Surface Conditions after LASER Shock Peening of Steel and Aluminum Alloys Using Ultrafast Laser Pulses.

Laser shock peening (LSP) is a mechanical surface treatment process to modify near-surface material properties. Compared to conventional shot peening (SP) the process parameters can be finely adjusted with greater precision and a higher penetration depth of compressive residual stresses could be reached. However, high process times of LSP leads to high production costs. In this study, ultrafast LSP (U-LSP) with an ultrafast laser source (pulse time in the picosecond range) was applied on specimens made of X5CrNiCu15-5 and AlZnMgCu1.5. The surface characteristics (surface roughness) and surface-near properties (microstructure, residual stresses, and phase composition) were compared to the as-delivered condition, to conventional laser shock peening (C-LSP), and to SP, whereas metallographic analyses and X-ray and synchrotron radiation techniques were used. The process time was significantly lower via U-LSP compared to C-LSP. For X5CrNiCu15-5, no significant compressive residual stresses were induced via U-LSP. However, for AlZnMgCu1.5, similar compressive residual stresses were reached via C-LSP and U-LSP; however, with a lower penetration depth. A change in the phase portions in the surface layer of X5CrNiCu15-5 after C-LSP compared to SP were determined.

In situ growth of catalytic active Au-Pt bimetallic nanorods in thermoresponsive core-shell microgels.

Here, we demonstrate that bimetallic Au-Pt nanorods (NRs) can be grown in situ into thermosensitive core-shell microgel particles by a novel two-step approach. In the first step, Au NRs with an average width of 6.6 ± 0.3 nm and length of 34.5 ± 5.2 nm (aspect ratio 5.2 ± 0.6) were homogeneously embedded into the shell of PNIPA networks. The volume transition of the microgel network leads to a strong red shift of the longitudinal plasmon band of the Au NRs. In the second step, platinum was preferentially deposited onto the tips of Au NRs to form dumbbell-shaped bimetallic nanoparticles. The novel synthesis forms bimetallic Au-Pt NRs immobilized in microgels without impeding their colloidal stability. Quantitative analysis of the catalytic activity for the reduction of 4-nitrophenol indicates that bimetallic Au-Pt NRs show highly enhanced catalytic activity, which is due to the synergistic effect of bimetallic nanoparticles. The catalytic activity of immobilized Au-Pt NRs can be modulated by the volume transition of thermosensitive microgels. This demonstrates that core-shell microgels are capable of serving as "smart nanoreactors" for the catalytic active bimetallic nanoparticles with controlled morphology and high colloidal stability.

Composites of metal nanoparticles and TiO2 immobilized in spherical polyelectrolyte brushes.

The synthesis and the catalytic activity of nanocomposites consisting of metal nanoparticles (Au, Pt, Pd) and nanoparticles of TiO(2) (anatase) is presented. These composite particles have been synthesized by reduction of the respective metal ions adsorbed on the surface of as-prepared TiO(2) nanoparticles that are immobilized on spherical polyelectrolyte brush particles (SPB) as carrier system. The SPB particles consist of a polystyrene core from which long chains of poly(styrene sodium sulfonate) are grafted. We demonstrate that the metal nanoparticles (such as Au, Pt, and Pd) are only generated on the surface of the anatase particles having a size of ca. 10 nm. These metal NP/TiO(2)@SPB composite particles exhibit a high colloidal stability. They are excellent heterogeneous photocatalysts for the degradation of the dye Rhodamine B under UV irradiation. The photocatalytic activity of the composite particles is 2-5 times higher than that of the pure TiO(2) particles. This finding is traced back to an enhanced adsorption of the dye on the metal@TiO(2) composites.