Papers by Keyword: Interdiffusion

Abstract: In this paper, the results of measurements of chemical diffusion of C in weldments of Fe- C-Mn alloys with content of 0-15 % Mn, are reported. Alloys were cast in induction furnace under protective Ar atmosphere. They were hot-forged to rods of diameter 15 mm, machined down to diameter 12 mm, and cut into pieces of 4 mm thickness. These cylindrical samples were metallographically polished. Diffusion couples, welded by electrical impulse, were sealed together with Ti-chips, into evacuated silica ampoules. After that, they were annealed at 1073-1373 K for 96-1.5 hours, respectively. Measurement of C redistribution was done in a normal direction to welding interface using electron-scanning microscope Philips SEM-505WDS equipped with Microspec WDX-2A. Diffusion coefficients of C were obtained and the relations between manganese and carbon were found.

Abstract: To prove the validity of Dayananda’s phenomenological model of interdiffusion in ternary systems the effective interdiffusion coefficients for a few diffusion couples in the system Cu-Ni-Fe, annealed at 1000 oC, are calculated on the basis of this model using available tracer diffusion and thermodynamic data. It is found that the calculated values of effective interdiffusion coefficients are in reasonable agreement with experimental values extracted independently from experimental concentration--penetration curves. Using the relationship between effective interdiffusion coefficients, tracer diffusion coefficients and thermodynamic factors, it is shown that thermodynamic properties of alloys play a significant role in interdiffusion processes in the system Cu-Fe-Ni.

Abstract: Ferromagnetic L10 ordered alloys are extensively studied nowadays as good candidates for high density magnetic storage media due to their high magnetic anisotropy, related to their chemical order anisotropy. Epitaxial thin bilayers NiPt/FePt/MgO(001) have been grown at 700 K and annealed at 800 K and 900 K. At 800 K, the L10 long-range order increases without measurable interdiffusion. At 900 K, the interdiffusion takes place without destroying the L10 long-range order. This surprising observation can be explained by different diffusion mechanisms that are energetically compared using molecular dynamics simulations in CoPt in the second moment tight binding approximation. In addition, the frequencies of the normal modes of vibration have been measured in FePd, CoPt and FePt single crystals using inelastic neutron scattering. The measurements were performed in the L10 ordered structure at 300 K. From a Born-von Karman fit, we have calculated the phonon densities of states. The migration energies in the 3 systems have been estimated using the model developed by Schober et al. (1981). The phonon densities of states have also been used to calculate several thermodynamic quantities as the vibration entropy and the Debye temperature.

Abstract: Tracer diffusion experiments have historically furnished much of the information about fundamental diffusion processes as embodied in such quantities as tracer correlation factors and vacancy-atom exchange frequencies. As tracer diffusion experiments using radiotracers are rather less often performed nowadays, it is important to be able to process other diffusion data to provide similar fundamental information. New procedures that are primarily based around the random alloy model have been established recently for analyzing chemical diffusion data in binary and ternary alloy systems. These procedures are reviewed here. First, we review the random alloy model, the Sum-rule relating the phenomenological coefficients and three diffusion kinetics formalisms making use of the random alloy. Next, we show how atom-vacancy exchange frequency ratios and then component tracer correlation factors can be extracted from chemical diffusion data in alloy systems. Examples are taken from intrinsic diffusion and interdiffusion data in a number of binary and ternary alloys.

Abstract: Solid-state diffusion is a subject of great interest for many intellectual merits and practical applications. It also provides excellent educational studies with cross-fertilization of science and technology. This paper examines the importance of multicomponent-multiphase interdiffusion with specific examples from materials and coatings for components in advanced energy production systems, including gas turbines and nuclear reactors. Results and analysis from laboratory experiments are presented in terms of interdiffusion fluxes, integrated interdiffusion coefficients, effective interdiffusion coefficients, and average multicomponent interdiffusion coefficients. Applications are highlighted for materials and coatings for components in advanced energy production technologies. Additional consideration is given to the refined approach to assess composition-dependent interdiffusion coefficients in multicomponent alloys.

Abstract: In this paper, we present and discuss some of the theoretical procedures that have been established recently for binary and ternary alloy systems for the purposes of analyzing chemical diffusion data (interdiffusion and intrinsic diffusion) alone and chemical diffusion data in combination with tracer diffusion data. Emphasis is put on extracting information about diffusion mechanisms by way of tracer correlation factors/vacancy-wind factors. Examples are taken from the intrinsic diffusion, interdiffusion and tracer diffusion data in the Ag-Cd and Ag-Cd-Zn, Fe-Ni-Cr and Cu-Fe-Ni alloy systems.

Abstract: The diffusivity of refractory elements in heat resistant steels is crucial for the basic understanding of the microstructural stability during creep. The purposes of this study are to estimate the diffusivity in Fe-Cr alloys as a base alloy for the bcc matrix phase in high Cr ferritic steels and also to investigate the alloying effect of Re on the W diffusivity in them. Fe-15Cr and Fe-20Cr binary alloys, Fe-15Cr-5Re, Fe-15Cr-5W, Fe-20Cr-5Re ternary alloys [mol%] were used in this study. On the basis of the modified ternary Boltzmann-Matano method, the interdiffusion coefficients were obtained in Fe-Cr-Re ternary system. The apparent interdiffusion coefficient for the Re-doped Fe-Cr-W alloy was about one fifth of that for the Re-free alloy. It is concluded that the existence of Re retarded significantly the W diffusion in Fe-15mol%Cr based alloy. This is probably the main reason why a small amount of Re addition suppress the microstructural evolution of W containing high Cr ferritic steels.

Abstract: Interdiffusion in Fe/Pt multilayer thin films has been studied. [Fe(1nm)/Pt(1.5nm)]20 multilayers were prepared by DC magnetron sputtering technique and subsequently annealed at temperatures of 543 - 633K in vacuum lower than 10-6 torr. X-ray diffraction (XRD) studies on these multilayer systems revealed the interdiffusion coefficients from slope of the best straight line fit of first peak intensity versus annealing time. The temperature dependence of interdiffusion in the range of 543 - 633K can be described by D=4.98×10-24 exp (0.88eV/kT) m2S-1. The coercivity, measured by Vibrating Sample Magnetometer, of the multilayer with annealing time at 603K increased, which is believed to the increase of surface roughness by interdiffusion at the interfaces of Fe and Pt multilayers, enhancement of composition gradient; and/or formation of Fe-Pt reaction phase at the interface of Fe and Pt.

Abstract: A diffusion-controlled growth of intermetallic phases and the role of the Kirkendall effect in morphological evolution of the product phase layers can be described in terms of an alternative theory considering chemical reactions at the interphase interfaces. Application of this “physicochemical” treatment to diffusional growth of intermediate phases with fairly wide homogeneity ranges is illustrated by the example of interaction in the Ag-Zn system. The model is purely phenomenological, and its use is convenient, since no explicit assumption of the underlying diffusion mechanism is required.

Abstract: Interdiffusion at the interface between a Co-36.5Ni-17.5Cr-8Al-0.5Y, MCrAlY coating and the underlying IN738 superalloy was studied in a large matrix of specimens isothermally heat treated for up to 12,000 hours at temperatures 875°C, 925°C or 950°C. Modelled results using the finite difference software DICTRA was compared with experimental average composition profiles measured across the interface using a new experimental approach.