Oxidation behaviour of PACVD TiBN coating at elevated temperatures |
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Authors: | Y. He J. Zhou T. Walstock J. Duszczyk |
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Affiliation: | aDepartment of Materials Science and Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft, The Netherlands;bAdex B.V., Tjalkkade 2, 5928 PZ Venlo, The Netherlands |
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Abstract: | The elevated-temperature oxidation behaviour of a TiBN coating on a plasma-nitrided hot-work tool steel (DIN 1.2367) by means of plasma-assisted chemical vapour deposition (PACVD) was investigated under the condition where a coated die would be preheated prior to being mounted on the press for aluminium extrusion. The TiBN coating was found to possess good resistance to oxidation up to 400 °C. Rapid oxidation started to occur at 450 °C. Radio frequency glow discharge optical emission spectroscopy (rf-GDOES) indicated that the oxidised layer was thickened from 100 nm to 1.0 μm, as the soaking time at 500 °C was prolonged from 2 to 16 h, which was attributed to the high temperature that promoted the penetration of oxygen into the coating. rf-GDOES also showed that boron initially in the coating vanished from the oxidised layer when the temperature was 450 °C or higher. X-ray diffractometry confirmed that the oxidised layer was composed mainly of TiO2. SEM revealed that the TiO2 layer was pulverised, leaving many microcracks and cavities, as a result of the losses of boron oxide and nitrogen. The rapid oxidation at above 450 °C was attributed to the pulverised TiO2 layer that was unable to hinder the diffusion of oxygen into the coating. It is therefore recommended to apply a protective gas during the preheating of the TiBN-coated die for aluminium extrusion. Alternatively, an advanced TiBN coating with enhanced resistance to oxidation must be developed, which will be conducive to its application for aluminium extrusion dies. |
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Keywords: | PACVD TiBN Oxidation Thermal treatment |
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