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Low temperature deposition of wear and corrosion resistant layers by vacuum assisted processes

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.

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