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1.
用一个计算机控制的倒扭摆研究了快冷Fe71Al29合金中的两个内耗峰.在快冷的Fe71Al29样品中分别在180℃(P1),340 ℃(P2)和510℃(P3)出现了内耗峰,而在慢冷的Fe71Al29样品中只发现了P3峰.快冷样品中的P1和P2峰在从650℃冷却下来的测量过程中或在350℃经过较长时间的时效后消失,其峰高随时效时间的增加 而下降,直至消失.P1和P2峰都有弛豫特征,它们的激活能分别为:H1=1.03±0.08eV(P1峰);H2=1.64±0.05eV(P2峰).P1峰被认为是无序合金中Al原子在四面体点阵内的最近邻运动所引起,P2峰则是无序合金中Al原子在四面体点阵内的次近邻运动所引起.
关键词:
Fe-Al合金
内耗 相似文献
2.
The internal friction of deuterium-doped vanadium has been investigated in the temperature range from 65 to 350 K. At low
deuterium concentrations (≦0.18 at.−%) a relaxation effect has been observed near 90 K; its activation energy and its limiting
relaxation tiem are 0.17 eV and 2×10−12 sec, respectively. A second internal friction peak (precipitation peak) appears in more heavily doped samples; the position
of this second peak shifts to higher temperatures as the deuterium content is increased. Possible mechanisms for the two peaks
are discussed. The phase diagram of the vanadium-deuterium system at low temperatures has been deduced from the correlation
between the deuterium concentration and the position of the precipitation peak. 相似文献
3.
《Physics letters. A》2014,378(30-31):2325-2328
The internal friction is measured in the 4He crystals prepared with the conventional and burst-like methods at temperature 0.65 K and frequency 75 kHz. It is observed that the crystals, grown too rapidly, have an excess damping and smaller dynamic elastic modulus. The magnitude of the effect enhances as the initial overpressure increases. The contribution to the excess damping vanishes at the critical overpressure 3.5 mbar separating the regions of the normal and anomalous crystal growth at the corresponding temperature. Corrections to the modulus and decrement relax with the time constant of about 3 ms. The regime of the burst-like growth may result in the crystals with the internal state different from that of equilibrium crystals. 相似文献
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The long-range diffusion of deuterium in tantalum has been investigated as a function of temperature by means of the anelastic
process due to redistribution of deuterium impurities between compressed and dilated regions of the sample, under an applied
stress alternating at about 4 Hz. The diffusion coefficient was found to obey an Arrhenius-type law in the temperature range
200–390 K; a deviation was observed at lower temperatures. The diffusion parameters in the exponential region areD
0D=(3.3±1.5)×10−4 cm2/s, andW
D=(0.176±0.008) eV. 相似文献
5.
Possible stibnite transformation at the friction surface of the semi-metallic friction composites designed for car brake linings 总被引:1,自引:0,他引:1
V. Matějka Y. Lu P. Matějková B. Smetana J. Kukutschová M. Vaculík V. Tomášek S. Zlá Y. Fan 《Applied Surface Science》2011,258(5):1862
After a friction process several changes in phase composition of friction composites are often registered. High temperature, accompanied by high pressure induced during braking can cause initiation of chemical reactions which do not run at room or elevated temperatures under the atmospheric pressure. Most of the studies in the field of tribochemistry at friction surfaces of automotive semi-metallic brake linings deal with phenolic resin degradation and corrosion of metallic components. The paper addresses the formation of elemental antimony as well as the alloying process of iron with antimony observed on the surface of laboratory prepared semi-metallic friction composites containing stibnite. The role of alumina abrasives in the process of stibnite transformation is also discussed and mechanism of stibnite transformation was outlined. 相似文献
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The microstructures of beech wood and of beech wood-derived carbon, silicon carbide (SiC), and an aluminum/SiC composite were studied using both scanning electron microscopy (SEM) and synchrotron X-ray micro-computed tomography (µCT). As opposed to traditional two-dimensional imaging techniques, the µCT data allowed nondestructive evaluation of relatively large sample volumes. Nondestructive three-dimensional data analysis led to the observation of microstructural features, such as varying pore-wall topographies not previously seen in SEM, calculations of the volume fraction of porosity and characterization of the interconnectivity of porosity in the SiC material. 相似文献
8.
Ali Doğgan 《Pramana》1995,44(5):397-404
The internal friction associated with martensite is calculated using elastic interaction energy between dislocations and solute
atoms in nonlocal elasticity during low temperature aging process. The relaxation strength depends on the lattice parameter
of the crystal as well as the temperature and the heating rate. The peak heights increase with increasing lattice parameter.
The proposed model can demonstrate more realistically the shape of the change of internal friction versus temperature when
nonlocal elasticity is included. 相似文献
9.
采用蒙特卡罗方法, 运用MCNP4C程序研究了碳化硼含量20%–40%、中子能量200 eV–15 keV、材料厚度0.3–2 cm对B4C/Al复合材料中子屏蔽性能的影响. 结果表明: 碳化硼含量与中子透射系数呈一次线性下降关系; 同含量的碳化硼, B4C/Al材料的中子屏蔽效果要大大优于聚乙烯碳化硼材料; 在等厚度条件下, 模拟试样B20等的中子屏蔽效果要优于水、铜、混凝土等常规屏蔽材料; 材料厚度与中子透射系数呈指数下降关系, 且单位厚度的增加对中子透射系数改变很大; 含硼量对热中子透射系数影响很大; 在热中子能区, 中子每单位能量的变化对中子透射系数改变较大; 在慢中子能区, 中子每单位能量的变化对中子透射系数改变很小.
关键词:
中子透射系数
蒙特卡罗
铝基复合材料
碳化硼 相似文献
10.
Longitudinal and transverse wave velocities, eight kinds of elastic parameters, and dilational and shear internal frictions of Zr55Cu30Al10Ni5 glassy alloy were simultaneously measured as a function of temperature in the range from 77 to 373 K, using an ultrasonic pulse method. The inflections at around 150 K for wave velocities, anisotropy factor and Poisson's ratio, and the 150 K peak of shear friction seem to correspond to one topological change (pseudo‐transition) associated with an interatomic readjustment or vacancy rearrangements. The behaviors from 77 to 125 K and 125 to 373 K are due to thermal relaxation of squeezed free volumes and entropy elasticity associated with vibrational motions of clusters, respectively, accompanied by an increase in atomic distance. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Resonant ultrasound spectroscopy was used to study the elastic constants and internal friction of two nanocrystalline palladium samples over the temperature range 3–300 K. The first material, nc-Pd, had a grain size of 80–100 nm and a density 93% of that of single-crystal bulk palladium. The second material, nc-PdSi containing 0.5 at.% Si, had a grain size of 15–22 nm and a density 97% of the single-crystal value. The bulk and shear moduli were significantly reduced in the nc-Pd material from that expected based on single-crystal data, the effect being greater for the bulk modulus. The moduli of nc-PdSi were reduced 4–5% from that based on crystalline Pd. As compared to previous reports of the elastic moduli of nanocrystalline palladium (grain size 5–15 nm) the present values for the larger-grained nc-Pd are comparable, but the present values for the smaller-grained nc-PdSi are considerably higher. An internal friction peak and a modulus defect were found in the nc-Pd material, but not in the nc-PdSi material. These effects are attributed to a relaxation process at the grain boundaries. The temperature dependence of the moduli is similar to that of crystalline palladium and is strongly influenced by electronic effects. 相似文献
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Russian Physics Journal - 相似文献
14.
Based on the MIS model, a simple method to extract parameters of
SiC Schottky diodes is presented using the $I$-$V$ characteristics.
The interface oxide capacitance $C_\i$ is extracted for the first time,
as far as we know. Parameters of 4H-SiC Schottky diodes fabricated
for testing in this paper are: the ideality factor $n$, the series
resistance $R_{\rm s}$, the zero-field barrier height $\phi_{\rm B0}$,
the interface state density $D_{\rm it}$, the interface oxide
capacitance $C_\i$ and the neutral level
of interface states $\phi_0$. 相似文献
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实验研究了探测棒竖直穿过圆筒中颗粒物质运动时所受的滑动摩擦阻力.研究发现,厚度为容器直径的0.5到2倍之间,粒径为2 mm的颗粒堆,对探测棒的滑动摩擦力在一个平均水平上随时间作非线性振动.当探测棒以小于2×10-3 m/s的匀速率上升时,滑动摩擦力平均水平超过初始最大静摩擦力F0的0.2到0.5倍,变化范围可从F0到2F0.频率低于1.35 Hz时,各种频率成分的强度随频率增加按幂函数方式衰减,其主要部分的平均周期T与探测棒运动速率v成反比关系.
关键词:
颗粒物质
滑动摩擦力
非线性振动 相似文献
18.
(Amorphous-)SiC/TiC composites for resistive tubular heaters in HP/HT experiments were obtained via a polymer-precursor process. A slurry consisting of a commercial SiC-precursor polymer (allylhydridopolycarbosilane, AHPCS) and TiC powder as conductive filler was applied to the inner walls of zirconia insulation tubes, using a centrifugation-casting method. Resistive coatings with homogeneous thickness of ~200 μm were obtained. The heaters were tested in octahedral multi-anvil assemblies at ~10 GPa with simultaneous recording of heating voltage and current. Up to a maximum temperature of ~1800°C they showed temperature vs. power characteristics reproducible from batch to batch, with resistance decreasing from 0.08 to 0.02 Ω during heating. Microstructural characterization using SEM/EDX was carried out on the recovered SiC/TiC composite material, as well as on pristine resistive heaters directly after coating and curing to 230°C, and after additional pyrolysis at 900°C in argon. In all cases, a stable composite microstructure of an interpenetrating network of TiC particles with either silicon carbide polymer precursor or an amorphous SiC phase were found. The composites were characterized by XRD and thermogravimetry. Further improvement of coating procedure and materials combination (precursor/filler/insulator substrate) may result in advanced coatings, operational well beyond 2000°C. 相似文献
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用一个计算机控制的倒扭摆研究了快冷Fe71 Al2 9合金中的两个内耗峰 .在快冷的Fe71 Al2 9样品中分别在 180℃(P1 ) ,340℃ (P2 )和 5 10℃ (P3)出现了内耗峰 ,而在慢冷的Fe71 Al2 9样品中只发现了P3峰 .快冷样品中的P1 和P2峰在从 6 5 0℃冷却下来的测量过程中或在 35 0℃经过较长时间的时效后消失 ,其峰高随时效时间的增加而下降 ,直至消失 .P1 和P2 峰都有弛豫特征 ,它们的激活能分别为 :H1 =1.0 3± 0 .0 8eV(P1 峰 ) ;H2 =1.6 4± 0 .0 5eV(P2 峰 ) .P1 峰被认为是无序合金中Al原子在四面体点阵内的最近邻运动所引起 ,P2 峰则是无序合金中Al原子在四面体点阵内的次近邻运动所引起 相似文献