The influence of additives on the reaction kinetics and for microstructure refinement in LiBH 4-MgH 2 composites is investigated in detail. Indications on the rate limiting processes during the reactions are obtained by comparison of the measured reaction kinetics to simulations with one specific rate limiting process. The kinetics of the sorption reactions are derived from volumetric measurements as well as from in-situ Xray diffraction (XRD) measurements. During desorption, the hydrogen is released at a constant rate, which possibly is correlated to the one-dimensional growth of MgB 2 platelets. In contrast, the kinetic curves of the absorption reactions exhibit the typical shape of contracting-volume controlled kinetics. The microscopical interpretation of kinetic measurements are supported by transmission electron microscopy (TEM) images confirming the formation of additive-nanostructures in the grain boundaries upon cycling. The present investigations underline the importance of the additives as nucleation substrates and the influence of the microstructure on the reaction kinetics.

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The barrier to heterogeneous nucleation of the β(Ti) phase on TiB(2) and other borides has been evaluated using the plane to plane matching model. The results are compared to the known nucleation of the α(Ti) phase on the β(Ti) phase. According to this comparison, the barrier to heterogeneous nucleation of the β(Ti) phase on TiB(2) can be judged to be small. This is in agreement with inoculation experiments. The addition of a Ti-Al-TiB(2) master composite to a β(Ti) solidifying TiAl based alloy leads to a significantly refined microstructure. Microsegregations enable us to attribute this refinement to refined equiaxed β(Ti) dendrites. However, model calculations based on the hemispherical cap model predict that the refinement via heterogeneous β(Ti) nucleation should be more potent. First calculations indicate that structural imperfections of TiB(2) particles limit the nucleation site diameter. Thereby, the nucleation barrier is increased and the refinement is less pronounced.

We investigate the impact of the surface roughness on the experimental value of the electrocapillary coupling coefficient, B. This quantity relates the response of electrode potential, E, to tangential elastic strain, e, and also measures the variation of the surface stress, f, with the superficial charge density, q. We combine experiments measuring the apparent coupling coefficient B eff for gold thin film electrodes in weakly adsorbing electrolyte with data for the surface roughness determined by atomic force microscopy and by the capacitance ratio method. We find that even moderate roughness has a strong impact on the value of B eff . Analyzing the mechanics of corrugated surfaces affords a correction scheme yielding values of B that are invariant with roughness and that agree with expectations for the true coupling coefficient on ideal, planar surfaces. The correction is simple and readily applied to experiments measuring B eff from surface stress changes in cantilever bending studies or from the potential variation in dynamic electrochemo-mechanical analysis.

Microstructure and texture formation were investigated in an intermetallic Ti-43.4Al-4.2Nb-1.1Mo-0.1B (in at.%) alloy after near conventional forging in the (a þ b) phase field region and subsequent isothermal annealing treatments at 1150°C for different holding times. During forging and the following cooling process a fine grained microstructure is formed consisting of lamellar a 2 /g colonies and elongated grains of the b o phase situated at the colony boundaries. The isothermal annealing treatment leads to a significant change of the forged microstructure. After hot-forging, all phases show typical fiber textures as it is expected for uniaxial deformation. In the as-forged state the a 2 (a) phase exhibits a h11-20i fiber, the b o (b) phase has a strong and sharp h001i fiber and the g phase shows a h110i and a weaker h101i fiber. After additional annealing at 1150°C for 8 h, the textures are almost unchanged in contrast to the microstructure. A. Gaitzenauer et al./Microstructure and Texture Evolution in an Intermetallic b-Stabilized g-TiAl Alloy ADVANCED ENGINEERING MATERIALS 2014, 16, No. 4