Papers by Keyword: Growth Kinetic

Abstract: This study evaluates the boron diffusion in the Fe2B phase formed at the surface of AISI 1018 steels during the paste boriding process. The treatment was carried out at temperatures of 1123, 1173, 1223 and 1273 K with 2, 4, 5, 6 and 8 h exposure times for each temperature using a 4 mm layer thickness of boron carbide paste over the material surface. The boron diffusion coefficient Fe2B D was determined by the mass balance equation and the boride incubation time assuming that the boride layers obey the parabolic growth law, while the boron concentration profile along the interphase Fe2B/substrate was unknown. The boron diffusion coefficient was interpreted as a function of the treatment temperature, obtaining the activation energy value for diffusion controlled growth of Fe2B boride phase.

Abstract: Two boride layers were found to form at the interface of iiron-chromiium alllloys (10 and 25% Cr) or an industrial 13% Cr steel and boron at 850-950 oC and reaction times in the range 1-12 h. In the case of a Fe-10% Cr alloy and the steel, the layers are based on the FeB and Fe2B compounds. With a Fe-25% Cr alloy, the constituent phases are FeB and CrB for the outer layer and Fe2B and Cr2B for the inner layer. Both layers are characterized by a pronounced texture. Diffusional growth kinetics of boride layers are close to parabolic and can alternatively be described by a system of two non-linear differential equations, producing a good fit to the experimental data. The temperature dependence of the layer growth-rate constants obeys a relation of the Arrhenius type.

Abstract: The Ni3Sn4 intermetallic layer occurs at the interface of nickel and the saturated or undersaturated Sn-base solder melt at 250-450 °C and dipping times of 300 to 2400 s. Mathematical equations are proposed to evaluate the thickness of the Ni3Sn4 layer formed under conditions of simultaneous dissolution in the undersaturated solder melt.

Abstract: In the present work, a kinetic study based on a diffusion model was performed by use of both kinetics and thermodynamic data as input parameters, it was possible to evaluate the kinetic constant at each phase interface for a biphase configuration FeB and Fe2B grown over the surfaces of Armco Fe and Fe-Cr binary alloys at 0.5 and 4wt. %Cr by powder- pack boriding. The simulated values of the kinetics constants by the model were compared to those found in the literature and a good agreement was observed. For the Fe-4wt. %Cr alloy, it was found by simulation that the layer thickness ratio between the FeB and Fe2B phases is very sensitive to the increase of temperature and surface boron content.

Abstract: A modified cellular automaton model was proposed to simulate the dendrite growth of alloy. Different from previous models, this model used neither an analytical equation(such as KGT model) nor an interface solute gradient equation to solve the velocity of solid-liquid interface, but used the interface solute and energy conservation and thermodynamic equilibrium condition to describe the solid/liquid interface growth kinetics process. In present model, once the temperature field and solute field were solved by finite different method in the entire domain, the material thermodynamic properties can be substituted into four algebraic equations to easily determine the variation of solid fraction, interface temperature and solute concentration, instead of calculating interface moving velocity. As a result, the complexity of the calculation can be largely reduced. The simulated dendrite growth was in a good agreement with the Lipton–Glicksman–Kurz (LGK) model for free dendritic growth in undercooled melts.

Abstract: This study examined the growth kinetics of intermetallic phases that develop in solid-tosolid diffusion couples assembled with U-7, 10 and 12wt.%Mo vs. Al alloys (Al, Al-2wt.%Si, Al- 5wt.%Si, 4043 and 6061) after a diffusion anneal at 550°C for 24 hours. Based on interdiffusion microstructure and integrated interdiffusion coefficients, the addition of Si into the Al matrix alloy was observed to significantly reduce the growth rate of the intermetallic layer that primarily consisted of (U,Mo)Al4 phase. Growth rate of the (U,Mo)Al4 intermetallic layer also increases slightly with Mo content; however, it was not significant compared to the effect of alloying Si into Al alloys. Growth kinetics of (U,Mo)Al4 intermetallic layer appear highly sensitive to composition of U-Mo fuel alloy and Al cladding alloys, and must be an important criteria in alloy development/selection for optimum fuel performance with due consideration for compositiondependent multicomponent interdiffusion.

Abstract: Two borides FeB and Fe2B were found to form as separate layers at the interface between a 13% Cr steel and boron at 850-950 oC and reaction times up to 12 h. The chromium distribution within the boride layers is rather irregular. Its average content is 8 at. % in the FeB layer and 9 at. % in the Fe2B layer. Both layers are characterized by a pronounced texture. The strongest reflections are {002} and {020} for the orthorhombic FeB phase and {002} for the tetragonal Fe2B phase. Diffusional growth kinetics of boride layers are close to parabolic and can alternatively be described by a system of two non-linear differential equations, producing a good fit to the experimental data.

Abstract: A physico-chemical consideration of the interfacial interaction and diffusion resulting in the formation of chemical compound layers at the interface of initial substances A and B is presented. The layer-growth kinetics is shown to be much more complicated than it follows from conventional diffusional views neglecting interfacial reactions. In the majority of multiphase binary systems, layer occurrence appears to be sequential rather than simultaneous. Under conditions of diffusion control, the number of simultaneously growing compound layers at the A–B interface cannot exceed two. Multiple layers (three and more) can only form as a result of secondary processes connected with the rupture of a diffusion couple. In such cases, great care is necessary when calculating diffusion coefficients to avoid obtaining their physically meaningless values.

Abstract: Three-dimensional observations of proeutectoid ferrite formed at grain boundary in an Fe-0.09%C-1.48%Mn vanadium microalloyed alloy was revealed by techniques of serial sectioning along with computer-aided reconstruction. The ferrite allotriomorphs nucleated at grain boundary edges were approximately prolate ellipsoids. Not all the ferrite allotriomorphs formed at grain boundary faces were oblate ellipsoids. The growth kinetics of ferrite allotriomorphs nucleated at grain boundary edges was greater than that of ferrite allotriomorphs nucleated at grain boundary faces.

Abstract: In this work, an approach of reactive nitrogen diffusion is presented and applied to the iron gas nitriding process. A kinetic model based on Fick's laws is used to simulate the layer growth kinetics of a biphase configuration composed of ε and γ’ iron nitrides grown on the pure iron substrate. This diffusional approach, under certain assumptions, reveals the influence of the nitriding potential on the layer growth kinetics during the gas nitriding of pure iron. Some simulation results are presented and discussed.