The growth kinetics of intermetallic layers at the interface of a solid metal and a liquid solder

During soldering, intermetallic layers can occur at the interface of a solid metal and the saturated or undersaturated solder melt. In systems with a considerable solubility in the liquid state, dissolution causes a manifold drop in layer thickness. Mathematical equations are proposed to evaluate the thickness of any intermetallic layer formed under conditions of simultaneous dissolution in the undersaturated solder melt. The main features of reactive phase formation at the solid metalliquid solder interface are illustrated using the Co-Sn couple with the growing CoSn₃ (250°C) and CoSn₂ (350°C and 450°C) layers as examples.     

Crystallography of Fe2Al5 phase at the interface between solid Fe and liquid Al

In this study, the microstructures and crystallographic features of a η-Fe₂Al₅ phase formed on pure Fe hot-dipped in a pure Al melt at 750 °C were examined in order to understand the η phase layer formation having a saw-tooth morphology. A number of the columnar η grains (forming the η phase layer) grow towards the solid Fe (α-Fe) side along the [001] direction, resulting in a significant saw-tooth morphology at the interface between the η and α-Fe phases. The neighboring η grains have high-angle boundaries with a common [001] axis. In the η phase layer, the low-angle boundaries develop close to the liquid Al side, and their density becomes higher with longer dipping times, resulting in the development of a fine dislocation substructure in the η phase. In the α-Fe phase, fine substructure consisting of a high density of low-angle boundaries develops around the growth tips of the columnar η grains. These substructure developments are likely responsible for the α → η transformation strain. A possible mechanism for the formation of this η phase layer having a saw-tooth morphology will be discussed in terms of the stress field caused by the α → η transformation.     

Sn-9Zn-0.1S/Cu焊点液固界面金属间化合物的生长动力学

采用扫描电镜和光学显微镜观察研究了230~260℃焊接温度范围内Sn-9Zn-0.1S/Cu焊点界面金属间化合物的结构及生长动力学.结果表明,在该焊点界面形成的化合物可分为两层:靠铜侧的是厚且平直的γ-Cu₅Zn₈化合物层;靠焊料侧的则为另一薄且呈扇贝、粒状的CuZn化合物层.提高钎焊温度及延长反应时间基本不改变Sn-9Zn-0.1S/Cu焊点界面金属间化合物的结构和成分,但会使形成的界面金属间化合物层厚度增加.γ-Cu₅Zn₈金属间化合物层的厚度与反应时间的平方根呈线性关系,表明其生长由扩散机制控制.根据阿伦尼乌斯公式,Sn-9Zn-0.1S/Cu焊点界面γ-Cu₅Zn₈金属间化合物层反应活化能为22.09 kJ/mol.     

Relationship between solid/liquid interface and crystal orientation for pure magnesium solidified in fashion of cellular crystal

The relationship between the solid/liquid interface and the crystal orientation for pure magnesium,which grows in fashion of cellular crystal in unidirectional solidification,was investigated.The results show that the energy of the solid/liquid interface is the lowest during cellular crystal growth of pure magnesium;and the solid/liquid interface is covered by the basal face{0001}and by the crystal face made up of three atoms located at the orientation{0001}<0100>and two atoms located at the inner of magnes...     

非晶合金的晶化动力学与初生相的内在联系

通过差示扫描量热法(DSC)研究了Zr60Al15Ni25非晶合金的晶化动力学。X射线衍射(XRD)和能谱(EDS)分析结果表明:Zr60Al15Ni25非晶合金晶化过程中的初生相为复杂三元化合物Al2NiZr6和AlNi4Zr5。非晶合金的有效晶化激活能反映了晶化初生相与非晶相间的结构差异,二者结构差异越大,有效晶化激活能就越高,Zr60Al15Ni25非晶合金的有效晶化激活能高达345 kJ/mol;当合金高温熔体快冷过程中的初生相与非晶合金的晶化初生相一致时,晶化动力学参数能够实际反映合金的玻璃形成能力,相反则不能。     

Equilibrium shape and interface roughening of small liquid Pb inclusions in solid Al

The shape of liquid Pb inclusions embedded in a solid Al matrix was investigated at temperatures between 300 and 500°C using in-situ electron microscopy. Inclusion shapes in the size range from a few nanometers to about 150 nm were found to depend on size, temperature and thermal history. During isothermal annealing after melting, small inclusions rounded off while larger inclusions remained faceted until the temperature was raised to about 500°C. During subsequent cooling, inclusions refaceted, although less strongly than during heating. The shape hysteresis between heating and cooling cycles was found to be due to the barrier of ledge nucleation necessary to advance the faceted interfaces. It is shown that this kinetic barrier can explain the observed dependence on size and temperature, and that the {1 1 1} interface undergoes a roughening transition at about 550°C. Even under conditions of kinetic limitation it was possible to measure local equilibrium by modeling kinetically limited inclusions as a droplet in a crevice. For this type of measurement, the hysteresis between heating and cooling cycles disappeared, and the true equilibrium shape could be derived. The anisotropy of interfacial energy was shown to be significantly smaller than previously reported, and at about 2%, similar to the anisotropy of the surface energy for fcc metals. From the width of facets on the equilibrium shape, the step energy was determined to be =1.9·10⁻¹¹ J/m at 350°C.     

Role of the solid/liquid interface faceting in rapid penetration of a liquid phase along grain boundaries

A model is developed for describing rapid penetration of a liquid phase along a grain boundary. It is based on the assumption of a highly faceted solid/liquid interface. Experiments showing the faceting of the solid/liquid interface in grain boundary penetration experiments are presented. The basic hypothesis of the model are an undersaturated solid and a positive spreading coefficient of the liquid phase along the grain boundary. The model explains the apparent concave shape of the tip of the groove and the reason why penetration also occurs if the liquid phase is pre-saturated with the material of the solid. Moreover it predicts a power law with an exponent close to unity for the time dependence of the depth of penetration of the liquid layer along the grain boundary.     

Determination of thermal conductivities of solid and liquid phases for rich-Sn compositions of Sn-Mg alloy

The variations of thermal conductivities of solid phases versus temperature for pure Sn and Sn-1 wt% Mg, Sn-2 wt% Mg, and Sn-6 wt% Mg binary alloys were measured with a radial heat flow apparatus. Thermal conductivity variations versus temperature for pure Sn and Sn-1 wt% Mg, Sn-2 wt% Mg, and Sn-6 wt% Mg binary alloys were found to be 60.60 ± 3.63, 61.99 ± 3.71, 68.29 ± 4.09, and 82.04 ± 4.92 W/Km, respectively. The thermal conductivity ratios of liquid phase to solid phase for pure Sn and eutectic Sn-2 wt% Mg alloy at their melting temperature were found to be 1.11 and 1.08, respectively, with a Bridgman type directional solidification apparatus. Thus the thermal conductivities of liquid phases for pure Sn and eutectic Sn-2 wt% Mg binary alloy at their melting temperature were evaluated to be 67.26 ± 4.03 and 73.75 ± 4.42 W/Km, respectively, by using the values of solid phase thermal conductivities and the thermal conductivity ratios of the liquid phase to the solid phase.     

Morphological observations of the reaction between liquid Sn and solid Pb

The morphology of the reaction between solid Pb and liquid Sn was studied at 250° and 300°C. Metallographic examination of the solidified sample indicated the existence of five distinct morphological zones. The existence of each zone is rationalized using the phase diagram. A simple SnPb eutectic zone was found at the original solid Pb-liquid Sn interface. The thickness of this zone was found to increase linearly with time. This linear growth was attributed to the constant rate of dissolution of the Pb phase.     

Structural transformations upon the mechanochemical interaction between solid and liquid metals

The process of mechanochemical interaction of solid and liquid metals is examined. It is shown that the mechanochemical formation of solid solutions in all the cases occurs through the stages of the formation of stable intermetallic compounds.     

氟化钾对固态铝电解质物相的影响

本文用X-射线衍射法研究了KF与冰晶石的反应及其对固态铝电解质物相的影响。研究表明:KF与Na3AlF6(冰晶石)在熔盐中能够发生化学反应,无论是在酸性还是碱性电解质中产物都有K2NaAlF6(钾冰晶石),但在酸性电解质中其反应产物同时有K2NaAl3F12和K2NaAlF6两种物相。随着KF含量的增加以及电解质酸度的增强,K2NaAl3F12的含量增加。本文还提出了K2NaAl3F12物质的生成机理以及对同时含CaF2、LiF、MgF2和KF的铝电解质的物相进行了鉴定。对分子比定义为碱性氟化物与AlF3的摩尔比进行了验证,表明只有这种定义才能够真正体现电解质的酸碱性。     

Phase transformation studies at the solid/liquid interface by directional solidification of Alloy 718

The phase transformation temperatures are especially important in alloy 718 because it requires careful heattreatment cycles. The DTA method is generally used to estimate the characteristic temperatures of phase transformations. However, DTA is an indirect method to confirm phase transformations, and there are always discrepancies in analyzing the DTA thermograms. In this study, the directional solidification and quenching technique has been applied to estimate the phase transformation temperatures near the solid/liquid interface temperatures by measuring temperatures directly during directional solidification. These phase transformation temperatures were confirmed in the quenched solid/liquid interface. Solidification behavior at the solid/liquid interface with solidification rate and temperature gradient were also discussed.     

Measurements of the interface between 5083 aluminium and liquid mercury using impedance spectroscopy

In natural gas processing plants, the aluminium oxide passive layer has been postulated to protect the underlying aluminium from mercury embrittlement. Under certain circumstances the oxide film may break down, leading to catastrophic failure. In this study, impedance techniques are used to investigate the interface between Al-5083 and liquid mercury at room temperature. The effects of aging time, aging atmosphere and mercury exposure time on the interface were studied and are discussed in terms of the nature of the film. The implications of this work on the integrity of aluminium gas processing equipment exposed to mercury are examined.     

Processes at the liquid/crystal boundary upon contact melting in the system with intermediate solid phases

Growth of the liquid interlayer in the indium-tin system at 400 K in the process of contact melting in the nonstationary diffusion regime has been investigated experimentally. The contact pairs were composed of pure substances, solid solutions, and intermediate solid phases. The previously developed concepts have been extended to include the case where the existence of intermediate solid phases on both sides of the liquid phase should be taken into account. It follows from the results obtained that the concentration range of the liquid interlayer corresponds to the homogeneity range of the liquid phase in the phase diagram at the temperature of experiments. The results of the experiments can be explained based on the model according to which solid solutions and intermediate solid phases at the liquid/crystal interface arise due to the precipitation from the metastable melt supersaturated by the substance of the adjacent phase.     

The material optimization and reliability characterization of an indium-solder thermal interface material for CPU packaging

Developing new thermal interface materials (TIMs) is a key activity to meeting package thermal performance requirements for future generations of microprocessors. Indium solder is capable of demonstrating end-of-line performance to meet current technology targets due to its inherent high thermal conductivity. However, improving its reliability performance, particularly in temperature cycling, is a challenge. This study describes the failure mechanisms and reliability performance of indium solder TIM as a function of integrated heat spreader metallization thickness, TIM bond line thickness, and die size. Also studeited were the steps taken to improve its temperature cycle performance. Analyses were performed using thermal resistance measurements, scanning-electron microscopy, scanning-acoustic microscopy, and transmission-electron microscopy to characterize the solder TIM thermal performance, interfacial microstructure, and failure mechanisms.     

The impact of stochastic atomic jumps on the kinetics of curvature-driven grain growth

A model for grain growth allowing stochastic jumps of atoms across boundaries to occur concurrently with curvature-driven boundary migration has been solved numerically. At small grain sizes, the stochastic mechanism controls the overall rate of grain growth, whereas at large sizes, the growth rate is governed by the boundary curvature. The transition between the two regimes occurs smoothly over a range of grain sizes about one order of magnitude in width. Since the upper bound of the transition range is estimated to lie below 20 nm for most polycrystalline materials, the stochastic mechanism is expected to be relevant to the measurement and modeling of grain growth only in nanocrystalline samples.     

镀铝温度对渗铝层/基体界面空洞生长动力学的影响

采用不同的镀铝温度在20碳钢上制备了不同厚度的热浸镀铝层,通过测量热浸镀铝层厚度以及高温氧化后渗铝层/基体界面空洞平均直径和形核数量随氧化时间的变化,研究了镀铝温度对渗铝层/基体界面空洞生长的影响。结果表明:随镀铝温度升高,镀铝后的表面层厚度减小,合金层厚度增加;在高温氧化期间,渗铝层/基体界面空洞的生长速度随镀铝温度的升高而减小,其变化规律与热浸镀铝后表面层厚度随镀铝温度的变化规律相一致;界面空洞平均深度随镀铝温度升高而增加,其变化规律与热浸镀铝后合金层厚度随镀铝温度的变化规律相一致;界面空洞增量随氧化时间的延长先增加而后逐步减少,且镀铝温度越高,空洞形核速度越小。分析了镀铝温度对界面空洞生长的影响机制。     

The effect of atomic hydrogen on the kinetics of iron passivation in neutral solutions

Current-time dependences are recorded on iron in borate buffer (pH 7.4 and 6.7) and its mixture with NS4 solution (pH 6.7) at the potentials of passivity, active-passive transition, and prepassivation of iron. Hydrogenation of the metal is found to accelerate the dissolution of iron in steady passive state, produce no effect on the growth of a barrier layer, and prevent the formation of a primary passivating film. Atomic hydrogen decelerates the active dissolution of iron, which determines the anodic current at the initial stage of the metal passivation.