17 research outputs found
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Spectroscopic study of plasma nitrocarburizing processes with an industrial-scale carbon active screen
The active screen plasma nitrocarburizing technology is an improvement of conventional plasma nitrocarburizing by providing a homogeneous temperature distribution within the workload and reducing soot formation. In this study, an industrial-scale active screen (AS) made of carbon-fibre-reinforced carbon serves as the cathode as well as the carbon source for the plasma-chemical processes taking place. The pulsed dc discharge was maintained at a few mbar of pressure while simultaneously being fed with a mixed gas flow of hydrogen and nitrogen ranging from 10 to 100 slh. Using in situ infrared laser absorption spectroscopy with lead salt tuneable diode lasers and external-cavity quantum cascade lasers, the temperatures and concentrations of HCN, NH3, CH4, C2H2, and CO have been monitored as a function of pressure and total gas flow. To simulate industrial treatment conditions the temperature of the sample workload in the centre of the reactor volume was kept at 773 K by varying the plasma power at the AS between 6 and 8.5 kW. The resulting spectroscopically measured temperatures in the plasma agreed well with this value. Concentrations of the various species ranged from 6 Ă 1013 to 1 Ă 1016 cmâ3 with HCN being the most abundant species
Investigation on the laser ablation of SiC ceramics using microâRaman mapping technique
Group V Metal Oxides (V, Nb and Ta) doping od Titania Coatings by Means of Suspension Plasma Spraying
IFHTSE Global 21: heat treatment and surface engineering in the twenty-first century Active screen plasma nitriding and nitrocarburising of steels: an overview
Microstructure of Suspension Plasma Spray and Air Plasma Spray Al2O3-ZrO2 Composite Coatings
Titanium Dioxide Coatings Sprayed by a Water-Stabilized Plasma Gun (WSP) with Argon and Nitrogen as the Powder Feeding Gas: Differences in Structural, Mechanical and Photocatalytic Behavior
Cold spray coating of submicronic ceramic particles on poly(vinyl alcohol) in dry and hydrogel states
International audienceThis study demonstrates that cold spray technology offers a route to functionalize the surface of PVA pieces with ceramic (HA) coatings. Swollen PVA hydrogels could not sustain the heat and deformation produced by the spraying process. Dry PVA substrates, however, could be efficiently coated using a technologically relevant range of spraying energy parameters. By adjusting the fragmentation of the sprayed powder, one can produce fine HA coatings of submicron fragments embedded into the PVA substrate surface. The binding of these HA particles to the PVA substrate is strong enough to withstand swelling in water, enabling formation of HA-coated hydrogels by immersion in water after spraying. A microscopic picture of the coating formation is proposed, where the PVA substrate melts superficially within a microscopic layer and sprayed aggregates fragment upon impact with the substrate, therefore inducing surface roughening and strong binding of the HA fragments to the molten PVA layer. More generally, these results using one type of aggregated powder suggest that adjusting the nature of the sprayed powder (aggregate size, cohesiveness, porosity, composition, etc.) could be a promising strategy to tailor the morphology of such coatings produced by cold spray; For instance, thick layers could be deposited by cold spray on various substrates, including PVA and Ti-6Al-V, thanks to the binding action of residual byproducts of the chemical synthesis of HA particles (Ref 39). With the recent progress in the design of bioactive ceramics (Ref 40), such a cold-spray-based approach offers an interesting possibility to functionalize the surface of polymer implants with fine control of the ceramic composition and crystallinity