Laser Surface Nitriding of Ti–6Al–4V Alloy in Nitrogen–Argon Atmospheres

Surface-nitrided layers of Ti–6Al–4V alloy were fabricated using a diode laser in pure and mixed gas atmospheres of nitrogen and argon. The surface morphology, microstructure, hardness, and cracks of the nitrided layers were investigated. In all gas atmospheres, the layers showed smooth and humped regions, and consisted of planar nitrogen titanium (TiN), dendrites, and acicular martensite. The surface roughness was improved dramatically as the nitrogen concentration of the atmosphere was diluted with argon. Overall, the hardness of the nitrided layer was greatest for pure nitrogen and it tended to decrease as the concentration of argon in the atmosphere increased. However, the hardness of the layer for pure nitrogen also decreased rapidly, from the surface to matrix, in comparison to the diluted nitrogen atmospheres. It was shown that the number and size of dendrites, which determine hardness, are controlled by the nitrogen concentration. The dendrites of the nitrided layer were denser and smaller in a pure nitrogen atmosphere, than in diluted nitrogen atmospheres. Longitudinal and transverse cracks were observed in the nitrided layers. These two types of cracks were decreased or even eliminated as the argon concentration of the nitrogen–argon atmosphere was increased. Therefore, by diluting the nitrogen atmosphere with argon, the nitrided layer properties, in terms of surface roughness and cracks, can be improved, but this may also cause a reduction in the layer hardness.

The Influence of Ar on the Synthesis of Carbon-coated Copper Nanoparticles in Gaseous Detonation

Background: Carbon-coated metal nanoparticle is a kind of unique nuclear-shell material that is the carbon shell filled with metal particles. It has a great promising future in the application as excellent solid lubricants additives, conducting resin, antiradiation material and so on. As a mature technology, the gas detonation method has been widely used to synthesize various nanomaterials. Method: Using copper acetylacetonate as a precursor to provide carbon and different concentrations of argon as a protective medium for the first time, high quality carbon-coated copper nanoparticles (Cu@C) were synthesized in hydrogen and oxygen. X-ray Diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM) were employed to characterize the structure, phase and constituent of the Cu@C nanoparticles to investigate the influence of argon concentration on the synthesis. Results: The XRD pattern, Raman spectroscopy and TEM images confirm the effect of Ar on synthesizing Cu@C, especially on particle size. The minimum average size is around 13 nm, and most of the particle size distribution is in 5-10 nm range. When the argon concentration is high, the detonation process of H2 and O2 will be suppressed, which is not conducive to the graphitization. Conclusion: Argon gas has a catalytic effect on the synthesis of high-quality Cu@C, which could significantly reduce the particle size of detonation products; the grain size appears an obvious downtrend with the concentration of argon increasing, but the high concentration of Ar is disadvantageous for the graphitization of carbon shells.

A Statistical Study About Photocatalytic Properties of Titania Crystals Deposited by Sputtering

Crystallized titania layers were prepared by vacuum sputtering in a DC magnetron. Photocatalytic properties of the crystals were analyzed using degradation of formaldehyde in a self-conception reactor. All data were analyzed using classical curve dependence and statistical. This study used Anova to find correlations between photocatalytic properties of the crystals and deposition parameters. The considered parameters were pressure, temperature of substrate, argon concentration and time of sputtering, all of this measured during the active process.