[en] Enhancing tensile strength is crucial to increasing the applicability of nanoporous materials including nanoporous gold (np-Au) that show mechanical weakness because of their nanoporous structure despite other superior characteristics. We fabricated twinned and textured np-Au foils with an average twin spacing of 7.9 nm. The foils exhibit an ultimate tensile strength (UTS) of 87.5 MPa when the loading axis is normal to the twin boundaries. This UTS value is approximately three times greater than that for np-Au with rare twins of 27.4 MPa. The high UTS can be ascribed to the twin boundaries acting as effective barriers to dislocation slip, resulting in the strain-hardening of the load-bearing ligaments.

[en] Stretch-flangeability as a parameter of formability is measured on dual-phase (DP) and complex-phase (CP) steels by the hole-expansion ratio (HER), and nanoindentation is introduced to assess the hardness of constituent phases before and after HER testing. Hole-expansion ratios of two dual-phase (DP1, DP2) and one complex-phase (CP1) steels are measured as 51%, 126% and 136%, respectively. The primary site of void formation is found to be the interfacial boundary for DP1, the ferrite phase close to the martensite phase where numerous geometrically necessary dislocations (GNDs) are formed for DP2, and the martensite phase for CP1. The hardness ratio of the hard to soft phase is a key indicator of formability, and this introduces the stress concentration from strain disparity at the interfacial boundaries between the hard and soft phases. Here, it is founded that strain-hardenability of constituent phases depends on the hardness of the GND layer, and the strain disparity under deformation is determined by the GND layer hardness as well as the hardness ratio of the hard to soft phase. This study suggests the GND layer as a stress-dispersion layer and the hardness of GND layers in soft phases as a critical role in formability.

[en] Barium titanate (BaTiO₃) has attracted considerable attention as a perovskite ferroelectric ceramic material for electronic multilayer ceramic capacitors (MLCCs). Fine BaTiO₃ nanopowders with a considerably high tetragonality directly influence the typical properties of nanopowders; however, their synthesis has remained challenging. In this study, we analyzed the effect of two different TiO₂ powders with anatase and rutile phases in a solid-state reaction with barium carbonate (BaCO₃). The effect of the particle size ratio (TiO₂/BaCO₃) of the raw materials on the tetragonality and particle size of the as-synthesized BaTiO₃ powders was also determined through extensive characterization of the powders by X-ray diffraction, field-emission scanning electron microscopy, and Raman spectroscopy. The present investigation reveals that the design BaTiO₃ structure is expected to advance the development of efficient catalytic and sensor materials for sustainable environmental applications.