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Content archived on 2024-04-15

Low temperature deposition or wear and corrosion resistant layers by vacuum assisted processed


Boron was selected for development as a wear and corrosion resistant layer, and titanium as a corrosion resistant layer. Boron shows very good adhesion to aluminium substrates, which simplifies the substrate pretreatment. Only degreasing of the substrate is necessary. The application of a thin aluminium layer onto steel substrates by sputtering works very well. Hence, the application of boron is not restricted to aluminium substrates. Titanium dioxide can be used for the protection of ceramic substrates against corrosion. The porosity of a deposited titanium dioxide layer is a function of the residual water vapour concentration in the reactor.

In plasma chemical vapour deposition emphasis was put on the deposition of titanium nitride films on M2 steel substrates. Gas mixtures of hydrogen, nitrogen and titanium tetrachloride were used at temperatures below 500 C. The influence of deposition parameters on layer properties was extensively investigated. Adhesion of the titanium nitride films on M2 steel can be improved by correct substrate cleaning and in situ discharge pretreatment or by application of a relatively high DC bias voltage on the substrates during the first 10 minutes of the titanium nitride deposition. Different plasma excitation sources such as radio frequency, DC and pulsed DC were studied. Very dense, pinhole free films could be deposited at a growth rate of 1 to 2 um/hr. The Knoop hardness (HK 0.025) was between 1500 and 2000 kg/mm{2}, and the critical load was above 40 N. The chlorine content of the films was below 2 wt%.

An alternative way to deposit titanium nitride films was by sputtering of titanium in a nitrogen gas atmosphere. Nitrogen isslowly introduced to facilitate the production of a graded interface layer. Coatings of 5 um were typically produced with zone 2 structure and dense morphology having a (22) preferred X-ray diffraction orientation. Critical loads of 60 N in scratch adhesion tests were usual. Film morphology was readily controlled by a combination of magnetron power, bias power and pressure settings such that open or closed structures could be achieved.

The carbides of refractory metals eg titanium and tungsten were deposited at 550 C by magnetron sputtering of the metal in an atmosphere of acetylene.

Work was done on the deposition of titanium nitride and tungsten carbon composites below 250 C on HSS. At even lower temperatures, 150 C, titanium nitride was deposited on aluminium substrates. The maximum thickness of the titanium-titanium nitride layers was 1 um. Titanium-titanium nitride on polycarbonate produced at 95 C had an open zone 1 structure and was l imited in thickness to 0.8 um. Aluminium has been coated onto nylon, cellulose lacquers and polycarbonate at 40 C to thicknesses of 0.31 um.

2 compounds were chosen for their potential possibilities as wear and corrosion resistant layers. Boron deposited from diborane at a deposition temperature of 400 C exhibits a high hardness (>2000 kg/mm{2}, HK at 50 gF). The adhesion of the boron layer of M2 steel substrate can be significantly enhanced by the application of a thin aluminium intermediate layer. The thickness of this layer has to exceed about 100 nm, related to the pinhole density of the thin film. Iron from the substrate which diffuses through the pinholes of the aluminium is thought to be responsible for the adhesion problem.

Titanium dioxide films deposited from titanium isopropoxide on M2 steel substrates at a temperature of 400 C show an extremely low adhesion to these substrates. Some improvement is obtained from special heat treatments such as RTA at 1000 C or in situ heat treatment at 750 C. Thin intermediate such as titanium or aluminium can give some improvement in adhesion. Corrosion tests indicate that the film structure, depending on the experimental conditions, is an important feature for the application of these films.
This project is aiming to develop processes which allow low temperature (below 500 Celsius degrees) deposition of wear and corrosion resistant coatings with various morphologies and stoichiometries, a uniform thickness distribution and a good adherence onto heat sensitive substrates (even plastics).
The following processes will be studied based on chemical vapour deposition (cvd) and physical vapour deposition (PVD).
- thermal low pressure CVD (LPCVD, MOCVD)
- plasma enhanced cvd (PCVD)
- hybrid PCVD-PVD for very low temperature processing.

Use will be made of the ability of CVD to coat complex shapes uniformly. This phenomenon will be an important factor in scaling up processes to an industrial proportion.


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Philips Gloeilampen Fabrieken NV
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5600 JM Eindhoven

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Participants (2)