Search Results (8)

The effects of partially substituting Al for Cu in Zr_59.62Cu_18.4-xNi₁₂Al_6+xNb₃Hf_0.78Y_0.2 (x = 0, 2, 4, 6, 8 at.%) bulk metallic glasses (BMGs) on their glass-forming ability (GFA), quasi-static and dynamic mechanical properties, and energy characteristics were investigated. The results showed that an appropriate substitution of Al for Cu can improve GFA and reach a critical casting size up to 10 mm. Additionally, with Al replacement of Cu, the change in the distribution and content of free volume inside the BMGs was the main reason for the quasi-static compression plasticity. In contrast, the BMGs exhibited no plasticity during dynamic compression and high-speed impact, owing to the short loading time and thermal softening effect. In terms of energy characteristics, all alloys have a high combustion enthalpy. And on the surface of the fragments collected from impact, the active elements Zr, Al, and Nb reacted because of the adiabatic temperature rise. Further, x = 4 at.% Zr-based BMG with its superior overall performance could penetrate a 6 mm Q235 plate at a speed of 1038 m/s, combining excellent mechanical properties and energy characteristics. This study contributes to the development of Zr-based BMGs as novel energetic structural materials. Full article

As an important strengthening phase in Al-Mg-Fe alloy, the elastic and ductile–brittle characteristics of Al₁₃Fe₄ intermetallics hold prime significance in ascertaining the mechanical properties and potential application of Al-Mg-Fe alloys. In this study, multialloying of Co, Cu, Cr, Mn, and Ni has been adopted for tuning the mechanical characteristics of the Al₁₃Fe₄ phase; their effects on mechanical features and electronic structure of the Al₁₃Fe₄ phase have been scrutinized systematically by first-principles calculations employing the density functional theory. The replacement of Fe with M (M = Co, Cu, Cr, Mn, and Ni) is energetically advantageous at 0 K, as evidenced by the negative cohesive energy and mixing enthalpy of all Al₁₃(Fe,M)₄ phases. Cu and Ni, on the contrary, have a detrimental impact on Al₁₃Fe_4′s modulus and hardness due to the evolution of chemical bonding strength. Co, Cr, and Mn are thus, interesting candidate elements. In the light of B/G and Poisson’s ratio (σ) criteria, Al₁₃Fe₄, Al₁₃(Fe,Cu)₄, and Al₁₃(Fe,Ni)₄ have superior ductility; however, Al₁₃(Fe,Co), Al₁₃(Fe,Mn), and Al₁₃(Fe,Cr)₄ tend to be brittle materials. Calculation-based findings show that Co, Cr, and Mn are appropriate alloying elements for enhancing fracture toughness, whereas Mn reduces Al₁₃Fe_4′s elastic anisotropy. The electronic structure assessment found that the mechanical properties of the intermetallics are predominantly influenced by the Al-M bonds when the alloying element M replaced Fe. Full article

Ni/Al energetic structural materials have attracted much attention due to their high energy release, but understanding their thermal reaction behavior and mechanism in order to guide their practical application is still a challenge. We reported a novel understanding of the thermal reaction behavior and mechanism of Ni/Al energetic structural materials in the inert atmosphere. The reaction kinetic model of Ni/Al energetic structural materials with Ni:Al molar ratios was obtained. The effect of the Ni:Al molar ratios on their thermal reactions was discussed based on the products of a Ni/Al thermal reaction. Moreover, depending on the melting point of Al, the thermal reaction stages were divided into two stages: the hard contact stage and soft contact stage. The liquid Al was adsorbed on the surface of Ni with high contact areas, leading in an aggravated thermal reaction of Ni/Al. Full article

In this study, SiCp/Al composites were bonded using the laser-induced exothermic bonding method. The nanostructured Al/Ni energetic materials were prepared by the high-energy ball-milling method and served as the bonding interlayer. The joint microstructure was characterized by SEM, EDS, TEM, and XRD. The effect of Zr content on the joint microstructure and shear strength was investigated. The results indicated that after the ball-milling process the Al and Ni particles underwent strong plastic deformations and were welded to each other, forming the nanostructured Al/Ni energetic materials with a lamellar structure. Compared with the raw powders, the location of the exothermic peak decreased by 42 K, and its exothermic performance was significantly improved. The exothermic reactions that occurred in the Al/Ni interlayer provided the required heat for the bonding process. Near the bonding interface, the interlayer could not react completely due to the cooling effect of the substrates, forming a mixture of residual metal particles and Ni-Al compounds. The addition of Zr content enhanced the interfacial reactions between the bonding interlayer and the SiCp/Al composites. The interlayer products transformed from NiAl to the eutectic organization of NiAl + Ni-Al-Zr, thus decreasing the pores in the joint and improving the bonding quality. With an increase in the Zr content, the joint shear strength first increased and then decreased. When the Zr content was 10 wt.%, the joint shear strength reached a maximum of 22 MPa. Full article

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-xW_x 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. Full article

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 Zr_68.5Cu₁₂Ni₁₂Al_7.5 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 Zr_68.5Cu₁₂Ni₁₂Al_7.5 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. Full article

Transition metal sulfide catalysts are actually the most performing catalytic materials in crude oil hydrotreating (HDT), for energetic purposes. However, these systems suffer from several drawbacks that limit their exploitation. Aiming to meet the even more stringent environmental requirement, through a remarkable improvement of HDT performance in the presence of refractory feedstock (i.e., in terms of activity, selectivity, and stability), a deeper knowledge of the structure–activity relationship of catalysts must be achieved. Therefore, in this study, CoMo/γ-Al₂O₃ and NiMo/γ-Al₂O₃ catalysts were characterized and tested in the o-xylene hydrogenation model reaction, assessing the influence of both support acidity and catalyst acid strength on reaction pathway by employing γ-Al₂O₃ and Y-Type zeolite as acid reference materials. A clear relationship between concentration and strength of acid sites and the performance of the catalytic materials was established. Cobalt based catalyst (CoMoS_x) proves a higher acidic character with respect to Nickel (NiMoS_x), prompting isomerization reactions preferentially, also reflecting a greater o-xylene conversion. The different chemical properties of metals also affect the catalytic pathway, leading on the CoMoS_x system to the preferential formation of p-xylene isomer with respect to m-xylene. Full article

Energetic structural materials (ESMs) have many potential military applications due to their unique functions. In this work, the reactivity and penetration performance of ESMs have been examined as a shaped charge liner material. The penetration experiments of nickel-aluminum (Ni-Al) and copper-nickel-aluminum (Cu-Ni-Al)-shaped charge liners (SCLs) have been designed and fired into 45# steel. The targets were recovered and analyzed by optical microscopy, electron microscopy, energy dispersive spectroscopy, and Vickers microhardness measurements. The head and tail of the crater walls penetrated by two reactive jets demonstrated unique microstructures. The jet rapidly decayed with the penetration process, but the “white” zone (a mixture of martensite and austenite) was more prominent in the tail, and the microhardness of the tail was much higher than that of the head. The results showed the continued exotherm of Ni-Al reactive jet when it was fired into the target. The addition of Cu reduced the exotherm of Ni-Al, Cu could not only increase the average crater size, but also raise the average penetration depth by 42%. These results offer valuable insight for utilizing ESM as shaped charge liner materials. Full article