Diffusion induced isothermal solidification during transient liquid phase bonding of cast IN718 superalloy

In transient liquid phase (TLP) bonding for commercial applications, one of the important key parameters is the holding time required for complete isothermal solidification t_IS, which is a prerequisite for obtaining a proper bond microstructure. The objective of the study is to analyse the isothermal solidification kinetics during TLP bonding of cast IN718 nickel based superalloy. Experiments for TLP bonding were carried out using a Ni–7Cr–4·5Si–3Fe–3·2B (wt-%) amorphous interlayer at several bonding temperatures (1273–1373 K). The time required to obtain TLP joints free from centreline eutectic microconstituents was experimentally determined. Considering the solidification behaviour of residual liquid, t_IS could be predicted by a mathematical solution of the time dependent diffusion equation based on Fick’s second law.

Dans la brasure en phase liquide transitoire (TLP) pour applications commerciales, l’un des paramètres clés importants est le temps de maintien requis pour la solidification isotherme complète (t_IS), qui est une condition requise pour l’obtention d’une microstructure adéquate du lien. L’objectif de cette étude est d’analyser la cinétique de la solidification isotherme lors de la brasure TLP du superalliage coulé à base de nickel, IN718. On a effectué les expériences de brasage de TLP en utilisant une couche de liaison amorphe de Ni–7Cr–4·5Si–3Fe–3·2B (% en poids) à plusieurs températures de brasage (1273–1373 K). On a déterminé expérimentalement le temps requis pour l’obtention de joints TLP libres de micro constituants eutectiques à la ligne centrale. En considérant le comportement de solidification du liquide résiduel, on pouvait prédire t_IS au moyen d’une solution mathématique de l’équation de diffusion dépendante du temps basée sur la seconde loi de Fick.     

Kinetic study of low-temperature transient liquid phase joining of an aluminum-sic composite

The transient liquid phase (TLP) joining of an aluminum 6061-SiC composite using a gallium interface has been investigated. The observed kinetics of this process suggest that diffusion occurs along interphase and subgrain boundaries at low temperatures (<723 K). An existing TLP model has been modified to account for this behavior.     

Microstructural study of transient liquid phase bonded cast INCONEL 738LC superalloy

The microstructure of the transient liquid phase (TLP) bonded joint of a cast INCONEL 738LC superalloy, made with a commercial Ni-Cr-B filler alloy, Nicrobraz 150, was examined by analytical scanning and transmission electron microscopic techniques. Due to incomplete isothermal solidification at the bonding temperature, the residual liquid interlayer transformed to nonequilibrium eutectic microconstituents consisting of chromium-rich M₅B₃, nickel-rich M₂₃B₆, and nickel-based γ solid solution phases. Also, a significant volume fraction of complex fcc Cr-Mo-W rich carboborides was observed in the joint/base alloy interface region. This is contrary to the predictions of the currently available TLP models that predict a precipitate-free joint/base alloy interface. It is suggested that solid-state diffusion of boron prior to completion of equilibration process induced the formation of carbo-boride phase, which needs to be adequately considered to develop an optimum postbraze heattreatment process to produce a joint with optimum properties.     

A study of transient liquid-phase bonding of Ag-Cu using differential scanning calorimetry

A novel approach using differential scanning calorimetry (DSC) to quantify interface kinetics in a solid/liquid diffusion couple is applied to characterize the isothermal solidification stage during transient liquid-phase (TLP) bonding of Ag and Cu using a Ag-Cu interlayer. When the DSC results are properly interpreted, the measured interface kinetics are more accurate than those obtained using traditional metallographic techniques. Experimental results are compared to predictions for isothermal solidification given by a selection of analytical models. The comparison yields close agreement with a solution that assumes a moving boundary; but accuracy of the predictions is very sensitive to selection of solute diffusivity. Metallographic inspection of the DSC samples and traditional TLP bonds validates the kinetics measured using this technique, and supports the prediction given by the analytical model. This study shows that the method of using DSC to quantify interface kinetics is valuable in the refinement of process parameters for TLP bonding. Furthermore, simple analytical solutions can be applied to predict the process kinetics of isothermal solidification in simple binary systems with considerable accuracy when the effects of grain boundaries can be neglected, thus reducing the need for complex numerical models when developing process parameters.     

Fe基多孔材料瞬时液相烧结过程研究

采用定量DSC差热分析、扫描电镜分析、背散射元素分析以及XRD物相分析等方法对添加Ni-P共晶合金的Fe粉瞬时液相烧结过程进行了研究.研究发现,粉末颗粒粒度、烧结时间等参数对烧结过程有重要的影响.粉末粒度较小时,烧结升温过程中元素间的固相扩散比较明显,但粉末粒度对形成液相的总量影响较小.液相烧结时,固相Fe元素向液相中...     

Experimental study of the kinetics of transient liquid phase solidification reaction in electroplated gold-tin layers on copper

The kinetics of transient liquid phase (TLP) solidification in Au-Sn layers electroplated on Cu foil was investigated using differential scanning calorimetry (DSC). The solidification reaction takes place between a eutectic liquid of melting point 280 °C, which is shown to form in preference to other compositions, and an excess gold-rich layer. The solidification kinetics and the amount of melt formed were measured as a function of foil aging time. It is shown that the well-documented rapid interdiffusion at low temperatures between gold and tin can account for a decrease in the amount of melt produced during heating with age time. An estimate of the effective diffusivity of tin into gold at 295 °C has been obtained from measured solidification rates. The effect of copper diffusing through the gold film on the solidification kinetics was also investigated.     

Investigations of the bonding mechanism at the joining region of a steel sandwich sheet

A steel sandwich sheet was produced by a high temperature dipping process. An unalloyed steel was used as substrate and an alloyed steel as coating. At the interface of the sandwich sheet a good bonding between the two different steels could be achieved by a bonding process, which was caused by the formation of a diffusion induced liquid phase. Since the bonding is connected to the formation of the liquid phase at the interface, this is similar to a conventional welding process. This welding process was investigated at the interface of well and partially bonded specimens. Based on these investigations the bonding mechanism could be explained.     

Sequential analysis applied to counseling process and outcome: A case study revisited.

A case study presented by C. E. Hill et al (see record 1983-10832-001) was analyzed further with sequential analysis methods developed by B. E. Wampold (see PA, Vol 71:30503; in press) and Wampold and G. Margolin (see record 1983-04841-001) to demonstrate the usefulness of these methods for understanding counseling process and outcome. Several interactive patterns were investigated including unidirectional independence, bidirectional independence, and dominance. Process was linked to outcome by examining the relations of various interactive patterns and satisfaction with and evaluation of each session as rated by the client, the counselor, and observers. The present sequential analysis revealed several facets of the interaction between the counselor and the client that were undetected by Hill et al.'s analysis. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Thermal analysis of the compositional shift in a transient liquid phase during sintering of a ternary Cu-Sn-Bi powder mixture

In this work, differential scanning calorimetry (DSC) and microstructural analysis were used to study the transient-liquid-phase sintering (TLPS) of a Cu-Sn-Bi powder mixture. During sintering, the liquid phase shifts from a Sn-rich (i.e., ∼90 wt pct Sn) to a Bi-rich (i.e., >78 wt pct Bi) composition. In addition, the presence of Bi creates two melting events: a Sn:Bi eutectic reaction at 139 °C and a reaction involving the melting of (Bi) at 191 °C. The Sn:Bi eutectic melting event was fully transient. The melting event at 191 °C was consistent with the formation of a terminal Bi-rich liquid phase. The rate of compositional shift toward this terminal liquid phase at 260 °C was dependent on the rate of the reaction of the Sn with the Cu powder to form intermetallic phases. For mixtures made with medium and fine Cu powder, the terminal Bi-rich composition was reached after isothermal hold times of 20 and 15 minutes, respectively. This resulted in a new melting point for the mixture of 191 °C. For coarse Cu powders, the rate of the compositional shift toward a Bi-rich composition was much slower. The liquid phase remained at a hypoeutectic Sn-Bi composition estimated at 80 wt pct Sn, while the mixture maintained a melting point of 139 °C.     

Tensile behavior of carbon nano-fiber-reinforced Cu composite using the liquid infiltration process

A carbon nano-fiber (CNF)-reinforced Cu composite was fabricated by the liquid infiltration process, and the tensile behavior of the fabricated composite was evaluated. For the unidirectional alignment of the severely entangled CNFs, the mechanical drawing process was utilized. The bundle of drawn Cu tubes, compacted with unidirectionally aligned CNFs, was placed on the specially designed mold. The mold was subsequently canned, degassed, evacuated, heated at 1100 °C for 10 minutes in the electric furnace to liquefy the Cu, and, finally, transferred to the press. The optical and scanning electron microscope (SEM) micrographic observations of the final product demonstrated that, even though the CNFs were not uniformly distributed throughout the specimen due to the molten metal flow during the melting process, the local unidirectionality was preserved in those areas where CNFs were densely packed. Tensile test results showed that a twofold increase in tensile strength was obtained with an approximately 13 pct CNF reinforcement, despite there being no known bonding between CNFs and Cu. The transmission electron microscope (TEM) observations demonstrated that the C atoms in the CNF were forced into the Cu matrix, which caused the roughening of the CNF surface and the supersaturated solutionization of the Cu matrix in the vicinity of the CNF during liquid processing. A strong mechanical interlocking was believed to exist between the CNF and Cu due to the roughened surface of the CNF and the stress field developed around the CNF as a result of the supersaturated solutionization of the Cu matrix. This mechanical bonding mechanism appeared to be unique in the composite system reinforced with nano fibers produced by the liquid infiltration process.     

Characterization of diffusion induced grain boundary migration in the Ag/Cu system

The phenomenon of diffusion induced grain boundary migration (DIGM) when silver diffuses along copper's grain boundaries was confirmed through the characterization of the microstructure and the morphology of the migrated boundaries, the discontinuity and asymmetric character of the concentration profile, the dislocation configuration and the kinetics of migration by means of SEM, EPMA, TEM and AEM. The experimental results were discussed to prove the existence and the characteristics of DIGM in Ag/Cu system.     

雾化室内气压对Sn_(0.3)Ag_(0.7)Cu焊锡粉末雾化过程的影响

利用超音速气雾化装置制备了Sn0.3Ag0.7Cu无铅焊锡粉末,研究了雾化室内不同气压状态对粉末雾化过程的影响。结果表明:随着雾化室内部气压的逐渐增大,锥形雾化区由稳定逐渐趋于紊乱,锥形雾化区范围逐渐变大,气液流量比也随之增大,粉末球形度先变好后变差。当雾化室内部气压为0.05 MPa时,锥形雾化区稳定且雾化区范围大,粉末球形度最好。     

Modelling the influences of solid-state interdiffusion and dissolution on transient liquid phase sintering kinetics in a binary isomorphous system

A simple model was developed to predict the impact that solid-state interdiffusion and dissolution have on liquid formation and its duration during transient liquid phase sintering (TLPS). The model predicts that solid-state interdiffusion can dramatically reduce the amount of liquid initially formed during heating. This reduction is dependent on the heating rate and initial base metal particle size. In cases of sintering above the additive phase melting point, the model predicts that base metal dissolution increases liquid phase formation and that this additional melting reduces the base metal particle size. The model predicts that longer times are required to solidify isothermally the greater amounts of liquid formed at higher temperatures (because of dissolution). This agreed qualitatively with experimental results for a Ni-65 wt pct Cu TLPS mixture sintered at 1090 °C and 1140 °C. Quantitative comparisons between the model and experiment were good at 1140 °C; however, the rate of isothermal solidification was underestimated by the model for intermediate sintering times at 1085 °C.