Search

Heterogeneous structure is practical to improve the strain hardening abilities of materials due to the effect of hetero-deformation induced hardening, especially of composites. In this study, a series of TiB/TC4 composites with a pseudo core–shell structure of bimodal grain distribution were fabricated via a two-step ball-milling and spark plasma sintering. The synthesized TiB/TC4 composites have a structure of coarse lamella α-Ti grains of average 23.6 μm in diameter surrounded by fine α-Ti lamella grains of average 4.2 μm, with TiB distributed on the primary TC4 surface areas. TiB/TC4 composites with 0.4 wt% TiB2 exhibited the best comprehensive mechanical properties with an ultimate tensile strength of 1161.95 MPa (a 35.1% increase compared with that of pure TC4) and an elongation of 7.57%. In conclusion, the pseudo core–shell structure improved the strength by improving the strain-hardening abilities, achieved by the coordinated deformation between coarse grains and fine grains.

Highly porous Cu foams comprised of interconnected branched dendrites were used as sacrificial templates for the fabrication of pseudo core-shell Cu@Pt and Cu@Pt-Ru unsupported electrodes by galvanic replacement. The as-prepared materials presented a three-dimensional structure with pores between 17 and 45 μm made of superimposed layers of ramified dendrites. TEM analysis showed that the dendrites were composed of agglomerates of grains of about 4 nm in size and mesopores of ca. 30 nm in diameter. The as-prepared 3D electrodes were tested for methanol oxidation in acid media at different temperatures. The results showed that the catalytic activities of Cu@Pt and Cu@Pt-Ru foams normalized to the electrochemical surface area are almost 50 % higher than that of a commercial Pt−Ru/C material, with poisoning rates that are reduced by half in the same potential range. The enhanced behavior of the as-prepared foams is believed to be the result of the influence of copper atoms on the reactivity of platinum sites, the highly defective structure of the electrodes, as well as the facilitated diffusion of methanol molecules and the products formed during the reaction throughout the highly porous three-dimensional structure of the electrode. The apparent activation energies ( Ea,app) for the methanol oxidation reaction (MOR) were determined by potentiostatic experiments. Ea,app values of 29.07 and 24.20 kJ mol−1 were calculated for Cu@Pt and Cu@Pt-Ru foams at 0.3 V, respectively. The results suggested that the MOR is governed by the dissociative adsorption of methanol as a result of the multifunctional nature of the catalyst and the facilitated diffusion of the products formed during the reaction. [ABSTRACT FROM AUTHOR]