reach 2.43 k J·g^-1,which was 3 times for that of the Al-Ni(48 wt.%Al)composite,under the impact with the speed of 1200 m·s^-1.To address the limitations in the preparation of large-sized monolithic BMGs,the effect of the in-situ crystalline phases on the mechanical properties and energy release behaviors of Zr55Ni5Al10Cu30(at.%)BMGs are evaluated.The results indicated that the content of in-situ crystalline phases in Zr55Ni5Al10Cu30 alloy are effectively tailored by controlling the cooling rate of molten alloys.The alloy prepared using the highest cooling rate possesses the lowest crystalline phase content(?6 vol.%)as well as the highest strength(1443 MPa)and ductility(1.5%).By contrast,the complete crystalline alloy prepared by annealing exhibits the highest energy release characteristics under high-speed impact(?3.14 k J·g^-1),owing to the highest degree of brittleness(fracture strain?0.8%)and most oxidation reaction.The mechanical properties and energetic characteristics Zr55Ni5Al10Cu30 BMGs can be effectively tailored by controlling the content of in-situ crystalline phases via cooling rate modulation.