Al—Li单晶体锯齿流变的动力学特征

研究了Ａｌ－Ｌｉ单晶体锯齿流变的动力学特征，结果表明：锯齿的频率和幅度与时效状态，变形和加载的晶体学位向相关，并与δ粒子被切割和固溶Ｌｉ原子对位错的钉扎有关。     

CRYOGENIC MECHANICAL PROPERTIES OF Al─Li SINGLE CRYSTAL

Ａｌ－Ｌｉ单晶体（７７Ｋ和２９３Ｋ）的塑性流变行为表明，Ａｌ－Ｌｉ单晶体的极限拉伸率度σｂ和最大均匀应变εｂ在低温下有所提高；形变硬化率ｄσ／ｄｅ和形变硬化指数ｎ的增加表明其均匀变形能力得以提高：Ａｌ－Ｌｉ中的锯齿流变（ＰＬＣ）效应与δ粒子和固溶Ｌｉ原子均有联系。     

热电池阳极Li-B合金放电前后的微观特征

使用扫描电子显微镜对放电前后的Ｌｉ－Ｂ合金的微观特征进行了观察，对影响Ｌｉ－Ｂ合金放电稳定性的主要因素进行了分析。结果表明，轧制后的Ｌｉ－Ｂ合金为塑性好的Ｌｉ包裹脆性的Ｌｉ７Ｂ６粒子，在５２０℃放电后Ｌｉ－Ｂ合金与电解质界面依然完整，在大电流（２００ｍＡ／ｃｍ＾２）短时间放充电后，金属锂被Ｌｉ２Ｂ６主电解质分割表现在断口上金属锂为细丝状。     

热电池及其阳极材料的研究与发展

叙述了热电池的发展过程，以及Ｃａ／ＣａＣｒＯ４和ＬｉＭｘ／ＦｅＳ２电池体系的电化学性能，着重介绍了ＬｉＭｘ／ＦｅＳ２热电池阳极材料的结构与电极性能，指出Ｌｉ－Ｂ合金是一种最有应用前景的阳极材料。     

Li3SiO4—Li3VO4混合导体中导电Li^＋离子对电子电导的作用

主要介绍了在不同测试电压下０．４Ｌｉ４ＳｉＯ４－０．６Ｌｉ３ＶＯ４混合导体电子电导率与温度关系的实验结果，提出了导电Ｌｉ＾＋离子对电子电导的作用机制，并由此解释了实验结果。     

熔融碳酸盐燃料电池隔膜用LiAlO2制备

将Ａｌ２Ｏ和Ｌｉ２ＯＣ３混合，６００－７００℃高温焙烧制备熔否则碳酸盐燃料电池囊和ＬｉＡｌＯ２粉体。工业生产Ａｌ２Ｏ３颗粒粒度和堆密度大，制得的ＬｉＡｌＯ２粉体较粗，有机金属化合物水解再脱水制备的Ａｌ２Ｏ３颗粒粒度和堆密度小，制备的ＬｉＡｌＯ２粉体细。     

V2O5薄膜电荷储存特性研究

本文采用真空蒸发制备了Ｖ２Ｏ５薄膜，用电化学方法从Ｌｉ离子电解质中向Ｖ２Ｏ５薄膜注入Ｌｉ离子。研究了Ｖ２Ｏ５薄膜中Ｌｉ离子储存特性、注入／退出可逆性以及电荷注入对其光学性能的影响。实验结果表明，Ｖ２Ｏ５薄膜具有较好的Ｌｉ离子储存特性和注入／退出可逆性，Ｌｉ离子的注入量受到膜中Ｖ＾５＋的含量及锂离子可占据的总位置数限制，而且离子注入Ｖ２Ｏ５薄膜的光学性能变化较小。     

Al-Li合金真空精炼与成分变化规律的研究

研究了Ａｌ－Ｌｉ合金真空除氢规律，并对比研究了真空除氢过程中化学成分变化规律，为Ａｌ－Ｌｉ合金的生产提供了重要参数，并为研究新一代高韧Ａｌ－Ｌｉ合金打下了基础。     

阴离子粘土LiAl2(OH)6X·2H2O(X=OH-,1/2CO32-)的离子交换特性

本文研究了阴离子粘土ＬｉＡｌ２（ＯＨ）６－Ｘ．２Ｈ２Ｏ（Ｘ＝ＯＨ＾－，１／２ＣＯ３＾２）的离子交换特性，结构分析表明，ＬｉＡｌ２－ＬＤＨ含水分隔层内的ＯＨ和ＣＯ３＾２－离子容易与酸性溶液中的Ｃｌ、ＮＯ３等离子进行交换，且保持ＬｉＡｌ２－ＬＤＨ的水滑石型层状结构不变，其中Ｃｌ－离子型表现较高的离子交换速率，在阴离子交换的同时，氢氧化以内的Ｌｉ＾＋离子也被Ｈ离子部分取代，但交换率较低，进一步讨论说明，     

Al－Li－Cu－Mg－Zr合金的晶界断裂

本文通过室温拉伸试验，利用扫描电镜和透射电镜研究了Ａｌ－Ｌｉ－Ｃｕ－Ｍｇ－Ｚｒ合金不同时效状态下的拉伸性能和断裂行为。结果表明，该合金的力学性能与主要强化相δ＇（Ａｌ３Ｌｉ）的尺寸有关，其断裂行为决定于位错的共面滑移程度和滑移与晶界沉淀相的交互作用。     

Quadratic Cohen representations in spectral analysis of serration process in Al–Mg alloys

Important from mechanical point of view the Portevin–Le Chatelier serration phenomenon is being characterized by a complicated spectral profile. As a typical example of nonstationary processes it demands a special treatment allowing to follow the evolution of energy of stress fluctuations as a function of strain. The authors suggest the utilization of a compact system of quadratic transformations, known as Cohen class, as a technique enabling the reliable analysis of serration processes. In this elaboration a comparison of the application of various Cohen decompositions to analyze frequency bands has been introduced.     

Effects of aging temperature and grain size on the formation of serrated grain boundaries in an AISI 316 stainless steel

The effects of aging temperature and grain size on the formation of serrated grain boundaries have been investigated in an AISI 316 stainless steel. Grain size increased slightly over aging temperature ranges of 650–870 °C, resulting in predominantly serrated grain boundaries. However, when the temperature exceeded 880 °C, the grain size significantly increased, and grain boundary serration was not observed. The initial grain size also had an influence on the occurrence of grain boundary serration. For specimen having a large initial grain size of about 200 μm, no serrated grain boundary formed after aging treatment at 760 °C. Serrated grain boundaries were observed when “normal” initial grain sizes 55 μm were employed. It was found that the frequency of low angle boundaries markedly increased as the initial grain size increased from 55 to 200 μm. From the results obtained, it is possible to describe that the grain boundary serration could be considered as a spontaneous reaction that aims to reduce the total free energy of the system, and form a new interface of lower free energy. We proposed that the competition between grain growth and grain boundary serration during aging treatment reduces the total free energy of the alloy system: at temperatures exceeding 880 °C, the dominant process is the grain growth, while grain boundary serration predominates over the range of 650–870 °C.     

Investigation of serrated flow behaviour in Al–10Mg alloy

Abstract

In view of reported anomalies in the serrated flow behaviour of aged Al–8.6Mg alloy, characteristics of serrated flow were investigated in an Al–10Mg alloy after solution treatment as well as after aging. The material was prepared by melting and casting, and then it was extruded, solution treated, and aged at either 150 or 200°C. Strain rate sensitivity, types of serration, onset strain of serrated flow, magnitude of serrations, and frequency of serrations were studied as a function of aging and strain rate. It was found that the alloy exhibited all the usual features of serrated flow except one, i.e. the magnitude of serration increased in the overaged condition after decreasing up to peak aging.     

Serration and noise behaviors in materials

Serration and noise behaviors in plastically deforming solids are related to avalanches of deformation processes. In the stress-strain curves, the serration characteristics are visible as stress drops or strain jumps. In fact, similar serration characteristics are ubiquitous in many structural and functional materials, such as amorphous materials [also metallic glasses, or bulk metallic glasses (BMGs)], high-entropy alloys (HEAs), superalloys, ordered intermetallics, shape-memory alloys (SMAs), electrochemical noise, carbon steels, twinning-induced plasticity steels (TWIP steels), phase-transformation-induced plasticity steels (TRIP steels), Al-Mg alloys, nano-materials, magnetic functional materials, and so on. Because of their unique and universal properties, many researchers have focused on this field to find out what causes the serration behaviors and what can be learned about the material from the serration characteristics. For example, the serration characteristics contain information about the mechanisms of plastic deformation and the structural evolution during deformation. However, due to many factors affecting the serration behavior and some uncertain or uncontrolled factors, it’s a difficult task to give a unified picture of a vast amount of serration data. This review article summarizes the results of previous studies in this rapidly-developing field, attempting to provide a new perspective in expounding the connection between macroscopic properties and micro-mechanisms.In this review paper, serration behavior of a wide range of materials will be discussed. One of the most important goals is to investigate the factors influencing serration characteristics and deformation mechanisms. Several statistical properties, such as distributions of stress drop sizes and waiting times, are reviewed and used to quantify the serration behavior. Moreover, models and theories on the serrated flow will be discussed, which quantify the deformation mechanism and provide physical intuition for the experiments, and methods to organize experimental data. Besides discussing serrations in stress-strain curves of many solid materials, this review paper will also cover other systems with serrations and collective noise, such as crackling noise in the earth’s crust (earthquakes), volume fluctuations in a granular medium and jamming behavior in random-packing systems.     

The study of work hardening in Fe-Mn-Al-C alloys

Three austenitic Fe-Mn-Al-C alloys with different aluminium content from 0, 5.1 and to 8.5wt% are chosen for the present work hardening study. Serrated stress-strain curves with pronounced work hardening were observed during tensile testing, also the serration of stress-strain curve is found to be decreasing as the increase of aluminium content. The serration can, however, still be observed even if the aluminium content is increased to as much as 8.5wt%. According to morphology studies and electron microscopic investigations, it is found that strain-induced deformation twins are closely related to the work hardening in the present alloys. Therefore, deformation twinning is strongly suggested as a major cause of work hardening in Fe-Mn-Al-C alloys, and also plays an important role on the serration of stress-strain curve.     

Texture effect on serrated flow in 2090 Al‐Li alloy

Tensile specimens of 1×6×25 mm in gauge dimension were cut from the surface and centre of 12.7 mm thick 2090 Al‐Li alloy plate, which were solution treated at 550 °C for 30 min, peak‐aged at 190 °C for 18 h, or reversion‐treated at 275 °C for 2 min. The flow stress of the centre layer was higher than that of the surface layer, regardless of the heat treatments. The textures of the surface and centre layers were approximated by the {001}<110> and {011}<211> orientations, respectively. The solution‐treated specimens gave rise to extensive serrations in their flow curves at a strain rate of 2×10^‐4 s^‐1. The serration amplitude was drastically reduced after the specimens were peak‐aged or reversion‐treated. However, for the peak‐aged alloy, the surface‐layer specimens underwent complex, serrated flows, whereas the flow curve of the centre‐layer specimen was almost devoid of serration. The serration, especially fine‐type serration in the peak‐aged and reversion‐treated specimens tended to disappear with increasing strain rate. The tensile behavior was explained in terms of the texture and strain rate.     

Improvement of creep-fatigue life by the modification of carbide characteristics through grain boundary serration in an AISI 304 stainless steel

The modification of carbide characteristics through grain boundary serration and its subsequent effect on the creep-fatigue property at 873 K have been investigated, using an AISI 304 stainless steel. It was found that the grain boundaries are considerably serrated when a specimen is furnace-cooled. The grain boundary serration leads to a change in the carbide characteristics as well as grain boundary configuration, i.e., morphology of carbide from an acute triangular to a planar form and a lowered density. Additionally, an array of carbide particles is changed from a consistent to zigzag pattern, in terms of their preference to one grain to share the coherency. Planar carbides on serrated grain boundaries have a lower interfacial energy than that of triangular carbides on straight grain boundaries. It is suggested that the modification of carbide characteristics through the grain boundary serration has a remarkable influence on the improvement of creep-fatigue resistance.Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, 373-1 Kusong-dong, Yusong-gu, Taejon 305-701, South Korea.     

A study on the mechanism of serrated grain boundary formation in an austenitic stainless steel

Measurement of the activation energy for the formation of serrated grain boundaries (GB) has been carried out to understand its underlying formation mechanism in an AISI 316 stainless steel. The apparent incubation time necessary to initiate grain boundary serration was obtained at different aging temperatures, and the apparent activation energy for serration was carefully calculated from the Arrhenius relationship between incubation time and aging temperature. The activation energy for GB serrations in this alloy was measured to be approximately 148 ± 20 kJ mole⁻¹, which is consistent with the activation energy for lattice diffusion of carbon in γ-iron (142 kJ mole⁻¹). This result indicates that GB serration could be controlled essentially by the lattice diffusion of carbon to grain boundaries. Based on the through-thickness observation of serrated GBs, a straight boundary began to serrate from the surface at an early stage of the aging treatment, and then the serrated parts propagated throughout the entire grain boundary.     

EFFECT OF FACTOR OF BLUE BRITTLE OF LOW-CARBON STEEL FOR TENSILE DEFORMATION

本文研究了形变温度、形变速率及材料晶粒度等因素对10~零钢拉伸形变时蓝脆现象的影响。结果表明,温度改变着PL 效应区的锯齿波型,晶粒尺寸增加和高的拉伸形变速率可提高PL 效应区的起始温度T(?)及终止温度T(?),改变材料出现蓝脆现象的温度及其范围。位错结构变化证实,在PL效应区内,溶质原子对运动位错的钉扎存在着由弱至强的转化过程。