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为了考察材料晶体学特性对表面熔坑形成机制的影响,利用强流脉冲电子束(HCPEB)对喷丸前、后的304奥氏体不锈钢进行表面辐照处理,对HCPEB诱发的表面熔坑形貌进行了详细的表征。实验结果表明,HCPEB辐照后样品表面形成了大量的火山状熔坑,熔坑数密度和熔坑尺寸随电子束能量的增加而减小,材料表面的杂质或夹杂物容易成为熔坑的核心,并在熔坑形成的喷发过程中被清除,起到净化表面的作用。此外,喷丸前、后样品表面熔坑数密度遵循相似的分布规律,喷丸处理使熔坑数密度显著增大,表明材料的晶体学特性对表面熔坑形成有重要的影响,晶界、位错等结构缺陷是熔坑形核的择优位置。 相似文献
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随着超高速动能武器的发展,长杆弹超高速侵彻混凝土靶机理成为当前的研究热点。为了探究长杆弹超高速侵彻混凝土靶的侵彻机理和开坑规律,本文中开展了TU1铜、Q235钢两类长杆弹以初速度1.8~2.4 km/s正侵彻强度26.5、42.1 MPa混凝土靶的超高速实验。结合文献和本文中的实验数据,对开坑直径和开坑体积进行量纲分析,基于开坑截面的弓形形貌几何关系,得到了开坑深度预测公式。结果表明:靶面开坑尺寸明显大于中低速侵彻时的靶面开坑尺寸,在分析侵彻机理的过程中不能忽略开坑阶段;弹体发生严重的长度缩短,直至最后完全侵蚀,弹洞半径明显大于弹体半径,说明长杆弹超高速侵彻半无限混凝土靶属于半流体侵彻机制。另外,在超高速侵彻条件下:弹体长度是影响侵彻深度的最主要参数;侵彻深度随弹体长度和密度的增大而增大,受弹体强度影响不大。
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Samples from vesicular Lonar impactite have been investigated by Mössbauer spectroscopy and SEM in combination with elemental analysis. Observation reveal the new-formation of oxide minerals have occurred with nucleation in particular at the walls of the vesicles interpreted as having formed from condensation of the gas phase having caused the vesicles to form in the first place. Elemental analysis of Ti-magnetites gives very similar compositions irrespective of the oxides grains being vesicle or matrix associated (Fe/Ti ratios approximately 3). The room temperature spectra of the oxides show magnetically ordered components due to A, B, and C sites in the substituted spinel. The occurrence of these ordered components are not in accordance with expectations from the bulk chemical compositions, suggesting the presence of fine scaled intergrowth of Ti-oxide and Ti-magnetite. 相似文献
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Shockwave and spallation in silver and other materials by sub-ns laser pulse at 1016 W/cm2 intensity
The laser spallation effect due to intense shockwaves caused by a brief and intense laser pulse irradiating a target surface, 2 mm thick, has been investigated for silver and other materials. For 300 ps IR laser pulse, at intensities of the order of 1016 W/cm2, the shockwave may produce deformations of the back-face in ductile materials, such as Ag, Cu and Al. In heavy materials with high tensile strength, such as Ta, the shockwave produces cracks in the bottom of the laser crater but not deformation in the back-face, while in brittle materials, such as monocrystalline Ge, it produces only superficial cracks and flaking, but not deformation and spallation of the back-face. In thick polymeric materials, such as high-density polyethylene, the ablated crater shape is well defined and the shockwave is strongly damped, and no deformation has been observed in the back-face. The laser ablation yield and the ion acceleration in the backward direction have been measured by mass lost and time-of-flight measurements. SEM microscopy of the different irradiated targets, showing details of the crater size, edges, flaking and deformation in the back-face, useful for a discussion on the shockwave propagation and shock pressure calculation, is presented. 相似文献
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A. Tani C. Yamanaka M. Ikeya O. Ohtaka M. Takada T. Katsura 《Radiation measurements》2000,32(5-6):473-477
Optically stimulated luminescence (OSL) of synthetic stishovite was investigated for a future dating technique of meteor impact craters. Luminescence around 330 nm was measured on the γ-ray irradiated stishovite under two stimulating light sources of infrared laser (830 nm) and blue light emitting diode set (470 nm). Thermoluminescence (TL) studies before and after the OSL measurements showed the intensities around 100–200°C and 220–350°C to increase and those around 350–450°C to decrease. This indicates that a part of deep-trapped charges excited during the OSL measurements were retrapped by shallower traps. The infrared stimulated luminescence (IRSL) after the TL measurement up to 450°C could not be detected, while the blue light stimulated luminescence (BLSL) after TL had about one-tenth of the intensity before TL. This indicates that a part of the charges in shallower traps were detrapped thermally and returned to the deeper traps which were related to BLSL. The result implies that some of the BLSL-related traps are quite stable at room temperature and could be used for geological dating. In addition, two paramagnetic centers produced by sudden release of high pressure in synthesis process were found in the unirradiated stishovite by electron spin resonance (ESR). Their g-factors are g=2.00181 and g=2.00062 for an axial signal and g=2.00305 for the other isotropic signal. These signals could be used for an evidence of impacts if those signals could be stored in geological time. 相似文献
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Cobalt-60 gamma ray induced polymerization of vinylidine chloride has been studied, as an example of precipitating type of polymers. The percentage conversion of the monomer was not linear with the absorbed dose but showed acceleration. By studying the initial part of the curve which was linear, the initial rates of polymerization have been determined for different temperatures and dose rates. The dose rate exponent was found to be 0.48, and the energy of activation was observed to be 7.4 kcal/mol. The radical yield was determined by competition reaction with a stable free radical DPPH using the induction period method and GR was found to be 21.0. The intrinsic viscosities of the polymers have been determined in o-dichlorobenzene at 120°C. The results show a maximum in molecular weight as the radiation dose is increased. These results as well as the results on the dose rate exponent, and energy of activation are discussed. 相似文献
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采用非火药驱动二级轻气炮发射球形弹丸,对单层5A06铝合金板进行高速撞击实验研究,从而模拟空间碎片对航天器防护结构的高速撞击作用。实验得到了该铝合金板在不同的速度区间的损伤模式。结果表明,弹丸撞击速度一定时,弹坑深度和弹坑直径均与弹丸直径呈线性关系。当撞击速度在4km/s至5km/s时,靶板上的弹坑深度和弹坑直径随撞击速度的增大而减小,在其它速度范围内,弹坑深度和弹坑直径随撞击速度的增大而增大。通过固定弹丸直径,变化撞击速度,寻找临界撞击速度的方法获得了该铝合金板在弹丸撞击速度为1.0km/s至4.2km/s时的撞击极限曲线,并将实验弹坑深度与由Cour-Palais方程得到的预测弹坑深度进行了比较,实验弹坑深度大于预测值。 相似文献
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Low temperature plasma for the preparation of crater walls for compositional depth profiling of thin inorganic multilayers
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An indirect, compositional depth profiling of an inorganic multilayer system using a helium low temperature plasma (LTP) containing 0.2% (v/v) SF6 was evaluated. A model multilayer system consisting of four 10 nm layers of silicon separated by four 50 nm layers of tungsten was plasma‐etched for (10, 20, 30) s at substrate temperatures of (50, 75, and 100) °C to obtain crater walls with exposed silicon layers that were then visualized using time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) to determine plasma‐etching conditions that produced optimum depth resolutions. At a substrate temperature of 100 °C and an etch time of 10 s, the FWHM of the second, third, and fourth Si layers were (6.4, 10.9, and 12.5) nm, respectively, while the 1/e decay lengths were (2.5, 3.7, and 3.9) nm, matching those obtained from a SIMS depth profile. Though artifacts remain that contribute to degraded depth resolutions, a few experimental parameters have been identified that could be used to reduce their contributions. Further studies are needed, but as long as the artifacts can be controlled, plasma etching was found to be an effective method for preparing samples for compositional depth profiling of both organic and inorganic films, which could pave the way for an indirect depth profile analysis of inorganic–organic hybrid structures that have recently evolved into innovative next‐generation materials. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献