Sb及Sb-Bi合金在冷却过程中电阻率与结构的变化

通过DSC测试确定了Sb和Sb-Bi合金实现过冷的能力,并且发现放热量随着Sb含量的增加而增加.电阻率的测量结果显示,在冷却过程中,Sb及Sb-Bi合金的电阻率都经历了几次突变,其中Sb及Sb90Bi10处于过冷态时电阻率出现回升现象,并且冷却过程中的温度突变与电阻率突变同时发生.经分析认为,放热量的不同是由于金属释放潜热的能力不同造成的;电阻率出现突变与Sb的斜方六面体结构中的Peicrls畸变及原子团尺寸变化有关;温度突变与电阻率突变相对应说明凝固过程中的结构转变对电阻率有一定的影响.     

添加富铈稀土对低锑合金结构及电化学性能的影响

应用线性电位扫描、计时电势分析法、交流伏安法和腐蚀质量损失法研究在含砷锡的低锑合金中添加混合稀土(85?,10%Y,3%La)对合金性能的影响,利用金相显微镜观察合金的微观组织。结果表明:富铈稀土能细化铅锑合金晶粒,薄化晶界,减少晶体缺陷,降低整体腐蚀速度和腐蚀的危害性;富铈稀土能抑制阳极膜中的PbO生长,生成的PbO也易于还原,降低阳极膜的阻抗,提高板栅合金的深循环性能;当富铈稀土含量为0.5%时,铈与铅生成金属间化合物(PbxCey),锑在合金中分布均匀。     

组成和结构对SiC纤维电阻率的影响(英文)

通过烧成制备电阻率不同的4种SiC纤维,并对纤维的元素组成、结晶性能和表面结构进行分析。结果表明:通过调整不熔化及烧成工艺参数可以获得电阻率量级不同的SiC纤维。当纤维表层具有一定厚度的高富碳层结构时,纤维的电阻率受整体自由碳含量与结晶性能的影响不显著,此时,纤维具有较低的电阻率。富碳层的产生与不熔化纤维烧成时分解产生的烃类小分子的重新裂解沉积有关。通过低温氧化除去纤维表面的富碳层可以使纤维的电阻率增大。表面结构对连续SiC纤维的电阻率有重要影响。     

射频磁控溅射沉积TiAlN薄膜的电阻率温度系数(英文)

TiAlN薄膜是一种有可能作为喷墨打印头中传统的TaN或TaAl发热电阻的替代品。采用TiN和AlN作靶材,在400°C下用射频磁控溅射共沉积方法在Si(100)基底上制备TiAlN薄膜,研究了磁控溅射沉积时等离子体功率密度对TiAlN薄膜电阻率温度系数和抗氧化性能的影响。结果表明,TiAlN薄膜的结晶度、晶粒尺寸和表面粗糙度随着等离子体功率密度的增加而增大,从而导致大晶粒和小晶界。X射线光电子能谱分析得到的Ti、Al和N的键合能表明,TiAlN中氮素化学计量学亏缺使TiAlN薄膜的电阻更大。在最高等离子体功率密度下制备的TiAlN薄膜具有最高的抗氧化性能和最低的电阻率温度系数(765.43×106K1)。     

一种新的补偿硅电阻率/掺杂浓度模型(英文)

硅片或硅块的电阻率与掺杂浓度的关系模型不适用于补偿硅,如精纯冶金级硅(UMG-Si)。目前尚无合适的理论模型可以准确解释补偿硅实验和观测结果间存在的差异。基于电解液理论提出一种包含电离平衡常数的新方法,可以得到单掺杂硅的电荷载子迁移率Thurber曲线。当掺杂硅中包含一种以上掺杂物质时,需要采用数值算法来解决多重平衡系统。研究表明这类系统表现出一种缓冲溶液的特定行为。通过计算化合物的热力学参数获得平衡常数,并利用现有的电化学知识(Nerust方程和Butler-Volmer方程)提出一个普遍理论。因为硅/掺杂物系统构成一个弱电解质固溶体,电解质溶液理论为太阳能电池行为的认知提供了一个很好的物理模型和数学框架。     

基于二维高密度电阻率数据的二、三维反演对比(英文)

目前高密度电阻率法所采用的数据处理方法主要是将地质结构体视为二度体进行二维处理,因而二维数据资料处理结果只是一种近似解释,其计算精度与反演效果达不到精确反演的要求。设计两种典型的电阻率异常地质体模型,利用有限单元法进行正演计算。为更真实地模拟实测数据并分析二维、三维反演算法对噪声的敏感度,在正演剖面中加入1%的高斯随机误差,然后再分别利用最小二乘法进行高密度电阻率法二维、三维反演。对比二维和三维高密度电阻率法的反演水平切片及垂直切片图可知,三维反演受高斯随机误差的影响更小,反演结果在模型异常位置、形态和电阻率特性反映上都比二维反演的效果更好,与实际地质模型更接近。     

过冷液态和非晶态金属Pb等温驰豫过程中bcc相的形成和演变特性(英文)

采用分子动力学模拟方法和团簇类型指数法,对过冷液态和非晶态金属Pb在等温驰豫过程中bcc相的形成和演变特性进行研究。结果表明:bcc相的形成和演变密切依赖等温驰豫过程的初始温度和初始结构,在过冷液态区,bcc相很容易形成并在模拟时间范围内保持稳定;而在非晶态区,bcc相先形成并随后部分转变为hcp相,当驰豫的初始温度在较低的153K和113K时,hcp和fcc相不经历亚稳bcc相而直接在非晶态结构中形成;这说明Ostwald的"步进原则"在过冷液态和非晶态Pb等温驰豫过程中是有效的,并且,亚稳bcc相起到重要的晶化前驱的作用。     

Bi_2Te_(2.55)Se_(0.45)合金熔体电阻率及凝固与熔体状态相关性的探索

探索了Bi2Te2.55Se0.45热电材料熔体的电阻率温度行为,并在此基础上,采用热分析法、金相分析、X射线衍射、SEM和EDS等表征手段研究了不同熔体状态对Bi2Te2.55Se0.45合金凝固行为和组织的影响。结果所示,Bi2Te2.55Se0.45合金熔体升温过程中在840~940℃的范围内存在温度诱导不可逆液-液结构转变。凝固结果表明,熔体结构转变后合金熔体的凝固行为和组织与转变前熔体的凝固情况有明显差别,如形核和生长过冷度分别增加了17.6℃和2.2℃,形核率明显提高,凝固时间缩短了8 s,凝固组织明显细化,且分布更为均匀;此外,熔体状态的改变使合金XRD特征峰向高角度偏移,沿(00l)晶面的择优取向明显减弱。     

Al-0.96Mg_2Si合金时效过程亚稳相析出行为及其对合金电阻率的影响(英文)

采用原位电阻率测试和透射电镜观察研究Al-0.96Mg2Si合金的析出行为及其对电阻率的影响。发现峰值时效的析出相包括β″和β′,而他们的比例随着时效温度和时间的改变而变化。合金在175°C峰值时效内的析出相主要是针状β″相(也包括pre-β″)。这些析出相会随着时效时间的延长而长大,但是进一步延长时效时间至超出峰值时效时间后,析出相的尺寸变化并不显著。合金电导率的变化规律与之类似。合金硬度峰值时效后,继续时效很长一段时间硬度变化都不显著。由于温度是影响β″/β′比的主要因素,因此时效温度也是影响电阻率的主要因素。时效温度越高β″/β′的比值越小,ρ下降的速度就越快。硬度也随着该比值的减小而降低。通过对透射电镜照片分析获得析出相的分布参数,建立了析出相与电阻率之间的半定量关系式。     

熔体快淬Cu100-xCrx合金过饱和固溶体的时效分解及对电阻率的影响

用熔体快淬法制备了C11100-xCrx(x=2～35)合金带.研究表明:熔体快淬带的组织由Cr在Cu中的过饱和固溶体、富Cr溶质偏聚区、富Cr液相分解粒子组成;含Cr量增加,液相分解粒子体积分数增加,电阻率提高;过饱和固溶体在等温时效过程中短时间内(10 min)快速分解完毕,合金带的电阻率大幅下降,延长时效时间,富Cr沉淀相尺寸长大缓慢;时效温度升高,富Cr沉淀的尺寸略有增大,电阻率在600℃时效达到最小值.     

二元SnZn合金的电阻随温度变化的特性

采用直流四电极法研究了常压下Sn-Zn合金系的电阻率随温度连续升温的变化规律。结果表明:合金Sn-Zn5、Sn-Zn8.8、Sn-Zn20、Sn-Zn30、Sn-Zn40、Sn-Zn50和Sn-Zn70分别在970、1 008、957、950、948、926和873℃处发生了电阻率的突变现象。对合金的进一步分析表明,Sn-Zn熔体电阻率在高温时的突变是由Zn在Sn-Zn熔体中大量汽化造成的,即在此处发生了液气结构转变;Sn-Zn合金在完全熔化至发生液气结构转变的连续升温过程中,合金中并不存在某种液液结构的转变,且液液结构转变并非存在于在所有二元合金系中。     

Effect of nonlinear liquidus and solidus on dendrite growth in bulk undercooled melts

On the base of nonlinear liquidus and solidus,an extended model for dendrite growth in bulk undercooled melts was developed under local non-equilibrium conditions both at the interface and in the bulk liquid.In terms of thermodynamic calculations of the phase diagram,the model predictions are relatively realistic physically,since few fitting parameters are used in the model predictions.Adopting three characteristic velocities,i.e.the critical velocity of absolute solute stability(VC*),the velocity of maxima...     

Electrical resistivity and structural heredity of hypereutectic Al-Si alloy melt

1　INTRODUCTIONAgreatamountofpracticeprovesthat ,aftertheoriginalchargesareremelted ,themeltstatehashereditaryeffectsonthesolidificationstructurenewlyobtained .Hereditycanbeconsideredfrom generalsenseasthetransformationofthesimilaritiesinthestructureorphysicalpropertiesfromtheoriginalob jectstothesecondaryones .Moreover ,itissuitablefordescribingpropertiesthatcorrelatewiththepro cesswhichthealloysamplesexperiencedinsteadofpropertiesofalloystatefunctions .Whilestudyingthestructuralheredity…     

Twinning stress in shape memory alloys: Theory and experiments

Utilizing first-principles atomistic simulations we present a twin nucleation model based on the Peierls–Nabarro formulation. We investigated twinning in several important shape memory alloys, starting with Ni₂FeGa (14M modulated monoclinic and L1₀ crystals) to illustrate the methodology, and predicted the twin stress in Ni₂MnGa, NiTi, Co₂NiGa, and Co₂NiAl martensites, all of which were in excellent agreement with the experimental results. Minimization of the total energy led to determination of the twinning stress accounting for the twinning energy landscape in the presence of interacting multiple twin dislocations and disregistry profiles at the dislocation core. The validity of the model was confirmed by determining the twinning stress from experiments on Ni₂FeGa (14M and L1₀), NiTi, and Ni₂MnGa and utilizing results from the literature for Co₂NiGa and Co₂NiAl martensites. This paper demonstrates that the predicted twinning stress can vary from 3.5 MPa in 10M Ni₂MnGa to 129 MPa for the B19′ NiTi case, consistent with the experimental results.     

Variability in Co2 Oxidation Resistance of 2 1/4 Cr 1 Mo and 1 Cr 1/2 Mo Steels

Abstract

Oxidation tests in CO₂ atmospheres on nominally identical casts of low alloy steels have revealed wide variation in oxidation resistance. A study has been made of the influence of chemical composition, mechanical and thermal treatment, and remelting on the CO₂ oxidation behaviour of steels of the 21/4 Cr 1 Mo and 1 Cr 1/2 Mo type.

Statistical analyses of CO₂ oxidation results have shown a strong positive correlation of oxidation rate with sulphur content in certain instances, but a number of anomalies have been found. A similar relationship has been obtained between ‘MnS’ content and oxidation rate by area count studies of the inclusions in a range of 2 1/4 Cr 1 Mo steels. These have also indicated a possible effect of ‘MnS’ particle size and particle size distribution which could account for some of the anomalous results obtained in the statistical work. Conventional solid state heat treatments appear to have no significant effect on the oxidation behaviour of 2 1/2 Cr 1 Mo and while remelting in argon did not generally improve oxidation behaviour, remelting in vacuo followed by forging and rolling resulted in a material of high oxidation resistance.     

Corrosion behavior of UCX,KHR35, and KHR45 alloys in molten nitrates

The corrosion behavior of three high-Ni, high-Cr alloys, that is, UCX, KHR35, and KHR45 alloys, in a mixture of 60% NaNO₃–40% KNO₃ at 600°C has been evaluated by using weight loss tests, potentiodynamic polarization curves, and electrochemical impedance spectroscopy measurements. Cr contents ranged between 23.25 and 43.2 wt.%, whereas Ni ranged between 36.6 and 50.3 wt.%. For comparison, the same studies were performed on 304-type stainless steel (304SS). Tests were complemented with detailed scanning electronic microscope and X-ray diffraction studies. Results showed that that the three high-Ni, high-Cr alloys had lower weight loss than that for 304SS. Polarization tests indicated the formation of a passive layer in all cases. Electrochemical impedance spectroscopy data have shown that the corrosion mechanism for all the alloys was charge transfer from the alloy to the molten salt. Finally, X-ray patterns showed the presence of Cr₂O₃ in all tested alloys, which is responsible for the observed passive behavior and their corrosion resistance.     

Martensitic transformation and anomalies in resistivity of (Ti–50Ni)1−xCx (x = 0.1, 0.5 at.%) shape memory alloys

Phase transformation of solid solution (Ti–50Ni)_1−xC_x (x = 0.1, 0.5 at.%) alloys have been studied by using differential scanning calorimetry, physical property measurement system and optical microscope. The transformation temperature decreases due to the existence of titanium carbide (TiC) particles compared with that of near-equiatomic Ti–Ni shape memory alloy. The resistivity vs. temperature curves show hysteresis. Thermoelastic martensitic transformation occurred in two alloys despite the difference in TiC content. Nevertheless, the resistivity results show different martensitic transformation routes. A one-step B2 → B19′ transformation occurred in the low TiC content alloy and an R transformation appeared in another alloy, suggesting that the martensitic transformation routes depended on the TiC content. The cumulative effect of the TiC particles causes the local stress field and lattice distortion to restrain the transformation of the B19′. On the other hand, the TiC content has an effect on the temperature coefficient of electrical resistivity (TCR) of alloys. The Ti–Ni–0.5C alloy shows a negative TCR in the range 100–300 K during which transformation occurs. Another alloy shows the opposite result. The cause of the negative TCR is briefly discussed.     

Electrical resistivity,Curie temperature and band structure in Tb0.27Dy0.73(Fe1−xCox)2 intermetallics

Electrical resistivity studies performed in a wide temperature range across the complete Fe/Co substituted Tb_0.27Dy_0.73(Fe_1−xCo_x)₂ intermetallic series, with a borderline compound Tb_0.27Dy_0.73Fe₂ known as Terfenol-D are presented. Parameters characterizing the dependence of resistivity on temperature, including the Debye temperature, are determined. Residual, phonon and magnetic contributions are separated from electrical resistivity. The magnetic contribution to electrical resistivity is applied to estimate Curie temperatures. Regions of weak and strong ferromagnetism of the transition metal sublattice are evidenced. The Curie temperature increases with x, approaches a maximum for x = 0.3 and reduces across the rest of the series. Some results of electronic band structure calculations using the Full-Potential Linearized Augmented Plane Waves (FLAPW) method are also presented. A distribution function for the densities of 3d states is introduced and a formula to estimate the band splitting energy is proposed. The obtained 3d and 4s band splitting energies for iron, cobalt and average for transition metal are presented. The Curie temperature across the Tb_0.27Dy_0.73(Fe_1−xCo_x)₂ system is described using a formula relating to both the FLAPW calculated magnetic moments and the statistical properties of the substituted transition metal sublattice.