No abstract

The use of large beams in the Laser Powder Bed Fusion (L-PBF) process has been receiving increasing attention for the past few years and may widen the dissemination of this technology in the industry, as well as help increase the production volume. In this paper, a detailed comparison is presented between a usual 80 μm diameter Gaussian laser spot and a 500 μm diameter top-hat laser beam. The following benefits of a large and homogeneous beam could be demonstrated: (1) a moderate increase of productivity by reducing the number of scan lines, (2) a nearly total suppression of spatters and powder bed degradation (local loss of powder homogeneity caused by the redeposition of spatters) due to the low volume energy densities carried out and the limitation of deleterious vaporization effects, (3) the manufacturing of near fully dense Inconel 625 parts, especially in the hatching zones. Last, the occurrence of larger thermal effects induced by the large beam L-PBF was discussed by comparing two distinct definitions of the laser energy density: at a local (melt pool) scale, and at a global (the whole manufactured part) level.

No abstract

One-, two- or three-dimensional arrays of closely spaced silver nanoparticles may lead to new optical properties, due to short or long range coupling between their resonant surface plasmons, so that the spatially controlled growth of silver nanoparticles provides an efficient way to tune their optical properties. Towards this way, we present here the periodic pattern of a glass surface with silver nanoparticles by continuous ultraviolet laser exposure. The formation of the 160 nm period pattern is well described by an interference-based model which agrees with the experimental conclusions, mainly obtained by various forms of microscopy. Statistical approach based on the autocorrelation function gives quantitative description about the quality of the order in the periodic structure and about the nanoparticles averaged diameter (80 nm). We also present the optical extinction spectrum of the Laser Induced Periodic Surface Structure (LIPSS)-containing area of the glass, which unusually shows several bands in the visible range. The period of 160 nm of the periodic structure is short enough to allow coupling between nanoparticles, which makes it a possible candidate for plasmon-based optical applications.

No abstract

No abstract

International audienceRipples of period about 150 nm, formed at the surface of a silica-based glass, are reported. Our glass behaves like a metallic glass due to the formation of highly concentrated silver nanoparticles

[Publié en ligne le 09/03/2013]International audienceOnline UV/visible extinction measurement have been achieved during nanosecond Nd:YAG laser irradiation at 532 nm of a silver-exchanged silicate glass after each shot. We have explained the evolution of the integrated spectral evolution with the help of a few observed spots after the laser/glass interaction and completed them by optical and surface measurements. This optical method allows to in situ follow silver ions precipitation in nanoparticles (NPs) and the consequently surface plasmon resonance evolution (SPR). In this study, we focus on the interest of this method for one silver-exchanged soda-lime glass by direct observation of the sample surface. Scanning electron microscopy measurement and optical microscopy were used to identify the various ablation mechanisms. Profilometry was used to evaluate the material distribution and the surface roughness evolution (Rms parameter). Thus, we explain the silver NPs effect on glass matrix at various micrometric scales according to the deposited fluence and silver concentration