Energetic Structural Materials Research Articles

High-strength and energetic Al2Ti6Zr2Nb3Ta3 high entropy alloy containing a cuboidal BCC/B2 coherent microstructure

The present work developed a novel high-strength and energetic Al 2 Ti 6 Zr 2 Nb 3 Ta 3 high entropy alloy (HEA) containing a BCC/B2 coherent microstructure. The microstructural evolution of BCC/B2 with both the aging temperature (873 ~ 1073 K) and aging time (up to 200 h) was investigated, from which it was found that the cuboidal BCC nanoparticles are coherently-precipitated into the B2 matrix in 873 K-aged state due to a moderate lattice misfit ( ε ~ - 0.76%). The increase of aging temperature could destroy the BCC/B2 coherency and accelerate the formation of brittle Zr 5 Al 3 phase. Especially, the BCC/B2 microstructure exhibits an excellent thermal stability, as evidenced by the fact that these cuboidal BCC nanoprecipitates were not coarsened obviously at 873 K with the particle size from r ~ 10 nm in 24 h-aged state to r ~ 20 nm in 200 h-aged state. This alloy possesses prominent mechanical properties with high yield strength at both room temperature ( σ YS = 1193 MPa) and elevated temperatures (1060 MPa at 873 K and 106 MPa at 1273 K), where the high strength was discussed in light of the precipitation strengthening mechanism. Importantly, the current alloy has an ultrahigh combustion calorific capacity with a value of 10240 J·g -1 , showing a great potential to be used as novel high-performance energetic structural materials. • A high-strength and energetic HEA was developed with the cluster formula approach. • High-strength of alloy was realized by forming a BCC/B2 coherent microstructure. • The BCC/B2 coherent microstructure exhibits a higher thermal stability at 873 K. • The alloy has an ultrahigh combustion calorific value of 10240 J·g -1 .

Characterization of Ta-Ni-Al energetic structural material fabricated by explosive consolidation

Multi-element intermetallic energetic structural materials (ESMs) can be applied as reactive fragment, reactive shell and reactive shaped charge. As typical of intermetallics ESMs, Ni-Al ESMs have been heavily studied. However, the low density limits its application. This work proposed to improve the performance of Ni-Al ESMs by adding Ta. The nearly fully dense Ta-Ni-Al ESMs with a molar ratio 4:3:3 was successfully fabricated by explosive consolidation. The density was high up to 10.52 g/cm3 (98.3% theoretical maximum density). The heat treatment was used to further improve the performance of the Ta-Ni-Al ESMs. The microstructure characteristics were analyzed by scanning electron microscopy, X-ray diffraction and transmission electron microscope. The mechanical properties, reaction and impact-induced energy release have been systematically studied. Firstly, quasi-static and dynamic compression tests were conducted to analyze the mechanical properties of the sample before and after heat treatment. Secondly, the reaction characteristics in different atmospheres were discussed by differential scanning calorimetry and thermogravimetric analysis. The effect of the additive Ta was concerned. Furthermore, Impact-induced energy release tests on the Ta-Ni-Al ESMs were performed to understand the energy release properties. Based on these tests, the characterization of Ta-Ni-Al ESMs fabricated by explosive consolidation was obtained. There was no intermetallic formed in explosive consolidated samples. After the heat treatment, Ta-Ni-Al ESMs have good plasticity and strain rate effect. Meanwhile, under high impact velocity, the impact-induced energy release capability of Ta-Ni-Al ESMs was equivalent to Ni-Al ESMs.

Effects of microstructure on mechanical and energy release properties of Ni–Al energetic structural materials

Ni–Al energetic structural materials (ESMs) has been widely applied in defense field, because of its good mechanical and energy release properties. The effects of the microstructure on mechanical and energy release properties of ESMs are not well understood. In this study, by designing the particle size Ni:Al = 1 μm:25 μm and Ni:Al = 20 μm:25 μm, two kinds of samples, Ni continuous phase (Nicp) and Al continuous phase (Alcp), were prepared by explosive consolidation. The microstructure characteristics were analyzed by scanning electron microscopy, electron backscatter diffraction, and transmission electron microscope. Quasi-static and dynamic compression tests were also conducted to analyze the mechanical properties. It showed that the Nicp ESMs had higher quasi-static compressive strength of 325 MPa and fracture strain of 21.3%, compared with the Alcp ESMs having the strength 275 MPa and the fracture strain 17.5%. Also, the dynamic compressive strength of the Nicp ESMs sample is higher than that of the Alcp ESMs sample. The reaction characteristics of the two ESMs in different atmospheres were discussed by differential scanning calorimetry. The result showed that the reaction temperature of the Nicp ESMs was lower. Impact-induced energy release tests on the two ESMs were performed to understand their energy release properties. The results showed that the microstructure had significant effects on the ignition velocity threshold and reaction efficiency. The Nicp ESMs has better reaction performance because of the high interface density.

Tungsten combustion in impact initiated W–Al composite based on W(Al) super-saturated solid solution

Element W can effectively improve the density of energetic structural materials. However, W is an inert element and does not combust in air. To change the reaction characteristics of W, 60 at.% Al was introduced into W through mechanical alloying. XRD analysis shows that after 50 h of ball milling, the diffraction peak of Al completely disappears and W(Al60) super-saturated solid solution powder is obtained. Further observation by HAADF and HRTEM reveals that the W(Al60) super-saturated solid solution powder is a mixture of solid solution and amorphous phase. Based on the good thermal stability of W(Al60) alloy powder below 1000 °C, W(Al60)–Al composite was synthesized by hot pressing process. Impact initiation experiments suggest that the W(Al60)–Al composite has excellent reaction characteristics, and multiple types of tungsten oxides are detected in the reaction products, showing that the modified W is combustible in air. Due to the combustion of tungsten, the energy release rate of the W(Al60)–Al composite at speed of 1362 m/s reaches 2.71 kJ/g.

A Novel Understanding on the Thermal Reaction Behavior and Mechanism of Ni/Al Energetic Structural Materials

A Novel Understanding on the Thermal Reaction Behavior and Mechanism of Ni/Al Energetic Structural Materials

Characterization of Ta-Ni-Al Energetic Structural Material Fabricated by Explosive Consolidation

Characterization of Ta-Ni-Al Energetic Structural Material Fabricated by Explosive Consolidation

Effect of Ti on the Structure and Mechanical Properties of TixZr2.5-xTa Alloys.

To determine the effects of Ti and mixing entropy (ΔSmix) on the structure and mechanical proper-ties of Zr-Ta alloys and then find a new potential energetic structural material with good me-chanical properties and more reactive elements, TixZr2.5−xTa (x = 0, 0.5, 1.0, 1.5, 2.0) alloys were investigated. The XRD experimental results showed that the phase transformation of TixZr2.5−xTa nonequal-ratio ternary alloys depended not on the value of ΔSmix, but on the amount of Ti atoms. With the addition of Ti, the content of the HCP phase decreased gradually. SEM analyses revealed that dendrite morphology and component segregation increasingly developed and then weakened gradually. When x increases to 2.0, TixZr2.5−xTa with the best mechanical properties can be ob-tained. The yield strength, compressive strength and fracture strain of Ti2.0Zr0.5Ta reached 883 MPa, 1568 MPa and 34.58%, respectively. The dependence of the phase transformation and me-chanical properties confirms that improving the properties of Zr-Ta alloys by doping Ti is feasible.

Compression properties and impact energy release characteristics of TiZrNbV high-entropy alloy

To explore the potential of high-entropy alloys (HEAs) as energetic structural materials (ESMs), the compression behaviors and impact energy release characteristics of TiZrNbV HEA were investigated. Mechanical experiments at strain rates from 1 × 10−3 s−1 to 1 × 104 s−1 showed that TiZrNbV HEA exhibits clear dynamic brittle fracture behavior under dynamic compression loading, which is diametrically opposite to its behavior under quasi-static compression loading. A Johnson–Cook constitutive model for TiZrNbV HEA was obtained by fitting the experimental data, which demonstrated an apparent strain rate effect. Numerical simulation and microstructure results revealed the role of an adiabatic shear band (ASB) in the brittle fracture. The crack profiles that evolved from the ASB exhibited the typical characteristic for high temperatures. The degree and rate of the chemical reaction and recycled products of direct ballistic tests indicated that severe oxidation reactions induced by the high-temperature profiles resulted in chemical energy release under impact loading. The relationship between the material microstructure and macromechanical behavior of TiZrNbV HEA, which is important in the use of HEAs as ESMs, was revealed in this study through mechanical and material methods and finite element numerical simulation.

Effect of W on the Impact-Induced Energy Release Behavior of Al–Ni Energetic Structural Materials

Energetic structural materials (ESMs) are an important class of military materials due to their good structural and energy-releasing characteristics. To improve the damage effect of metal–metal ESMs with good mechanical properties, W was added to the 48Al–52Ni composites, and the effect of W on the impact-induced energy release behaviors was investigated. The results showed that the hot-press process and the addition of W did not change the microstructure and surface state of the constituent particles, leading to a stable onset temperature of the Al–Ni intermetallic reaction in (48Al–52Ni)100-xWx composites. Meanwhile, the decrease in the contact area between Al and Ni in the composites with increased W content resulted in the decrease in reaction heat. During the impact process, the intermetallic reaction of W caused by the Al–Ni intermetallic reaction, as well as the oxidation reaction of Al and Ni caused by the brittle fracture along the weak interface, caused the released energy of (48Al–52Ni)40W60 to reach 2.04 kJ/g.

Combustion/decomposition characteristics of 3D-printed Al/CuO, Al/Fe2O3, Al/Bi2O3 and Al/PTFE hollow filaments

In recent decades, the preparation of various metastable intermolecular composites (MICs) has been widely reported in pursuit of excellent reactivity and safety. However, there is still relatively little research on structural energetic materials (EMs) through 3D printing of MICs inks. In this work, the hollow filaments with different MICs formulas were prepared by 3D printing using a core-shell nozzle. The morphology, thermal decomposition and gas-generation performance of the filaments were characterized, and the different combustion stages of the filaments were analyzed. The results show that the hollow filaments exhibit shorter unsteady combustion time and significantly increased steady flame propagation rate compared with solid filaments. For the hollow filaments of Al/CuO/F2311 formula (15 wt % of F2311), the unsteady combustion time is as low as 0.65 ms, and the steady flame propagation rate reaches 206.936 g/s. Thermal analysis and constant-volume combustion tests show that Al/CuO/F2311 formula provides the lowest thermal decomposition onset temperature (288 °C) and the best gas-generation performance (peak pressure: 0.191 MPa, pressurization rate: 12.337 MPa/s) compared with other composites.

Study on the Impact-Induced Energy Release Characteristics of Zr68.5Cu12Ni12Al7.5 Amorphous Alloy.

As a new kind of multifunctional energetic structural material (MESM), amorphous alloy will undergo a chemical reaction and release energy under impact load. In this paper, an analysis method for the impact-induced reaction parameters of solid materials was derived based on a three-term equation of state and Avrami–Erofeev equation. The relation between the degree of reaction, pressure, and temperature of Zr68.5Cu12Ni12Al7.5 amorphous alloy was obtained. The influence of participation of an oxidizing reaction on the material energy release efficiency was analyzed. The relation between the energy release efficiency and impact velocity was achieved by an experiment in which Zr68.5Cu12Ni12Al7.5 amorphous alloy fragments impact a steel plate. The variations of pressure and temperature during the impact process were obtained. In the end, a reaction kinetic model was modified, and the kinetic parameters for the impact-induced reaction of materials in an air environment were obtained.

Structural Energetic Properties of Al/PVDF Composite Materials Prepared Using Fused Filament Fabrication

AbstractThe constituents of an aluminum/polyvinylidene fluoride multifunctional energetic structural material (MESM) were varied in order to determine the effect of solids loading and particle size on the structural energetic properties of the material. More specifically, seven different material formulations were paired with additive manufacturing to quantify key performance metrics relevant to the MESM use case. Determined via the quasi‐static tensile testing of 3D printed dogbone samples, both the modulus of elasticity and the ultimate strength was found to be heavily dependent on the solids loading; respectively increasing from 71 MPa to 208 MPa and decreasing from 34.5 MPa to 21.6 MPa, when transitioning from a 10 % Al loading to a 50 % Al loading. To characterize the combustion properties, a thermochemical code was used to predict the heat of combustion and the adiabatic flame temperature for the formulations considered, showing a maximum predicted temperature near 20 % Al. Also, burning rate measurements were conducted on the 3D printed formulations in order to quantify their combustion performance. When burning in air, a maximum burning rate was found to occur at the slightly fuel‐rich condition of 30 % Al. Upon completion of the characterization, the trade‐off between mechanical performance and combustion performance was visualized by plotting critical MESM design parameters against one another.

Energy Release Characteristics of Ni–Al–CuO Ternary Energetic Structural Material Processed by Cold Spraying

Ternary energetic structural material (ESM) Ni–Al–CuO was prepared by cold spraying, and its mechanical properties studied under quasi-static-state and dynamic compression conditions. Energy release characteristics including the ignition temperature, energy release, and combustion wave velocity were characterized in both the thermal explosion and self-propagating combustion modes. The results reveal that the yield stress of Ni–Al–CuO is 50 MPa higher than that of Ni–Al. The initial reaction temperature was found to be 450 °C, much lower than the temperature of the reaction between Al and CuO and corresponding to the reaction of Ni and Al. In addition, more energy was released by Ni–Al–CuO ESM (859.2 J/g) than by Ni–Al (735.4 J/g). The combustion wave velocity of the Ni–Al–CuO coating was about 90 mm/s. Self-propagating combustion of Ni–Al–CuO proceeded via a multistage reaction, during which the Al–CuO reaction was triggered by the Ni–Al reaction.

The Effect of Process Parameters on the Structural Energetic Properties of Additively Manufactured Reactive Structures

Abstract This paper investigates the ability of an aluminum-fluoropolymer energetic material to act as a multifunctional energetic structural material (MESM). The mechanical properties of the material were determined by performing quasi-static tensile testing of 3D printed dogbones. Samples were prepared with and without particle loading, as well as with different print directions, in order to gain a fundamental understanding of how these parameters affect the mechanical properties of the material. Larger truss samples were printed in order to simulate realistic structural elements. Samples were printed in different directions and burned to determine this parameter’s effect on the combustion performance of the material. The aluminum polyvinylidene fluoride mixtures considered were shown to have viable structural capabilities as well as sufficient combustion performance. The structural energetic capabilities of the formulations considered, paired with the material’s ability to be 3D printed, could enable a number of interesting applications in the aerospace and defense industry.

Fabrication and characterization of the Ni–Al energetic structural material with high energy density and mechanical properties

Abstract The fully dense Ni–Al energetic structural material (ESM) was successfully fabricated by using shock consolidation, with no reaction between the constituents. The microstructure, quasi-static and dynamic compressive behavior and energetic characteristics were investigated. The results revealed a uniform microstructure along the cross-section and both phases were continuously distributed. No intermetallic was detected by the XRD and a 5 nm thick interlayer composed of amorphous phase and crystalline phase was observed at the Ni–Al interface by TEM. The interfacial strength was shown to have a strong effect on the ductility and the strength of Ni–Al ESM, and could be significantly improved by solid-state diffusion during the shock loading and the following heat-treatment. After heat-treatment the samples showed a high quasi-static compressive strength of 300 MPa and a ductility of 14.5%. At impact velocity above 671 m/s, the Ni–Al ESM was initiated and released a large amount of rising the shock temperature or energy. Its reaction efficiency strongly depends on the impact velocity. The good mechanical properties and energetic characteristics of the Ni–Al ESM shows a great potential for the shock consolidation in fabrication of metallic energetic structural materials.

Preparation and properties of w(Al) alloy powders

In order to improve the density and penetrating ability of Al/Ni energetic structural materials, W with the high density and hardness generally was introduced. But the oxidation reaction of W factually is difficult to induce because of the strong binding energy. It then results in the great reduce of energy release. In this work, W(Al) super-saturated solid solution powders with the average particle size of 3.9μm, were synthesized by mechanical alloying. In this super-saturated solid solution, Al atoms are evenly distributed in the W lattice and Al content can reach 80 at.%. Moreover, Al is still stable in the lattice of W but not form Al-W intermetallic, when W(Al) powders were annealed at 1200°C for 30 min in vacuum. As a large amount of Al atoms into W, the activity of W is greatly improved, thus the combustion heat of W(Al) super-saturated solid solution powders can reach about 11.3KJ/g.

Effect of in-situ crystalline phases on the mechanical properties and energy release behaviors of Zr55Ni5Al10Cu30 bulk metallic glasses

To explore the application potential of bulk metallic glasses (BMGs) as energetic structural materials (ESMs) and 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 BMGs are evaluated. The results indicate that while the content of in-situ crystalline phases in Zr55Ni5Al10Cu30 alloy are effectively tailored by controlling the cooling rate of molten alloys, the mechanical properties and energy release behaviors of Zr55Ni5Al10Cu30 are determined by the content of in-situ crystalline phases. The alloy prepared using the highest cooling rate possesses the lowest crystalline phase content as well as the highest strength and deformability. By contrast, the complete crystalline alloy prepared by annealing exhibits the highest energy release characteristics under high-speed impact owing to the highest degree of brittleness and most oxidation reaction. The Zr55Ni5Al10Cu30 alloy with different crystalline phase content shows potential as an ESM. Its mechanical properties and energetic characteristics can be effectively tailored by controlling the content of in-situ crystalline phases via cooling rate modulation.

Microstructure Evolution and Compressive Properties of Multilayered Al/Ni Energetic Structural Materials under Different Strain Rates

Multilayered Al/Ni energetic structural materials integrating exothermic properties and mechanical properties were prepared by the method of electrodeposition and hot pressing in this research. Then, the uniaxial quasi-static compression and split Hopkinson pressure bar experiments were conducted at strain rates from 10−4 to 6.5 × 103 s−1 at room temperature. The effects of compression strain rate on the microstructure evolution and the compressive properties of multilayered Al/Ni energetic structural materials were systematically investigated. With increasing quasi-static compression strain rate, the compression strength increased slightly for two kinds of Al/Ni multilayers prepared under different hot pressing time. With the hot pressing process extending to 4 h, the dynamic compression strength of multilayered Al/Ni composites monotonically increased from 494.7 to 564.2 MPa with increasing strain rate. It was shown that Al/Ni energetic structural materials exhibited evident strain hardening and strain rate strengthening. However, when the compression strain rate reached 6500 s−1, the Al/Ni composite prepared with the hot pressing time of 1 h showed prominent thermal softening. Notwithstanding, it was found that the compression strength of Al/Ni composite prepared at 4 h was evidently higher than that at 1 h, since the second phase reinforcement counteracted the thermal softening. In addition, the critical failure strain presented obviously increasing tendency with the increased compression strain rates.

Multilayered Al/Ni energetic structural materials with high energy density and mechanical properties prepared by a facile approach of electrodeposition and hot pressing

With an aim to fabricate multilayered Al/Ni energetic structural materials integrating high energy density and mechanical properties, a facile approach of electrodeposition and hot pressing was employed in this study. The effect of hot pressing time on exothermic reactions and mechanical properties has been systematically investigated. It was found that the exothermic heat of Al/Ni energetic structural materials decreased from 1003J/g to 782J/g, while the hot pressing process increased from 0.5 h to 4 h, and the initial exothermic reaction temperature declined simultaneously. Because of the increasing crystallite sizes of Ni and Al layers at hot pressing time of 1 h, Al/Ni multilayered materials acquired the maximum elongation, the minimum tensile strength and the lowest compressive strength. As the hot pressing process exceeded 2 h, the elongation deteriorated sharply and the compressive strength aggrandized significantly owing to the formation of the hard brittle Al3Ni phases in Al/Ni interfaces.

The shock-induced chemical reaction behaviour of Al/Ni composites by cold rolling and powder compaction

Al/Ni composites are typical structural energetic materials, which have dual functions of structural and energetic characteristics. In order to investigate the influence of manufacturing methods on shock-induced chemical reaction (SICR) behaviour of Al/Ni composites, Al/Ni multi-layered composites with 3–5 cold-rolling passes and Al/Ni powder composites were obtained. Microstructural observation using scanning electron microscopy (SEM) and two-step impact initiation experiments were performed on the four Al/Ni composites. Furthermore, mesoscale simulations, through importing SEM images into the finite element analysis to reflect the real microstructures of the composites, were performed to analyse the particle deformation and temperature rise under shock compression conditions. The experimental results showed the distinct differences on the SICR characteristics among the four Al/Ni composites (i.e. by 3, 4 and 5 cold-rolling passes and powder compaction). The manufacturing methods provided the control of the particle sizes, particle distribution and the content of the interfacial intermetallics at scale of different microstructures, which ultimately affected the temperature distribution, as well as the contact between Al and Ni in Al/Ni composites under shock loading. As a result, the Al/Ni powder composites showed the highest energy release capacity among the four composites, while the energy release capability of Al/Ni multi-layered composites decreased with the growth of rolling passes.