Defect and Diffusion Forum Vols. 237-240

Abstract: Iron self-diffusion measurements in amorphous and nanocrystalline chemically homogenous multilayers (CHM) of FeZr/57FeZr, (with nm range periodicity) have been studied with neutron reflectivity technique. It has been found that both the activation energy for diffusion and the pre-factor were significantly smaller as compared with bulk alloys. Effect of compressive stress on self-diffusion reveals a significant dependence on the activation energy as a function of applied stress. On the basis of the obtained results the diffusion mechanism in amorphous and nanocrystalline CHM of FeZr/57FeZr is reviewed in this paper.

Abstract: We will discuss the stress release phenomena, structural relaxation and interdiffusion processes during annealing. The [Co(4nm)/Ta(4nm)]38 multilayers were prepared by dc magnetron sputtering on Si substrate. The multilayers were annealed at various temperatures (523 - 673K) in vacuum (under 10-5 torr) furnace. The effective interdiffusion coefficients were determined from the slope of the best straight line fit of the first peak intensity versus annealing time [d ln(I(t)/I(0)) /dt] by X-ray diffraction (XRD) low angle measurements. The drastic decrease of the relative intensity in the initial stage shown due to the structural relaxation was excluded in the calculation of effective interdiffusion coefficients. The temperature dependence of interdiffusion in the range of 523 - 673K is described by D = 3.2×10-19 exp(-0.51±0.11 eV/kT) m2s-1.

Abstract: It was shown that external magnetic field of 5 kOe slows down the kinetics of grain boundary grooving in iron at 750 °C by about one order of magnitude. This observation is discussed in terms of magnetic effect in surface diffusion.

Abstract: The tracer diffusion of ion implanted deuterium is studied in amorphous and polycrystalline magnetron-sputtered Si3N4:H films with secondary ion mass spectrometry (SIMS). The experimentally obtained diffusion profiles are numerically simulated by computer calculations based on the concept of trap-limited diffusion where the tracer atoms form immobile complexes with: (a) intrinsic film defects like dangling bonds and (b) extrinsic defects caused by the implantation damage. For amorphous Si3N4:H films a moderately high dissociation rate of intrinsic complexes (dangling bonds) is present and time independent effective diffusivities are observed, which obey an Arrhenius law with an activation energy of DE = 3.4 eV and a pre-exponential factor of D0 = 4 x 10-4 m2/s. For polycrystalline Si3N4 films non-Gaussian depth profiles and strongly time dependent diffusivities are observed, which have their reason in the presence of intrinsic traps with negligible dissociation, presumably located at the grain boundaries.

Abstract: The experimental results on motion of single grain boundaries (GBs) of natural mechanical twin and single fabricated twin GBs as well as on fabricated twin GBs in system with triple junction (TJ) are obtained. The mobility of natural mechanical twin GBs, fabricated single GBs and fabricated GBs with TJ are compared. For the first time the effect of detachment of moving TJ and single natural twin GB from adsorbed atoms is reported. The results on single GB migration are considered in context of triple junction migration as the step to grain growth, i.e. “polycrystal” experiments.

Abstract: Diffusional growth of the grain boundary (GB) groove permits one to measure the ratio between GB energy sGB and surface energy ssur. The faceting of twin tilt grain boundaries in Cu has been studied using the GB thermal groove method. No rough facet edges were observed. It means that melting temperature is lower than the roughening temperature for the observed facets in Cu. The influence of orientation and misorientation deviation Dq = ½q – qS½ from coincidence misorientation qS has been studied. By increase of Dq the energy of (100)CSL facet increases. The convenient method for construction 3D three-dimensional Wulff diagrams was found. The 3- dimensional Wulff diagrams were constructed using this method and measured sGB / ssur values.

Abstract: During the last decade, the phase-field method has emerged across many fields in materials science as a powerful tool to simulate and predict complex microstructure evolutions. Since phase-field methodology has an ability to model complex microstructure changes quantitatively, it will be possible to search for the most desirable microstructure by using this method as a design simulation, i.e. through computer trial-and-error testing. In order to establish this methodology, the flexible quantitative modeling for various types of complex microstructure changes using the phase-field method must first be needed. In this study, as the typical examples for the modeling of the complex microstructure changes using phase-field method, recent simulation results for the diffusion controlled phase transformations and microstructure developments in magnetic materials are demonstrated.

Abstract: “Order-order” relaxations driven by atomic migration in superstructures proceed in nonsteady- state of a system, which relaxes to the equilibrium atomic configuration. Hence, the corresponding studies are complementary to standard steady-state diffusion investigations. Two time scales operating in “order-order” relaxations in L12-ordered (Ni3Al) and L10-ordered (FePd, FePt) binary intermetallics were experimentally observed. On the other hand, in B2-ordered NiAl – known of a giant vacancy concentration, “order-order” relaxations appeared surprisingly slow. Definite relationships between the activation energies for diffusion ( ) D A E and “order-order” relaxations ( ) O O A E − were revealed: ( ) D A E < ( ) O O A E − in L12-type superstructure; ( ) D A E ³ ( ) O O A E − in L10- and in B2-type superstructures. Corresponding simulation studies elucidated the specific atomistic mechanism of the processes. It has been shown that different time scales active in “order-order” relaxations in L12 and L10-ordered systems follow from specific atomic-jump correlations, which result from non-steady-state conditions and particular superlattice geometries: the availability of easy diffusion channels. A model of “order-order” kinetics in NiAl as controlled by a triple-defect mechanism is proposed.