Highly Regular Hexagonally-Arranged Nanostructures on Ni-W Alloy Tapes upon Irradiation with Ultrashort UV Laser Pulses.

Nickel tungsten alloy tapes (Ni-5 at% W, 10 mm wide, 80 µm thick, biaxially textured) used in second-generation high temperature superconductor (2G-HTS) technology were laser-processed in air with ultraviolet ps-laser pulses (355 nm wavelength, 300 ps pulse duration, 250-800 kHz pulse repetition frequency). By employing optimized surface scan-processing strategies, various laser-generated periodic surface structures were generated on the tapes. Particularly, distinct surface microstructures and nanostructures were formed. These included sub-wavelength-sized highly-regular hexagonally-arranged nano-protrusions, wavelength-sized line-grating-like laser-induced periodic surface structures (LIPSS, ripples), and larger irregular pyramidal microstructures. The induced surface morphology was characterized in depth by electron-based techniques, including scanning electron microscopy (SEM), electron back scatter diffraction (EBSD), cross-sectional transmission electron microscopy (STEM/TEM) and energy dispersive X-ray spectrometry (EDS). The in-depth EBSD crystallographic analyses indicated a significant impact of the material initial grain orientation on the type of surface nanostructure and microstructure formed upon laser irradiation. Special emphasis was laid on high-resolution material analysis of the hexagonally-arranged nano-protrusions. Their formation mechanism is discussed on the basis of the interplay between electromagnetic scattering effects followed by hydrodynamic matter re-organization after the laser exposure. The temperature stability of the hexagonally-arranged nano-protrusion was explored in post-irradiation thermal annealing experiments, in order to qualify their suitability in 2G-HTS fabrication technology with initial steps deposition temperatures in the range of 773-873 K.

Effect of self and dual-curing on degree of conversion and crosslink density of dual-cure core build-up materials.

PURPOSE: Dual-cure core build-up resins have been developed to take advantages of both self and light-cured resin. The aim of present study was to determine the polymerization characteristics of self and dual-cured modes of dual-cure core build-up composites evaluating degree of conversion (DC) and crosslink density by measurement of glass-transition temperature (Tg) and hardness decrease in ethanol. METHODS: Clearfil Dc Core Automix (CLF) and Grandio Core Dc (GR) core build-up resins were selected. Twelve specimens for both composites were polymerized using quartz-halogen-tungsten light curing unit (QTH) and 12 specimens polymerized chemically. DC was determined by ATR-FTIR spectroscopy. TG/DTA analysis was performed to determine Tg. Microhardness value of specimens was determined by Vickers-tester before and after specimens stored in absolute ethanol for 24h. RESULTS: One-way ANOVA showed no different DC values between dual and self-cured mode of GR and dual-cured CLF composites had higher DC than self-cured mode. Tg and percentage of softening in ethanol values of GR and CLF revealed significant difference between self and dual-cured mode. CONCLUSIONS: In comparison of GR and CLF, DC showed no statistical difference in both curing modes. However, dual and self-cured GR has statistically higher Tg values and lower percentage of softening in ethanol than CLF. Polymerization characteristics of dual-cure core build-up composites have superiority in dual-cured mode than self-cured.