On the application of magneto-optic films in NDE

Some applications of magneto-optic (MO) films in the field of nondestructive evaluation (NDE) are presented. The method for imaging and measuring of magnetic fields on micrometer scale is based on the analysis of changes of the magnetic domain structure caused by the detected field. A process of MO film evaluation and calibration is described. The existence of the leakage field around a fatigue crack in nonmagnetic austenitic material is detected by a highly sensitive MO film. An experimentally determined distribution of the excitation field of an eddy current probe is compared with results obtained by the finite element method (FEM) numerical procedure.     

NDE技术在FGH95粉末材料中的应用

采用超声无损评价技术即NDE技术,对不同的粉末实验件进行了超声检测研究。结果表明,粉末材料中的声速和声衰减是表征材料显微组织的两个重要超声波参量,其中声速与材料的致密性有关,声衰减与材料的晶粒度有关。     

Study of molybdenum precipitation in steels using thermoelectric power measurement

The precipitation of molybdenum in iron has been investigated using thermoelectric power measurement. We found an increase of the thermoelectric power of iron with the molybdenum content and a coefficient of its influence has been determined. A correlation between secondary hardening due to the precipitation of Mo₂C carbides and thermoelectric power variations has been established.     

Detection of surface and subsurface heterogeneities by the hot tip thermoelectric power method

This paper is dedicated to the possibility of using hot tip thermoelectric power (HTTEP) measurement for the detection of surface and subsurface metallic heterogeneities. Depending on the size of the tip, metallic heterogeneities of different sizes and depths can be detected. A numerical simulation based on the resolution of transport equations has been developed in order to test the potentialities of this technique. Simulations and HTTEP measurement obtained on artificial metallic defects in samples are compared. The influence of the nature, size and depth of these heterogeneities on the measured thermoelectric power (TEP) is discussed.     

On thermoelectric figure-of-merit of Pb0.78Sn0.22TeGe solid solution

The investigation results of temperature dependences of thermoelectric parameters in the 140–440 K temperature range are reported for Pb_0.78Sn_0.22TeGe(0.5 at.%) solid solution, having p-type conductivity. The aim is to determine its perspectives as a promising material for thermoelements. Investigations have shown that the temperature dependences of thermoelectric parameters have some interesting features caused by phase transition observed at temperature 290 K.     

Cu effects on radiation embrittlement of Ni-containing complex model alloys and the related potentials of the thermoelectric method

One of the major damage contributions to radiation embrittlement of steels is due to copper precipitation. Precipitation mechanism continues until saturation depending on available amount of precipitants, copper concentration in particular.At the JRC-IE measurement of thermoelectric voltage using a specially developed non-destructive method to assess the embrittlement state of materials are regularly performed. The results analysis, from the test of complex sets of nickel containing alloys with different copper content levels, for both fresh and irradiated conditions, are discussed in this paper with the aim of identifying, if copper precipitation to saturation can be followed by non-destructive measurements. The findings are promising showing that the STEAM non-destructive method has very high potential for studying the copper kinetics part in the radiation embrittlement phenomenon.     

Extrinsic properties affecting the thermoelectric power output of few layer graphene/polyvinylidene fluoride composite thin films

Graphene containing thin film polymer composites possess favorable thermoelectric properties that allow them to be considered for use in low powered applications where durability and weight are important considerations. The use of these materials will be subject to the properties of the specific application, making it necessary to quantify the dependence of the thermoelectric power output on these extrinsic properties. In this study, we show that the power output for a 60 wt% few layer graphene/polyvinylidene composite is dependent on the absolute temperature, temperature difference, and dimensions of the heat source and magnitude of the load resistance. Additionally, the peak power output is achieved when the load resistance matches the internal resistance of the composite. These results demonstrate that it is necessary to optimize the extrinsic properties of the specific application when designing a thermoelectric module to maximize the power output.     

Effect of cooling rate on the thermoelectric and mechanical performance of Bi0.5Sb1.5Te3 prepared under a high magnetic field

Given the thermoelectric and mechanical performance of a given material is closely related to its microstructure, in this paper, the microstructure of p-type Bi_0.5Sb_1.5Te₃, fabricated by a high magnetic field assisted melting-solidification (HMAMS) process, is successfully tuned by regulating the cooling rate during the solidification process, and a systematic investigation has been carried out to the effect of the cooling rate on the crystal orientation, microstructure, thermoelectric and mechanical performance of the obtained materials. By this approach, the thermal conductivity is sharply reduced due to the intensive phonon scattering by the massive BST/Te and Te/BST_Ⅱ interfaces, while the power factor is less affected, and the flexural strength is enhanced owing to the narrowing of eutectic strip and spacing. Eventually, a highest ZT of 1.23 at 323 K with a maximal flexural strength 23.2 MPa has been obtained in the sample prepared under a 6 T magnetic field at a cooling rate of 16 K/min.     

Microstructure and thermoelectric properties of NaxCo2O4/Ag composite synthesized by the polymerized complex method

The synthesis of a thermoelectric Na_xCo₂O₄/Ag composite was attempted by the polymerized complex (PC) process using AgNO₃ as an Ag source and subsequent sintering at 1153 K for 72 ks. The effects of the PC process and Ag addition to Na_xCo₂O₄ on microstructure and thermoelectric properties of the Na_xCo₂O₄/Ag composite were investigated. Ag was hardly substituted for Na and Co sites, and the sintered sample was composed of the Na_xCo₂O₄ and Ag phases. The electrical resistivity of the composite was smaller than that of the Na_xCo₂O₄ single phase and the Seebeck coefficient was slightly enhanced by Ag addition, resulting in the significantly large power factor. However, most of precipitated Ag particles in the Na_xCo₂O₄ matrix were coarse, 5–8 μm in size, and the thermal conductivity of the composite was high as compared to the Na_xCo₂O₄ single phase. From these results, the dimensionless figure of merit of the composite was almost the same as that of the Na_xCo₂O₄ single phase.     

Comparison of the evaluation of the carbon content in solid solution in extra-mild steels by thermoelectric power and by internal friction

The comparison of the evaluation of the carbon content in solid solution in extra-mild steels by thermoelectric power (TEP) and by internal friction (IF) showed the existence of a population of carbon atoms, which is not detected by IF but is visible by TEP. This population, which contributes to the strain ageing, could be constituted of carbon atoms in interaction with substitutional atoms.     

Enhancing the thermoelectric performance of free solidified p-type Bi0.5Sb1.5Te3 alloy by manipulating its parent liquid state

In this work, an irreversible temperature induced liquid–liquid structural transition (TI-LLST) during the heating process was suggested by abnormal resistivity behaviors of Bi_0.5Sb_1.5Te₃ melt. Based on this information, by manipulating the parent liquid state in free solidification, series of explorations were carried out on the solidified structures and TE properties of Bi_0.5Sb_1.5Te₃ alloy. We found that, from the melt after TI-LLST, the solidified microstructures are evidently refined with more Te-rich eutectic strips precipitating on matrix boundaries. More significantly, hierarchical crystal defects are obviously increased, with tinier nanoprecipitates, more subgrains and boundaries, and much more densified lattice distortions. Consequently, the thermal conductivity, especially the lattice thermal conductivity, is decreased notably with the power factor increased moderately at high temperature. In addition, the ambipolar excitation temperature is shifted to higher value and the slope of thermal conductivity vs temperature is also declined. All these alterations contribute to a synergistic enhancement of the TE figure of merit (ZT) and the maximum figure shifts to higher temperature, with ZT_max = 0.78 at 442 K. The present work may provide a new hint for innovating preparation methods of bulk TE materials with simple free solidification.     

The effect of Ag concentration on the structural, electrical and thermal transport behavior of Pb:Te:Ag:Se mixtures and improvement of thermoelectric performance via Cu doping

Pb, Te, Ag and Se, when reacted in a 1:1:x:1 (x = 1.9, 2.0, 2.01) molar ratio, form a two phase composite which consists of a phase which crystallizes in the fcc cubic PbSe structure and a phase that crystallizes in the Ag₂Te structure. In this article, we demonstrate that by varying the Ag concentration, we can manipulate which variant of the Ag₂Te structure stabilizes at room temperature (monoclinic α-Ag₂Te or cubic β-Ag_1.9Te) and can consequently manipulate the electrical and thermal transport behavior of the composite and hence the thermoelectric performance. Additionally, we show that Cu-doping results in an overall improvement in thermoelectric performance. Our results suggest that formation of composites is a viable path for achieving a phonon-glass-electron-crystal (PGEC) alloy.     

β-phase transformation and thermoelectric power in FeSi2 and Fe2Si5 based alloys containing small amounts of Cu

The effects of Cu addition on the β phase formation rate and the thermoelectric power in various FeSi₂ and Fe₂Si₅ based alloys was examined. The peritectoid reaction (a+→β) in FeSi₂ alloys was initially enhanced by the addition of Cu but it became slower for longer annealing times. The retained metallic ε was harmful for the thermoelectric power. The inherent thermoelectric properties of (FeSi₂)_99−XMn₁Cu_X (X=0–1.O at.%), (FeSi₂)_99−X Co₁Cu_X (X=0–1.0 at.%) alloys were attained after the elimination of ε. In the case of eutectoid reaction (→β+Si). Differential thermal analysis, X-ray diffraction and microscopic observation clearly confirmed that the eutectoid reaction rate was drastically enhanced by the addition of a small amount of Cu and its rate decreased with decreasing Cu content. The rate also depends on the annealing temperature and reached a maximum at about 1073 K for most alloys. The addition of only 0.1 at.% Cu was still very effective even in Mn or Co doped alloys. The thermoelectric power of these alloys increased very quickly with annealing time. Their final values decreased with Cu content and saturated at 0.2 at.% Cu. The value of the 0.1 at.% Cu added alloy was higher than that of both the conventional p- and a-type FeSi₂ based alloys. These results suggest that the Fe₂Si₅ alloys with a small amount of Cu may be attractive as new thermoelectric materials.     

The role of temperature gradients in residential copper pipe corrosion

Experiments were conducted to determine the effect of sustained temperature gradients of ≈20 °C on copper pipe corrosion under stagnant conditions in simulated potable water. An apparatus was constructed to (1) apply realistic temperature gradients to the pipes, (2) monitor copper release to the water, and (3) measure thermogalvanic currents between the warm and cold sections of pipe. The orientation of the pipe in relation to the temperature gradients determined whether convection currents developed that promoted mixing during stagnation, and this influenced the magnitude of the temperature gradient in the pipe. The temperature gradient led to significant sustained thermogalvanic currents. Mixing of the water within the pipe also influenced copper leaching and scale build-up.     

Rough集理论在神经网络材料性能参数实时识别中的应用

运用神经网络技术实现材料性能参数的实时识别是智能化拉深的重要研究课题.由于训练样本数据的冗余使得BP网络收敛精度差、速度慢,直接影响到网络的识别精度.运用Rough集理论强大的数据分类简约功能,能够去掉多余属性的样本数据,从而优化了神经网络的拓扑结构.经过试验验证优化后的网络不仅收敛速度快、精度得到极大提高,而且网络预测相对误差精度都在6%以下.     

材料性能参数对液压成形件厚度分布的影响规律研究

厚度分布均匀性是管件液压成形质量的重要评价指标。文章提出了厚度分布均匀性评价指标函数,建立了空心阶梯轴零件的有限元模型,并通过实验验证了仿真结果的有效性。通过模拟研究了材料的应变强化系数K、加工硬化指数n和厚向异性指数R对液压成形管件厚度分布均匀性的影响规律。     

Temperature dependent conductivity and thermoelectric power of the iodine doped poly(vinyl alcohol)–Cu chelate

We have investigated the temperature dependence of electrical conductivity and thermoelectric power (TEP) at 1.7 K < T < 300 K in an organo metallic complex, the iodine doped poly(vinyl alcohol)–Cu²⁺ chelate. We observed intrinsic metallic temperature dependence of resistivity from room temperature to 68 K with a broad minimum [ρ(68 K)/ρ(300 K) 0.75], which has not been observed previously in similar organo metallic complexes. There occurs an unusual metal-insulator transition at T 68 K and the resisitivity increases upon cooling below 68 K. However, the low temperature resistivity becomes finite (instead of going to infinity), [ρ(1.7 K)/ρ(300 K) 0.98] indicating that a quantum mechanical tunneling conduction is dominant at this low temperature. It is remarkable that the resistivity at 1.7 K is as small as that of room temperature. Such unusual temperature dependence of conductivity could be understood as thermally assisted hopping conduction between metallic islands. However, the observed intrinsic metallic temperature dependence of resistivity implies that such hopping conduction barrier is not important at high temperature (T > 68 K). The intrinsic metallic characteristics are confirmed by the quasi-linear temperature dependence of TEP for the whole measured temperature range (1.7 K < T < 300 K) with a small slope change at low temperature, T < 68 K, which is understood as an effect of variable range hopping (VRH) conduction at low temperature. The results of magneto resistance (MR) and magneto thermoelectric power (MTEP) are consistent with the above interpretation.