van Fjj Frans Loo

Multiphase diffusion in binary and ternary solid-state systems

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Diffusion in the titanium-aluminium system—I. Interdiffusion between solid Al and Ti or Ti-Al alloys☆

Pure Ti as well as Ti—Al alloys have been coated in various ways with a pure solid Al layer and interdiffusion in the temperature range between 516 and 642°C has been investigated. In each case, a well adherent layer of TiAl3 is formed, growing according to a peculiar time-dependence. No other intermetallic compounds show up and no solid solution of Al in Ti arises. Two types of crystal structure of the TiAl3 layer have been found, depending on the temperature at which the layer was formed and on the composition of the starting alloy.

Diffusion in the titanium-aluminium system—II. Interdiffusion in the composition range between 25 and 100 at.% Ti

Abstract Interdiffusion phenomena have been investigated m the Ti-Al system in the region from 25 to 100 at.% Ti at temperatures between 700 and 1200°C. The phase diagram of the Ti-Al system has been constructed using data from concentration-penetration curves recorded for various types of diffusion couples. In the composition range ≲ 25 at.% Al, the phase diagram is found to agree with that proposed by Blackburn. In the Al-rich part of the diagram a phase Ti 2 Al 5 was found which is probably the same as the compound Ti 5 Al 11 reported by Schubert et al . The growth of the various diffusion layers is non-parabolic; the reason is supposed to be the influence of grain boundary diffusion. The latter decreases steadily with increasing annealing time as a result of grain growth in the layer. Ti is the most mobile element in the Ti 3 Al phase at temperatures between 768–865°C, whereas in the Al-richer compounds Al is the most mobile element at temperatures between 784–972°C.

The diffusion couple technique in phase diagram determination

The diffusion couple technique is a valuable experimental approach in studying phase relations in multicomponent systems. The use of different modifications of the method is illustrated by examples of phase diagram determination in various ternary systems. It is also shown that a number of error sources may appear when multiphase diffusion experiments are employed for constructing isothermal cross-sections. The difficulties connected with the concentration measurement at the interfaces and problems associated with the formation of a quasi-equilibrated diffusion zone are discussed. It is demonstrated that the efficiency of the diffusion couple technique is very high. However, in order to increase the reliability of the information obtained about a ternary diagram, a combination of the diffusion methods with an investigation of selected alloys is desirable.

Phase relations in the Ti-Si-C system

Abstract For the system TiSiC phase diagrams at 1373 K and at 1523 K were determined. For that purpose, several alloys and diffusion couples were equilibrated and analysed by EPMA (electron probe microanalysis) polarised light microscopy and X-ray diffraction. With EPMA the composition of the alloys could be determined accurately by measuring the titanium, silicon and carbon contents. Some differences were found with the known diagram from the literature.

Phase relations in the ternary TiNiz.sbnd;Cu system at 800 and 870 °C

Abstract We have investigated the isothermal cross sections through the ternary phase diagram Tiz.sbnd;Niz.sbnd;Cu at 800 and 870 °C by means of the diffusion couple technique. The results have been corroborated on essential points by the investigation of equilibrated alloys. Use has been made of optical, microprobe a nd X-ray analyses. The results differ from those mentioned in the literature. For two hitherto undescribed ternary intermetallic compounds X-ray diffraction data are given and crystallographic cell parameters are proposed.

Intrinsic diffusion and Kirkendall effect in Ni-Pd and Fe-Pd Solid solutions

Abstract Intrinsic diffusion and the Kirkendall effect in the Ni–Pd (at 900–1200°C) and Fe–Pd (at 1100°C) solid solution systems were investigated. The diffusion couple technique including incremental and “multi-foil” couples was employed. A theoretical analysis of the Kirkendall effect, which manifests itself by migration of inert markers inside the interdiffusion zone, was performed for a binary solid solution system. It was demonstrated that depending upon the relative mobilities of the components in different parts of the interaction zone of such binary diffusion couples, the appearance of two or more “Kirkendall” planes as marked by inert particles can be expected. This phenomenon, which indeed was predicted and found in the multiphase Ni/Ti diffusion couple, was not observed in the experiments on the single-phase Ni–Pd and Fe–Pd systems. The diffusion process in these binary systems exhibiting a minimum in the liquidus curve was found to show special features with respect to the concentration dependence of the diffusion coefficients.

Reactions and phase relations in the Ti-Al-O system

Abstract Reactions between titanium and alumina were studied experimentally for Al 2 O 3 substrates with a titanium-based coating and for planar Ti Al 2 O 3 diffusion couples in the temperature range between 800 and 1100°C. Isothermal sections through the phase diagram were determined by using these results as well as by investigating equilibrated alloys. These experimental sections agree with those calculated from thermodynamic data. The morphology and layer thickness of the observed reactions zones have been explained on the basis of these phase relations, making use of diffusion data from binary systems Ti O and Ti Al. The important role of the initial Ti thickness on the type of reaction products has been demonstrated.

Interface migration and the kirkendall effect in diffusion-driven phase transformations

Abstract An analysis is presented for the mass and vacancy fluxes within the reacting phases and at the interface for a diffusion-driven phase transformation between disordered binary solid solutions. As decided by the intrinsic diffusion coefficients and the initial and interface concentrations for each phase, vacancies must either be created or annihilated in the bulk phases but also at their interface. A general analysis is formulated for the growth or recession of a phase in terms of the Kirkendall reference frame and this result is compared to the analysis based on the reference frame centered on the number of moles. Specific example calculations demonstrate the various possibilities for vacancy creation/annihilation and for the growth/recession of phases. The growth rate expressed in the Kirkendall reference frame can be found by taking into account the associated vacancy exchanges for the interface reaction.

On the diffusion of carbon in titanium carbide

AbstractThe chemical diffusion coefficient of carbon in TiC1-y was determined as a function of stoichiometry and temperature in the range between 1000 and 1600°C using the diffusion couple technique. In marker experiments carbon was found to be virtually the only diffusing component. Accurate carbon analyses were performed using EPMA, both in diffusion couples and in the carbides present in equilibrated alloys. The homogeneity region of TiC1-y in this temperature range and the concentration profiles were accurately determined. From these profiles it is immediately clear that the diffusivity of carbon is a function of the carbon concentration. The interdifussion coefficient { % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfKttLearuatLrhDLjhih9gDOL2yG0evae% XatLxBI9gBamXvP5wqSXMqHnxAJn0BKvguHDwzZbqegm0B1jxALjhi% ov2DaeHbuLwBLnhiov2DGi1BTfMBaebbnrfifHhDYfgasaacH8srps% 0lbbf9q8WrFfeuY-Hhbbf9v8qqaqFr0xc9pk0xbba9q8WqFfea0-yr% 0RYxir-Jbba9q8aq0-yq-He9q8qqQ8frFve9Fve9Ff0dmeaabaqaci% GacaGaaeqabaWaaqaafaaakeaaiqGaceWFebGbaGaaaaa!3F06!