应变率对V-5Cr-5Ti合金拉伸性能的影响

应用旋转圆盘冲击拉伸Hopkinson试验装置和MTS材料试验机,测定了V-5Cr-5Ti合金在不同应变率下的拉伸性能,用SEM观察了断口形貌,获得了10-5s-1~103s-1应变率范围内V-5Cr-5Ti合金的拉伸应力应变关系。结果表明V-5Cr-5Ti合金为应变率敏感材料,流动应力随应变率的增加而增加,且发生韧脆转变现象,其韧脆转变临界应变率在101s-1~102s-1量级。     

Ti-6Cr-5Mo-5V-4Al合金热加工性能研究

目的 基于应变速率敏感系数、温度敏感系数,研究Ti-6Cr-5Mo-5V-4Al(Ti-6554)合金的热加工性能。方法 通过Gleeble-3500热模拟实验机,在温度为953~1 043 K、应变速率为0.001~10 s^?1时,对Ti-6Cr-5Mo-5V-4Al合金进行高温压缩实验。建立不同应变下的应变速率敏感系数图、温度敏感系数图,分析不同变形条件下的微观组织。结果 随着应变速率的增加,应变速率敏感系数逐渐下降,而低温度敏感系数区域主要集中在低应变速率区域。基于微观组织表征,发现变形过程中存在明显的动态相变和动态再结晶过程。结论 确定Ti-6554合金的合理加工条件为953~964 K、0.001 s^?1和1 037~1 043 K、0.001 s^?1。     

电子束熔炼钒合金动态压缩实验及细观分析

本文利用霍普金森压杆(SHPB)进行了动态压缩实验,获得了电子束熔炼钒合金V-5Cr-5Ti的动态压缩应力应变曲线。采用应变冻结的方法,对材料进行不同变形量的动态加载,并对加载后的试件进行观察,研究不同变形范围下材料的细观变形机制,考察变形量对变形机制的影响,并与电弧熔炼钒合金的细观变形机制进行了比较。结果表明:当动态压缩应变率为3600s-1时,电子束熔炼钒合金的流变应力约为700MPa;该材料在常温下的塑性变形机制为位错滑移。     

温度对V-5Cr-5Ti合金拉伸性能及组织结构的影响

对真空自耗重熔制备的V-5Cr-5Ti合金进行了室温到1150℃温度范围的拉伸性能测试,获得了不同温度下的拉伸应力应变曲线,用SEM和光学显微镜对断口形貌和金相组织进行了观察,分析了温度对断口形貌和组织的影响。结果表明:V-5Cr-5Ti合金的屈服强度和极限强度总体上随温度升高而降低,但在300℃到700℃之间出现应变失效效应,断裂伸长率随温度升高而降低,断面收缩率随温度升高先增大再而降低,在400℃时断面收缩率最大;温度较低时塑性变形以滑移为主,温度较高时以晶界开裂为主,并伴随有晶界熔化的现象,高温断口表现为韧性断裂为主,具有韧性与脆性共存的现象。     

退火处理对V-5Cr-5Ti合金微观组织和硬度的影响

研究了拉伸变形后V-5Cr-5Ti合金硬度和微观组织随退火温度的变化,并对微量杂质元素的影响进行了深入分析.在真空炉中进行退火,利用万能实验机和维氏硬度计进行拉伸变形和硬度测试,采用X射线衍射(XRD)分析相结构,扫描电镜(SEM)和光学显微镜(()M)观察微观组织.研究结果表明,拉伸变形后V-5Cr-5Ti合金的硬度...     

V-5Cr-5Ti合金富钛相析出区的显微维氏硬度测试

为探索利用金属显微维氏硬度计测试合金微区成分偏聚区硬度变化的可行性,采用金属显微维氏硬度计,结合纳米压痕试验技术和激光共焦显微镜压痕深度轮廓曲线测量法,测试了V-5Cr-5Ti合金富钛相析出区的硬度变化。结果表明:机械磨光使V-5Cr-5Ti合金试样表面形成明显的硬化层,采用草酸水溶液的电解蚀刻方法不仅能显示出完整的组织特征,还可以有效去除该硬化层,合金中富钛相析出区比非析出区的硬度提高约12%。     

固溶温度对Ti-5Mo-5V-2Cr-3Al钛合金棒材组织和性能的影响规律

研究了固溶温度对Ti-5Mo-5V-2Cr-3Al钛合金棒材显微组织和力学性能的影响。结果表明,钛合金固溶处理温度在相变点以下,空冷后,显微组织由β相、初生α相以及次生α相组成。随着固溶温度的升高,显微组织中β相晶粒尺寸增大,晶界α相厚度减小,产生有序化现象,而次生α相数量和尺寸减小,使合金的强度降低,塑性升高,但固溶处理温度为800℃时,网状晶界α相使塑性迅速下降;当固溶处理温度在相变点以上,Ti-5Mo-5V-2Cr-3Al钛合金重新形核并长大,随着固溶温度的升高,β相晶粒尺寸增大,初生α相数量减少,强度和塑性都下降,过冷β相晶粒发生应力诱发马氏体现象。     

Ti-5Mo-5V-1Cr-3Al合金的热压缩变形行为研究EI北大核心CSCD

采用恒应变速率热压缩模拟实验,对Ti-5Mo-5V-1Cr-3A1（简称1Cr）钛合金在应变速率0.001～1s-1、变形温度700～900℃条件下进行研究.结果表明：该材料的流变应力对温度与应变速率敏感：当变形温度为700～800℃时,真应力-真应变曲线呈现动态再结晶单曲线特征;当变形温度为800～900℃时,低应变速率（0.001s-1）的真应力-真应变曲线呈现动态再结晶多应力峰值曲线特征,高应变速率（0.01～1s-1）的真应力-真应变曲线呈现动态回复曲线特征.1Cr合金在等温压缩变形时的流变行为可用包含Zener-Holomon参数的Arrhenius本构方程描述,变形激活能为456kJ/mol.金相结果显示,材料在热压缩过程中的动态行为除了与变形速率、变形温度等加工参数相关外,也与相应温度、变形速率下材料的组织及相结构有关.合金在低应变速率0.001s 1下热压缩变形时,在接近相变点或以上（800～900℃）温度范围内仍呈现动态再结晶行为,这与材料在此阶段发生的应变诱发马氏体转变密切相关,马氏体相的析出促使材料在热变形时趋向于发生动态再结晶行为.     

Nb47Ti合金热变形行为及微观组织

目的 研究Nb47Ti合金在变形温度为600～750℃、应变速率为0.001～1s?1条件下的热变形行为和微观组织。方法 采用Gleeble-3500型热/力模拟试验机进行等温恒应变速率压缩实验,获得Nb47Ti合金热变形的真应力应变曲线,并利用EBSD技术手段分析热变形后的微观组织。结果 Nb47Ti合金在变形温度小于650℃、应变速率小于0.1s?1下热变形的真应力-应变曲线为动态再结晶型曲线,变形温度大于等于700℃时呈现为动态回复型曲线;峰值应力随变形温度的升高和应变速率的减小而减小;在变形温度为650℃、应变速率为0.001 s?1下热变形组织以再结晶晶粒和亚晶粒为主,随着应变速率的增大,动态再结晶晶粒不断减少,而亚晶粒和变形晶粒增多,晶粒得到显著细化。当应变速率为0.1 s?1时,随着变形温度的增加,晶粒尺寸增大,变形温度升高至750℃,热变形组织中亚晶粒所占比例高达50.5%。结论 Nb47Ti合金是温度和正应变速率敏感材料,随变形温度的升高和应变速率的增大,变形过程中动态回复软化机制更为显著,低温、高应变速率下变形获得的再结晶晶粒尺寸小。     

高能球磨Gd5Si1.8Ge1.8Si0.4合金的磁性能及相组成

采用电弧熔炼的方法制备了具有一级磁晶相变Gd5Si1.8Ge1.8Si0.4母合金,然后在不同时间条件下对其进行高能球磨,并研究球磨时间对该磁热合金的磁性能及相组成的影响.粉末XRD结果显示球磨没有改变Gd5Si2Ge2相,但拓宽了相应的布拉格衍射峰,这表明球磨后的合金的晶粒尺寸较小.另外,球磨后的合金中形成了一些非晶相.随着晶粒尺寸和磁畴的减小,与母合金相比,希望其滞后现象减小.     

Thermodynamic properties of Pt5La,Pt5Ce,Pt5Pr,Pt5Tb and Pt5 Tm intermetallics

The Gibbs’ energies of formation of Pt₅La, Pt₅Ce, Pt₅Pr, Pt₅Tb and Pt₅ Tm intermetallic compounds have been determined in the temperature range 870–1100 K using the solid state cell: $$Ta,M + MF_3 /CaF_2 /Pt_5 M + Pt + MF_3 ,Ta$$ . The reversible emf of the cell is directly related to the Gibbs’ energy of formation of the Pt₅M compound. The results can be summarized by the equations: $$\begin{gathered} \Delta G_f^ \circ \left\langle {Pt_5 La} \right\rangle = - 373,150 + 6 \cdot 60 T\left( { \pm 300} \right)J mol^{ - 1} \hfill \\ \Delta G_f^ \circ \left\langle {Pt_5 Ce} \right\rangle = - 367,070 + 5 \cdot 79 T\left( { \pm 300} \right)J mol^{ - 1} \hfill \\ \Delta G_f^ \circ \left\langle {Pt_5 Pr} \right\rangle = - 370,540 + 4 \cdot 69 T\left( { \pm 300} \right)J mol^{ - 1} \hfill \\ \Delta G_f^ \circ \left\langle {Pt_5 Tb} \right\rangle = - 372,280 + 4 \cdot 11 T\left( { \pm 300} \right)J mol^{ - 1} \hfill \\ \Delta G_f^ \circ \left\langle {Pt_5 Tm} \right\rangle = - 368,230 + 4 \cdot 89 T\left( { \pm 300} \right)J mol^{ - 1} \hfill \\ \end{gathered} $$ relative to the low temperature allotropic form of the lanthanide element and solid platinum as standard states The enthalpies of formation of all the Pt₅M intermetallic compounds obtained in this study are in good agreement with Miedema’s model. The experimental values are more negative than those calculated using the model. The variation of the thermodynamic properties of Pt₅M compounds with atomic number of the lanthanide element is discussed in relation to valence state and molar volume.     

Fe86Zr5.5 Nb5.5 B3非晶合金的超高压烧结成型

为了获得致密的块状Fe86Zr55Nb55B3纳米晶合金,研究了高压快速烧结工艺参数对样品致密度和α-Fe相晶粒尺寸的影响.结果表明:快淬球磨破碎非晶粉末在5.5 GPa/3min烧结条件下,当Pw=1150 W后,可获得相对密度为98.3%、单相α-Fe纳米晶(16.3 nm)块体合金,且随着Pw和t的增加,样品相对密度和α-Fe相晶粒尺寸均略有增加,样品典型的比饱和磁化强度σs和矫顽力Hc分别为119.6 emu/g,63.8 Oe.     

Synthesis of tritium-labeled 5-fluorouracil and 5-fluorocytosine

The effect of various catalysts and temperature on the solid-phase isotope exchange of 5-fluorouracil and 5-fluorocytosine with tritium was studied. The isotope exchange yielding the desired compounds is accompanied by dehalogenation and hydrogenation of the 5,6-double bond of the pyrimidine ring. Performing the reaction at a temperature below 160°C allowed the process to be carried out selectively, i.e., with the preservation of the functional groups and double bond in the starting compound. The yields of various products formed in the reactions of tritium with the above compounds were estimated. Synthesis conditions were found, and tritium-labeled 5-fluorouracil and 5-fluorocytosine were prepared with the molar radioactivity of 0.45 Ci mmol⁻¹ (16.7 TBq mol⁻¹) and 4.4 Ci mmol⁻¹ (0.16 PBq mol⁻¹), respectively, and with the purity exceeding 98%.     

GAMS5

The construction of the double-crystal γ-spectrometer GAMS5 was finished recently and the instrument is now operational. Measurements with double flat crystals were carried out and we will report here on the progress concerning the characteristics of the spectrometer.     

Thermoluminescence solid-state nanodosimetry--the peak 5A/5 dosemeter

The shape of composite peak 5 in the glow curve of LiF:Mg,Ti (TLD-100) following (90)Sr/(90)Y beta irradiation, previously demonstrated to be dependent on the cooling rate used in the 400°C pre-irradiation anneal, is shown to be dependent on ionisation density in both naturally cooled and slow-cooled samples. Following heavy-charged particle high-ionisation density (HID) irradiation, the temperature of composite peak 5 decreases by ～5°C and the peak becomes broader. This behaviour is attributed to an increase in the relative intensity of peak 5a (a low-temperature satellite of peak 5). The relative intensity of peak 5a is estimated using a computerised glow curve deconvolution code based on first-order kinetics. The analysis uses kinetic parameters for peaks 4 and 5 determined from ancillary measurements resulting in nearly 'single-glow peak' curves for both the peaks. In the slow-cooled samples, owing to the increased relative intensity of peak 5a compared with the naturally cooled samples, the precision of the measurement of the 5a/5 intensity ratio is found to be ～15% (1 SD) compared with ～25% for the naturally cooled samples. The ratio of peak 5a/5 in the slow-cooled samples is found to increase systematically and gradually through a variety of radiation fields from a minimum value of 0.13±0.02 for (90)Sr/(90)Y low-ionisation density irradiations to a maximum value of ～0.8 for 20 MeV Cu and I ion HID irradiations. Irradiation by low-energy electrons of energy 0.1-1.5 keV results in values between 1.27 and 0.95, respectively. The increasing values of the ratio of peak 5a/5 with increasing ionisation density demonstrate the viability of the concept of the peak 5a/5 nanodosemeter and its potential in the measurement of average ionisation density in a 'nanoscopic' mass containing the trapping centre/luminescent centre spatially correlated molecule giving rise to composite peak 5.     

Characterization of coprecipitated ferroelectric Bi2 VO5·5

Fine powders of orthorhombic bismuth vanadate (Bi₂ VO_5·5) have been synthesized by coprecipitation method. Powder X-ray diffraction and electron microscopic techniques have been used to characterize these samples. The formation of the monophasic Bi₂ VO_5·5 was confirmed. The compacted powders sintered at 1070K have been characterized for their dielectric properties as a function of both temperature (300–900 K) and frequency (100 Hz–10 MHz) and found to be superior to those obtained by the conventional solid-state reaction route.     

Evolution of the structure of Ti-5Al-5Mo-5V alloy deformed by high pressure

Specific features of straining of the Ti-5Al-5Mo-5V (VT22) alloy deformed by high pressure (cold and hot screw extrusion) are studied depending on its phase composition by the methods of X-ray diffraction analysis, optical microscopy, and electron microscopy. It is shown that the application of high pressure and complex schemes of deformation in combination with the action of temperature enables one to attain high levels of strains in the material without fracture. Under these conditions, new structures (containing nanosized particles responsible for the new properties) are formed. The mechanisms of deformation on the mesolevel are specified. It is shown that, in the process of cold hydroextrusion, the alloy in the one-phase β-state is deformed according to the mechanism of rotation via the formation of strain-induced martensite, whereas the alloy in the two-phase state is deformed according to the mechanism of bending. It is also shown that the mechanisms of deformation strongly depend on the initial phase composition of the alloy. The procedure of hot screw extrusion is characterized by the action of several mechanisms of deformation. Knowing these mechanisms, it is possible to choose the required modes of treatment and obtain structures guaranteeing the optimal combination of strength and plasticity. __________ Translated From Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 3, Pp. 57–64, May–June, 2006.     

DFT方法对LaNi5及LaNi5H0.5晶体结构的预测

根据密度泛函理论,以扩展平面波函数为基集,采用超软赝势技术,对LaNi5 储氢合金及其吸氢后的晶胞模型进行了优化,从理论上给出了其结构参数及性质。计算结果表明该方法能较好地符合 LaNi5 及其氢化物结构的实验值,为该类合金的结构预测提供了一个理论估算途径。此外,根据模型的结构参数分析了LaNi5 中不同间隙位的吸氢稳定性,解释了影响间隙位稳定性的因素。