2015-Sustainable Industrial Processing Summit
SIPS 2015 Volume 6: Coatings, Cement, Rare Earth & Ferro-alloys
| Editors: | Kongoli F, Yildirim H, Hainer S, Hofmann K, Proske T, Graubner C.A., Albert B |
| Publisher: | Flogen Star OUTREACH |
| Publication Year: | 2015 |
| Pages: | 200 pages |
| ISBN: | 978-1-987820-29-4 |
| ISSN: | 2291-1227 (Metals and Materials Processing in a Clean Environment Series) |
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Reactive Very Low Pressure Plasma Spraying for Manufacturing Nitrides Containing Composite Materials: Case of Ti Tixny Nitrides Coatings
Ghislain Montavon1; Marie-Pierre Planche1; Aurelie Quet2; Luc Bianchi2;1BELFORT-MONTBELIARD UNIVERSITY OF TECHNOLOGY (UTBM), 90010 Belfort cedex, France; 2CEA/DAM, 37260 Monts, France;
Type of Paper: Regular
Id Paper: 37
Topic: 19
Abstract:
Titanium-based nitride coatings exhibit peculiar properties at elevated temperatures which make them relevant candidates for various high-temperature applications, in thermal solar energy converters as a highly stable plasmonic absorder, in biomass energy converters as catalyst to fasten the hydrocarbons pyrolysis process in view of reducing the formation of polyaromatic hydrocarbons and soot, in generic applications for which thermal conductive coatings with high resistances to oxidation and high hardnesses are mandatory.
Vapor deposition processes are the common processes to manufacture coatings made of Titanium-based nitrides. Nevertheless, those processes exhibit two main drawbacks, maximum coating thicknesses limited to a few micrometers on the one hand and a rather low deposition rate (i.e., a few grams per hour) on the other one.
On the contrary, plasma spray processes allows manufacturing thick coating (i.e., a few hundreds of micrometers) at a relatively elevated deposition rate (i.e., a few kilograms per hours). Nevertheless, those deposition processes are unsuitable for processing incongruent materials, such as nitrides.
A solution relies in the formation in situ of those materials, in other words in alloying the metallic feedstock with Nitrogen during deposition. This corresponds to a so-called reactive deposition process. Several attempts were made during the 90's, and since then, to manufacture such coatings by implementing an atmospheric plasma torch equipped with a shroud into which the nitriding reaction can take place. Such an approach, up to now, has never been fully successful: the complex fluid dynamics within the shroud together with the necessity to cool it down made those systems difficult to operate (i.e., clogging, etc.) and never allowed to alloying the in-flight particles in a large extend since the chemical interaction occurs at the periphery of large molten particles, a process known for being inefficient from the thermodynamic point of view. The very low pressure (i.e., in the range of 50 to 150 Pa) plasma spray process allows manufacturing metallic coatings by condensation of vapors resulting from the full or partial vaporization of feedstock particles in the core of the plasma flow. The strong expansion of the plasma, under such a low pressure, allows carrying the vapors over long distances (i.e., > 1 m). This physical state (rather high enthalpy, gaseous species, etc.) together with a long interaction time due to the plasma plume length can promote the chemical reactivity. Several research institutes consider nowadays this second approach as a more relevant one.
This paper aims at presenting recent results with the primary goal of better understanding physical mechanisms occurring during the reactive deposition process of Titanium with Nitrogen. Optical emission spectroscopy was implemented to better identify the reactive mechanisms. Coatings, with up to 25% at. of Nitrogen, were manufactured and their structure was evaluated in terms of phases content (XRD), Nitrogen content (GD-OES), as well as hardness values. TiN and TiN0.3 nitrides were identified in the coatings and are formed in- flight by gas-gas reactions. Ti2N nitrides were also identified in the coatings and are formed by solid-gas reactions.