Smooth, well adhering CVD diamond coatings on steel and non-carbide forming substrates (NNS.4041)
Project nummer:
nns4041
Omschrijving van het onderzoek
By application of thin diamond films as a coating on machine parts or devices to be used under severe chemical and mechanical conditions, the wear and the corrosion resistance of the surfaces is highly improved. Diamond coated products are presently based on hard metals or cemented carbides (Co<7%/(W)Carbides<10%; or by brazing sintered diamond powder; Diamond Like Carbon). The aim of the project is to obtain smooth, well adhering CVD grown diamond layers on steel and non-carbide forming substrate materials (Mo and Si carbide forming) by the application of interlayers.
- The surface finish of the diamond layers will be optimized by active control of the texture, size and morphology of the grains during growth or by in-situ post-growing etching.
- A better fundamental understanding of substrate/interlayer/coating systems in general and that of the steel/interlayer/CVD diamond system in particular, will be pursued within the project in order to optimize the adhesion of the (polycrystalline) diamond coatings.
Flame deposition is a technique capable of diamond growth at a rate > 100 µm/hr. The TA will develop an upscaled combustion torch and a device related cooling system. The hot-filament equipment (HFCVD) is capable of deposition over several cm2 at several µm/hr. In parallel the marketing department of the Nijmegen Business School will perform a market analysis to obtain an optimal match between the technical research performed and production or performance limiting problems encountered by industrial companies. In the final stage several utilities will be coated and tested at TNO Industrie in Apeldoorn.
Resultaten van het onderzoek
It has been recognised that the main aim of this project, for the first couple of years, is to find an interlayer which
- forms a diffusion barrier for Fe at substrate deposition temperature to avoid graphitisation
- can bear and minimise the thermal stresses which occur upon cooling down from substrate deposition temperature
- can be deposited on steel, and
- forms a substrate on which diamond can be deposited.
Although not of immediate importance, with a view on the utilisation, a fifth requirement may be
- the restriction of the costs for producing such a layer on steel.
Finally, from a practical point of view
- it should be possible to remove the layer during deposition in case something goes wrong.
With the aim to establish which layer would match the above mentioned requirements, it appeared that a chromium nitride layer would be most suitable. It is, at least in principle, possible to produce a layer with a gradient in composition and properties varying from chromium on the steel side to chromium nitride on the diamond side.
Chromium can be deposited on steel by means of electroplating and subsequently this layer can de nitrided at high temperature by means of an ammonia flow. Also Physical Vapour Deposition techniques can be employed to deposit chromium on steel and by adding nitrogen the composition and properties can be modified.
So far, we have been exploring the possibility of diamond deposition on nitrided chromium using the oxyacetylene flame deposition technique and on PVD CrN and CrCN coated steel using the hot filament reactor.
Rounded steel (toolbit) samples (2.5 cm2) have been coated with PVD CrN by means of ion plating and magnetron sputtering. First results on the ion plated CrN samples show that diamond deposition is indeed possible. Deposition runs were performed for 3.5 hours at 700-800 °C with 0.5% CH4 in 99.5% H2. The SEM micrographs and Raman measurements show good quality diamond films with well-faceted crystallites varying in size from about 0.5 µm to 2.0 µm. The adhesion of these films is sufficiently high to withstand the scotch tape test. The obtained diamond layers were not fully covering the surface, but this can be solved by applying longer deposition times. From these results we can conclude that the ion plated CrN on top of the steel acts as a good diffusion barrier for Fe, as no abundant graphite formation is observed. Next to that, good bonding between the ion plated CrN and the deposited diamond is obtained and no delamination of the diamond films is observed. So, the interlayer system based on ion plating of CrN seems to fulfil requirements 1 to 4, as stated in the first paragraph.
SEM micrograph of diamond coating on PVD CrN coated steel (diamond deposition at 700 °C for 3.5 h)
Gebruikers
Bij dit onderzoek zijn acht bedrijven betrokken.
Projectleider
Dr. J.J. ter Meulen
Katholieke Universiteit Nijmegen
Vakgroep Molekuul- en Laserfysica
Toernooiveld 1
6525 ED NIJMEGEN.
Status van het project
| Gestart | : 15-08-1997
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| Einddatum | : 01-12-2002
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Trefwoorden
coating, corrosie, diamant, hechting, P Materiaalonderzoek, materiaalwetenschappen, molecuulfysica, laserfysica, tribologie, depositietechnologie, oppervlaktebehandeling, chroom nitride, tussenlaag, thermische spanningen.
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