Transition between interface defeat and penetration for tungsten projectiles and four silicon carbide materials

Armour systems containing high-quality ceramics may be capable of defeating armour-piercing projectiles on the surfaces of these hard materials. This capability, named interface defeat, has been studied for four different silicon carbide ceramic materials, viz., SiC–B, SiC–N, SiC–SC–1RN and SiC–HPN by use of a light-gas gun and a small-scale reverse impact technique. The velocities of a tungsten projectile marking the transition between interface defeat and penetration have been determined and compared with the Vickers hardness and fracture toughness of the ceramic materials. It is found that the transition velocity increases with the fracture toughness but not with the Vickers hardness. This indicates that, under the prevailing conditions, fracture may have had more influence than plastic flow on the transition. As a consequence, the observed transition velocities may not be the maximum ones achievable, at least not for SiC–B, SiC–N and SiC–SC–1RN. By suppression of the initiation and propagation of cracks through increase of the confining pressure, it may be possible to increase the transition velocities.     

Penetration dynamics and interface defeat capability of silicon carbide against long Rod impact

To determine the behavior of silicon carbide (SiC) against long rod impact a detailed study with experiments in the velocity range from 0.8 to 3 km/s at normal impact conditions was performed in recent years. Interest ranged from penetration performance of intact and pre-damaged SiC to interface defeat capability of SiC. Together with impact data in the hypervelocity regime this paper provides a comprehensive overview of the penetration dynamics of SiC over a wide velocity range and during different phases of the penetration process.     

Formation process of mixed silicon and tungsten carbide from copyrolysis of polysilane and metallic tungsten: Part I

Copyrolysis of polysilane with metallic tungsten addition in the range of 0–12 at % W was performed. A significant decrease of the mass loss during the polysilane pyrolysis was observed. Also the specific surface area, gas evolution and occuring phase formation changed. The tungsten forms silicides and carbides depending on the applied pyrolysis temperature. The reactions are controlled by transport phenomena of carbon and tungsten. In the end of the process the silicon carbide (SiC) and tungsten carbide (WC) are stable. The obtained powders are sintered to porous ceramics with a significant pore gradient and a variation of the hardness in a micrometer range.     

Influence of interface compounds on interface bonding characteristics of aluminium and silicon carbide

The interface plays an important role in improving the mechanical properties of metal matrix composites. Hence, it is essential to evaluate interface bonding of Aluminium/Silicon carbide. The interface bonding of Aluminum/Silicon carbide samples were prepared by various processing temperatures at constant holding time. The interface compounds at the interface were evaluated by an energy dispersive spectroscope and diffusion length of compounds was calculated by Arrhenius equation. The interface structure was analyzed by a scanning electron microscope. The interface characteristics were evaluated by tensile test and microhardness test.     

基于A-T模型的长杆弹超高速侵彻陶瓷靶体强度分析

Alekseevskii-Tate(A-T)模型广泛应用于长杆弹超高速冲击的终点效应分析中。A-T模型对于金属弹靶强度有明确的表达式,而对于陶瓷靶体强度尤其是弹体初始冲击速度大于1 500 m/s时还没有统一的结论。基于长杆钨弹超高速(1 500~5 000 m/s)侵彻三种陶瓷(Al N,B4C,Si C)/铝复合靶体的缩比逆弹道实验数据;基于A-T模型,给出了上述陶瓷材料在不同侵彻速度范围内的靶体强度表达式。进一步通过与47发长杆钨弹超高速(1 250~2 500 m/s)侵彻陶瓷(Al N,B4C,Si C,AD85)/RHA钢复合靶体DOP实验数据对比,验证了提出的陶瓷靶体强度表达式的适用性。     

Influence of scale on the penetration of tungsten rods into steel-backed alumina targets

As ballistic tests are often performed in reduced geometrical scale, the scaling laws are important for the interpretation of the results. In this study, we tested the validity of replica scaling, by which we mean that all geometrical dimensions are scaled uniformly, while the materials and the impact velocity are kept the same. Long tungsten projectiles with length-to-diameter ratio 15 were fired against unconfined alumina targets with steel backing. The tests were carried out with impact velocities 1500 m s⁻¹ and 2500 m s⁻¹, and in three different scales with projectile lengths 30, 75 and 150 mm (diameters 2, 5 and 10 mm). The alumina targets were photographed by means of a high-speed camera, and the tungsten projectiles were photographed inside the alumina targets by means of flash radiography. Also, the residual penetrations in the steel backings were measured. The Johnson-Holmquist model for ceramic materials was implemented into the AUTODYN code, which was used for simulation of the experiments. The agreement between results of experiment and simulation was fair, and over the tested interval of scales replica scaling was found to be valid with reasonable accuracy.     

主控因素对异型头弹丸半侵彻金属靶深度的影响特性研究

为研究异型头弹丸半侵彻金属靶的侵深特性,基于量纲方法对影响侵深的主控因素进行了分析,采用弹道枪加载和LS-DYNA软件对异型头弹丸半侵彻金属靶的作用过程进行了试验和数值模拟研究,分析了异型头弹丸结构、弹丸初速、靶板厚度等因素对侵彻深度的影响规律,获得了侵深随弹丸初速以及靶板厚度的变化曲线。研究结果表明,弹丸初速和靶板厚度是影响侵彻深度的关键因素,并拟合得到了弹丸初速和靶板厚度综合影响下的半侵彻侵深经验公式。研究结果可为半侵彻作用的研究及新型侵彻的工程计算方法等提供参考。     

The transition from 2D to 3D nanoclusters of silicon carbide on silicon

We have evaluated the critical average distance between the nanoclusters of silicon carbide grown by molecular beam epitaxy on silicon and estimated the time of the transition from two-to three-dimensional growth.     

Normal impact of blunt projectiles on moving targets: experimental study

An experimental investigation was performed to study impact on targets moving at right angles to the striker trajectory with a velocity of 40 m/s. Tests were executed with a compressed gas gun using 6.35 mm diameter, 38.1 mm long hard steel blunt-nosed cylindrical strikers in the velcity range 49–213 m/s and with a powder gun using a blunt 9.53 mm diameter cylindrical projectile with an aspect ratio of 2 up to velocities of 492 m/s. The post-impact projectile trajectory and attitute as well as the configuration of the craters produced in thin targets of cold-rolled steel and soft aluminum were observed. The impact process produced asymmetric plugging followed by either front or side petaling. The latter phenomenon was found to be controlled by the ultimate tensile strain of the target and the ratio of the projectile to target speed. The test parameters and resulting data were primarily selected to permit comparison with the predictions of an analytical model of the process described in a companion paper.     

Normal impact of blunt projectiles on moving targets: Analytical considerations

An analytical model for the normal impact of blunt, cylindrical and undeformable projectiles on thin metallic targets moving in a plane normal to the initial bullet trajectory has been developed. This analysis is intended to depict the principal phenomena that occur when such a projectile strikes the center of a circular plate mounted at the end of an arm rotating about the other end at constant angular velocity. The first step in the simulation constructions of the construction of a three-stage plugging process involving plastic wave propagation, joint projectile/target motion and tensile failure designed for impact on a stationary plate, using a membrane theory for the target response. This axisymmetric representation was then applied to moving targets by employment of impulse-momentum laws. Petaling failure was portrayed by an upper-bound plasticity approach, while projectile motion was described by rigid-body dynamics. The principal assumption inherent in this representation were guided by geometric considerations and observations from tests described in a companion paper.

Model evaluation was performed for several cases of projectile and target speed combinations. Relevant solutions were compared with results from corresponding experiments. In general, good correlation were obtained; discrepancies could be attributed to the effect of features that had not been incorporated in the model.     

聚碳硅烷先驱体转化法制备SiC涂层研究

以自合成的聚二甲基硅烷(PDMS)为原料,常压裂解合成聚碳硅烷(PCS),通过FT-IR分析PCS的结构,用GPC测定其分子量及分布,用熔点分析仪测定其熔点.在此基础上,采用聚碳硅烷先驱体转化法在石墨基体上制备SiC涂层,通过X射线衍射对涂层进行晶相分析,用扫描电镜分析涂层表面和横断面的形貌.结果表明,在石墨基体上形成了明显的β-SiC晶相,可以获得均匀、致密的SiC涂层,其厚度可通过涂层次数的改变进行调节,单次涂层最大厚度大约为2μm.     

The influence of confinement on the penetration of ceramic targets by KE projectiles at 1.8 and 2.6 km/s

This paper presents the results of scale size experiments using a tungsten-alloy long-rod projectile fired against 97.5% Al₂O₃ ceramic targets at 1.8 and 2.6 km/s. Two targets were used, one having lateral steel confinement; the other without. The projectile overmatched the target, and residual projectile length and velocity were recorded using ballistic-syncro photography. Flash radiography was used during penetration of the unconfined target to obtain the penetration velocity. Manganin pressure gauges were also used to obtain additional data on the response of the ceramic target during penetration. Results from the eight experiments indicate that the confinement reduced the residual energy of the projectile at both impact velocities. Expressed in terms of the projectile impact energy, 55–56% was lost in the unconfined target at 2.6 km/s compared with 60% for the confined design. The same trend was found at 1.8 km/s with 68% and 72–73% for the unconfined and confined, respectively. Predictions using the QinetiQ GRIM2D hydrocode and a simplified form of the Johnson–Holmquist ceramic material model agreed well with the experiments for three out of the four test configurations. The predicted projectile erosion and retardation against the confined target at 1.8 km/s was excessively high. Analytical predictions using the Tate modified Bernoulli equation also gave reasonably accurate predictions for three of the tests, but values for the Tate target ‘strength’ extracted from experiments using a different target configuration were not accurate for the target design used in this paper.     

Structural changes in tungsten wire and their effect on the properties of hydrogenated nanocrystalline cubic silicon carbide thin films

We investigated the structural changes in tungsten wire heated to 1800 °C in SiH₄/CH₄/H₂/N₂ atmosphere and the effect of the aging tungsten wire on the properties of N-doped hydrogenated nanocrystalline cubic silicon carbide (nc-3C-SiC:H) thin films. The aged tungsten wire had two parts: hot parts of the middle of the wire and relatively cold parts connected to clamps. Tungsten carbide (W₂C) layer formed in the wire of the hot parts, while crystalline silicon and cubic silicon carbide (c-Si/3C-SiC) layer deposited on the wire of the cold parts. N-doped nc-3C-SiC:H thin films were deposited for 5 min (thickness: ~ 30 nm) after the tungsten wire was heated under the same condition as during the film deposition for given times (exposure time). No changes in the structural, electrical and optical properties of the nc-3C-SiC:H thin films were observed for the exposure time up to 450 min.     

Chloride vapor-phase epitaxy of gallium nitride on silicon: Effect of a silicon carbide interlayer

A new approach is described, according to which the use of a thin silicon carbide (SiC) interlayer ensures the suppression of cracking and the simultaneous release of elastic strain in gallium nitride (GaN) epilayers grown by hydride-chloride vapor-phase epitaxy (HVPE) on 1.5-inch Si(111) substrates. Using this method, 20-μm-thick GaN epilayers have been grown by HVPE on Si substrates with AlN (300 nm) and SiC (100 nm) interlayers. A high quality of the obtained GaN epilayers is confirmed by the photoluminescence spectra, where an exciton band with hv_max = 3.45 eV and a half-width (FWHM) of 68 meV is observed at 77 K, as well as by the X-ray rocking curves exhibiting GaN(0002) reflections with a half-width of ω_? = 600 arc sec.     

Aluminum nitride on silicon: Role of silicon carbide interlayer and chloride vapor-phase epitaxy technology

A new approach to the deposition of aluminum nitride (AlN) layers with thicknesses ranging within ∼0.1–10 μm on silicon single crystal substrates by hydride-chloride vapor-phase epitaxy (HVPE) has been developed and implemented, which involves the formation of thin (∼100-nm-thick) intermediate silicon carbide (3C-SiC) interlayers. It is established that wavy convex bands with a height of about 40 nm are present on the surface of as-grown AlN layers, which are situated at the boundaries of blocks in the layer structure. It is suggested that the formation of these wavy structures is related to morphological instability that develops due to accelerated growth of AlN at the block boundaries. Experiments show that, at low deposition rates, AlN layers grow according to a layer (quasi-two-dimensional) mechanism, which allows AlN layers characterized by half-widths (FWHM) of the X-ray rocking curves of (0002) reflections about ω_θ = 2100 arc sec to be obtained.     

The wettability of silicon carbide by liquid aluminium: the effect of free silicon in the carbide and of magnesium,silicon and copper alloy additions to the aluminium

Results from the sessile-drop method are reported for the effects on wetting angle, , of free silicon in the silicon carbide substrate and of alloy additions of silicon, copper or magnesium to the aluminium drop for the temperature range 700–960 or 1040 °C in a titanium-gettered vacuum (10^–4/10^–5 torr; 1 torr=133.322 Pa). Wetting angle, , was reduced by a factor as large as 2.8 for pure aluminium on reaction-bonded, compared with sintered silicon carbide, attributable to partial dissolution by the aluminium of the 18 wt% free silicon present in the reaction-bonded material. For wetting of reaction-bonded silicon carbide, the addition of 5 wt% silicon, copper or magnesium to the aluminium gave contact angles that decreased in the sequence SiCuMg, with the magnesium addition being the only one to result in wetting (i.e. <90 °) for all conditions studied. These results may have implications for design of conditions for joining or promotion of infiltration of silicon carbide parts, preforms or arrays with aluminium alloy melts.     

Oxidation resistance of hafnium diboride—silicon carbide from 1400 to 2000?°C

Oxidation resistance tests were carried out on HfB₂-20 vol.% SiC prepared by spark plasma sintering. The dense samples were exposed from 1400 to 2000 °C in an ambient atmosphere for 1 h. For comparison, the same material was tested using an arc jet to simulate an atmospheric reentry environment. The oxidation properties of the samples were determined by measuring the weight gain per unit surface area and the thicknesses of the oxide scale. The oxide scale consists of a SiO₂ outer layer, porous HfO₂ layers, and an HfB₂ layer depleted in SiC. A transition in HfO₂ morphology from equixed to columnar and a decrease in SiO₂ viscosity between 1800 and 1900 °C accompanied a rapid increase in weight gain and scale thickness.     

Effect of seeding on formation of silicon carbide nanostructures from mesoporous silica-carbon nanocomposites

Mesoporous silica-carbon nanocomposites (C-SiO(2)) were synthesized for the fabrication of highly crystalline silicon carbide (SiC) nanoparticles and nanofibers via carbothermal reduction. SiC nuclei were introduced into the mesopores as seeds by infiltration of preceramic precursor polycarbosilane (PCS) prior to the heat treatment of carbothermal reduction. When PCS with a mass percentage of 11-13% was infiltrated into the mesoporous C-SiO(2), SiC nanofibers and nanoparticles were produced at 1450?°C, even in the sample with low carbon content. The major morphology formed from the mesoporous C-SiO(2) nanocomposites without PCS infiltration was nanoparticles, while nanofibers dominated in the products of PCS-infiltrated compositions. The results indicate that the conversion of PCS into SiC nuclei in mesopores prior to carbothermal reduction has facilitated the formation of SiC nanofibers. Therefore infiltration of seeds into mesopores of C-SiO(2) precursors appears to be an effective means of accelerating the reaction and controlling SiC nanostructures.