CuSn合金熔体结构转变及其动力学行为探索

迄今为止,人们对合金在液相线之上的熔体结构转变过程的认识仍不清晰. 本文运用电阻法、DSC热分析等实验手段,对CuSn60wt%二元合金熔体在升温及保温条件下的结构转变动力学过程进行了研究,并通过相变动力学理论探讨了转变过程的特征与微观物理机制. 分析表明：合金熔体中温度诱导的结构转变过程符合“形核-长大”类型,其动力学过程为自动催化转变模式,其中液相中新结构原子团簇的“形核率”为转变速率的主导控制因素.     

CuSn合金熔体结构转变及其动力学行为探索

迄今为止,人们对合金在液相线之上的熔体结构转变过程的认识仍不清晰. 本文运用电阻法、DSC热分析等实验手段,对CuSn60wt%二元合金熔体在升温及保温条件下的结构转变动力学过程进行了研究,并通过相变动力学理论探讨了转变过程的特征与微观物理机制. 分析表明：合金熔体中温度诱导的结构转变过程符合“形核-长大”类型,其动力学过程为自动催化转变模式,其中液相中新结构原子团簇的“形核率”为转变速率的主导控制因素.     

以内耗技术探索Pb-Sn合金熔体的结构变化

以改进的低频扭摆内耗仪研究了液态PbSn合金连续升温过程的内耗行为.结果表明:合金在液相线以上500—800℃温区内出现内耗峰,其峰温不随频率变化,峰高与升温速率成正比,与振动频率成反比,这与固态相变内耗峰的特征相吻合;合金成分不同,内耗峰峰温不同;非共晶成分合金熔体的内耗曲线上出现次峰.这一现象揭示了PbSn合金熔体随温度可能发生结构转变.对PbSn合金进行差热分析,熔体出现的热效应峰与内耗峰的温区大体对应,进一步揭示熔体的内耗峰可能是由结构转变引起的. 关键词： 液态结构 内耗 Pb-Sn合金     

电磁感应式液固态金属电阻率定性测量装置及应用

介绍了一种自主研制的非接触式电阻率测量装置,该装置基于电磁感应原理,可实现降温过程中金属从液态到固态各阶段电阻率的定性测量,为实时表征金属材料的结构变化提供了一种有效的测量工具.详细介绍了该装置的设计原理及其结构,同时利用该装置,测量了金属Zn,Sb以及过共晶Zn-70 wt.% Sb合金降温过程中电阻率随温度的变化情况,验证了该装置的可靠性. 关键词： 电阻率 电磁感应 液态金属 结构转变     

Mg-Al合金熔体中固液界面结构的分子动力学研究

本文采用分子动力学研究了Mg-3%Al合金熔体中固液界面结构及界面附近原子的扩散行为.计算结果表明,该二元合金的固液界面为粗糙界面.垂直于界面方向的数密度分布,表现出复杂波动的特征,这种波动一直延伸到液体中.在界面附近的区域,扩散系数的三个不同方向的分量表现出了明显的各向异性,并且这种各向异性一直持续到液相当中.对界面二维结构的分析表明,界面附近液相原子的二维排列呈现出从长程有序逐渐过渡到短程有序的变化.     

Pb-Sn合金固—液转变过程的内耗行为

在连续升温过程中,测量了Pb-Sn合金的内耗.实验发现：在共晶成分范围内,伴随着Pb-Sn 合金的固—液转变,内耗值出现突然下降.内耗值的下降幅度与Pb-Sn合金成分有关.固—液 转变过程中的内耗是由材料结构变化或弛豫时间变化引起的. 关键词： 内耗 固—液转变 Pb-Sn合金     

液态金属急冷过程中微观结构转变的研究

本文对液态金属Ａｌ在溶态及急冷过程中的微观结构及其转变进行了分子动力学模拟研究。发现在由ＨＡ（Ｈｏｎｅｙｃｕｔ－Ａｎｄｅｒｓｅｎ）健型指数所确定的双锥体原子团结构的数目随急冷温度变化的关系曲线上存在着二个明显的转变点。第一个点与熟知的玻璃转变温度Ｔｇ相吻合；而第二个点则为新发现的低温端相交点Ｔｇ２。这一结果为用分子动力学方法从微观层次上研究结构相变过程提供了一条新途径。     

液态In-80wt%Sn合金结构的分形分析

在X射线衍射实验的基础上，把分形理论用于分析In-80wt%Sn在300℃时的液态结构，发现液态结构是一种多度域分形结构，并提出液态结构多度域分形模型.通过分形分析，液态合金的整体结构被清晰地呈现出来.推测多度域两分形之间过渡区的大小和液态合金性质有关，过渡区的变化可能反映了液态合金性质的变化. 关键词： 液态合金结构 分形理论 多度域分形     

高温合金熔体密度的教学过程设计

密度是十分基本且非常重要的物理量,但密度十分常见,因此在高温合金熔体性质教学和学习过程中,常常重视不够,以致影响对高温熔体性质的认识。本文根据高温合金熔体的基本物理化学性质,创新教学方法,精心进行教学过程设计,首先以航空发动机用Inconel718合金的固态和液态密度随温度的变化作为切入点,抓住学生的学习兴趣点,进而“有设计”“有构思”地引出密度测定为什么难、如何进行实验测定、典型的密度变化规律等体系化的知识。这一教学过程设计生动形象地讲授了高温合金熔体密度的课堂内容,深化了液态金属结构与性质的教学效果。     

液态金属高温结构转变特性的模拟研究

对液态金属Al的高温结构转变特性进行了分子动力学模拟研究,获得各种键型原子组态变化的重要结果.并利用Honeycutt-Anderson键型指数所定义的小原子团类型与一定的有序度相对应的观点,对模拟结果及其在选择恰当的材料凝固起始温度中的重要指导作用,进行了相应的讨论. 关键词：     

Spatial heterogeneity in liquid–liquid phase transition

Molecular dynamics simulations are performed to investigate the liquid–liquid phase transition(LLPT) and the spatial heterogeneity in Al–Pb monotectic alloys. The results reveal that homogeneous liquid Al–Pb alloy undergoes an LLPT,separating into Al-rich and Pb-rich domains, which is quite different from the isocompositional liquid water with a transition between low-density liquid(LDL) and high-density liquid(HDL). With spatial heterogeneity becoming large, LLPT takes place correspondingly. The relationship between the cooling rate, relaxation temperature and percentage of Al and the spatial heterogeneity is also reported. This study may throw light on the relationship between the structure heterogeneity and LLPT, which provides novel strategies to control the microstructures in the fabrication of the material with high performance.     

偏晶合金液-液相分离的格子玻尔兹曼方法模拟

本文建立了一个模拟在弥散相液滴的扩散长大、碰撞凝并和Ostwald熟化等因素的作用下偏晶合金液-液相分离过程的二维格子玻尔兹曼方法 (lattice Boltzmann method, LBM) 模型.该模型结合了Shan-Chen的两相流模型和Qin的介观粒子相互作用势模型的优点,并在LB演化方程中引入了反映相变的源项.应用该模型模拟研究了偏晶合金液-液相分离过程中单液滴的生长、两液滴的合并和多液滴的生长规律.结果表明在两液相区中第二相单个液滴的生长是一个通过扩散从非平衡态到平衡态过渡的过程.两液滴合并 关键词： 偏晶合金 液-液相分离 格子玻尔兹曼方法     

Layering of confined water between two graphene sheets and its liquid-liquid transition

Molecular dynamics(MD) simulations are performed to explore the layering structure and liquid–liquid transition of liquid water confined between two graphene sheets with a varied distance at different pressures. Both the size of nanoslit and pressure could cause the layering and liquid–liquid transition of the confined water. With increase of pressure and the nanoslit's size, the confined water could have a more obvious layering. In addition, the neighboring water molecules firstly form chain structure, then will transform into square structure, and finally become triangle with increase of pressure. These results throw light on layering and liquid–liquid transition of water confined between two graphene sheets.     

The Boson peak in confined water: An experimental investigation of the liquid-liquid phase transition hypothesis

The Boson peak (BP) of deeply cooled confined water is studied by using inelastic neutron scattering (INS) in a large interval of the (P, T) phase plane. By taking into account the different behavior of such a collective vibrational mode in both strong and fragile glasses as well as in glass-forming materials, we were able to determine the Widom line that characterizes supercooled bulk water within the frame of the liquid-liquid phase transition (LLPT) hypothesis. The peak frequency and width of the BP correlated with the water polymorphism of the LLPT scenario, allowing us to distinguish the “low-density liquid” (LDL) and “high-density liquid” (HDL) phases in deeply cooled bulk water.Moreover, the BP properties afford a further confirmation of theWidom line temperature T_W as the (P, T) locus in which the local structure of water transforms from a predominately LDL form to a predominately HDL form.     

Liquid-liquid phase transition in water

Water shows anomalies different from most of other materials.Different sceniaros have been proposed to explain water anomalies,among which the liquid-liquid phase transition(LLPT)is the most discussed one.It attributes water anomalies to the existence of a hypothesized liquid-liquid critical point(LLCP)buried deep in the supercooled region.We briefly review the recent experimental and theoretical progresses on the study of the LLPT in water.These studies include the discussion on the existence of the first order LLPT in supercooled water and the detection of liquid-liquid critical point.Simulational results of different water models for LLPT and the experimental evidence in confined water are also discussed.     

快速凝固Cu-Pb过偏晶合金的性能表征

研究了Cu-Pb过偏晶合金的急冷快速凝固组织特征,定量表征了快速凝固Cu-Pb过偏晶合金的电阻率和力学性能,理论分析了冷却速率和组织形态对合金性能的影响规律. 研究结果表明,在急冷快速凝固条件下,Cu-Pb过偏晶合金中的(Cu)相和(Pb)相均以枝晶方式生长,晶体形态以均匀细小的等轴晶为特征. 随着冷却速率增大,一方面,凝固组织显著细化,晶界增多,对自由电子的散射作用增强,合金电阻率显著增大;另一方面,细晶强化作用增强,合金的抗拉强度呈线性升高,同时,伴随着晶体缺陷数量的增多,合金的伸长率降低. 关键词： Cu-Pb过偏晶合金 快速凝固 电阻率 力学性能     

快速凝固Cu-Sn亚包晶合金的电阻率及力学性能

定量表征了快速凝固Cu-xwt%Sn(x=7, 13.5, 20)亚包晶合金的电阻率和力学性能，理论分析了冷却速率与合金性能之间的关系. 研究结果表明，在急冷快速凝固条件下，随着冷却速率的增大，合金组织显著细化、晶界增多，对自由电子的散射作用增强，Cu-Sn亚包晶合金的电阻率升高. 当晶界散射系数取r=0.992时，可用M-S模型分析其电阻率.同时，细晶强化作用增强，合金的显微硬度和抗拉强度呈线性增大，并且细晶区显微硬度略大于粗晶区显微硬度. 冷却速率的增大使合金的伸长率减小，其值在1.0%—4.6%范围.     

哈斯勒合金Ni-Mn-Sn的马氏体相变与反磁热性质

通过结构以及磁性测量,研究了哈斯勒合金Ni₅₀Mn_25+xSn_25-x (x=11,12)的马氏体相变和磁热性质.结果表明,与样品在奥氏体相的磁性不同,由于在马氏体相中反铁磁交换作用的增强,导致铁磁和反铁磁在马氏体状态下共存.此外,通过Maxwell方程,研究了两样品在不同磁场变化下马氏体相变温度附近的反磁热性质,并阐明了该系列合金产生大的正磁熵变(ΔS_M)不仅与其在降温过程中发生马氏体相变所导致的磁跃变(ΔM)有关,而且与发生马氏体相变所经历的温度区间有密切的联系. 关键词： 哈斯勒合金 Ni-Mn-Sn 马氏体相变 正磁熵变     

Magnetostructural transition in NiCuCoMnGa alloys

The effects of the addition of Co on the martensitic transformation and Curie transition temperatures of polycrystalline Ni46-xCu4CoxMn33.sGa16.5 （x = 0, 1, 3, 5） alloys are investigated. An abrupt decrease in the martensitic transformation temperature and an obvious increase in the Curie transition temperature of austenite （TA） are observed when Co is doped in the NiCuMnGa alloy. As a result, the composition range for obtaining the magnetostructural transition is extended. Furthermore, the effect of a strong magnetic field on the magnetostructural transition is analyzed. This study offers a possible method to extend the composition range for obtaining magnetostructural transition in Heusler alloys.     

Spin treatment-based approach for electronic transport in paramagnetic liquid transition metals

A novel concept is proposed to calculate both the electrical resistivity and thermoelectric power (TEP) of liquid transition metals (Mn, Fe, Co and Ni) characterized by a paramagnetic state in the liquid phase. By contrast to a previous work (PRB64, 094202 (2001)), where the resistivity was calculated by treating separately the interactions between spin up and spin down using the Matthiessen rule, our current approach is based on two types of muffin tin potentials in the t-matrix, namely spin up and spin down. The resistivity is treated as the result of the interference of the two kinds of spin states of electrons including a cross-contribution. The calculated resistivity values agree reasonably well with the available experimental ones for all the metals considered. Moreover, the calculated TEP, as deduced from the slope of resistivity vs. energy, has been found to be positive for Mn and Fe but negative for Co and Ni. Besides that, this formalism for resistivity calculation may be generalized to a system that may exist in different atomic states. It is worth mentioning that this concept is analogous to the one used in the process of neutron scattering on a metal composed of multiple isotopes.