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4728 |
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Wednesday, May 11, 2016, Room 3G 10:00 AM Wear Protection |
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Laser treatment of HVOF thermal sprayed nano-structured WC-12Co mixed with inconel-625 coatings for wear applications |
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Joseph Stokes / School of Mechanical & Manufacturing Engineering, National Centre for Plasma Science and Technology, Dublin City University, Ireland Naif Al Harbi* / School of Mechanical and Manufacturing Engineering, Dublin City University, Ireland Khaled Benyounis/ School of Mechanical and Manufacturing Engineering, Dublin City University, Ireland Lisa Looney/ School of Mechanical and Manufacturing Engineering, Dublin City University, Ireland |
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The HVOF thermal spray is gradually becoming one of the leading coating techniques used in place of the traditional electrolytic chrome plating (EHC), which has been used since the mid-19th century as coating or to reconstruct corroded components. Lately it has been realised that EHC emits mist and bath ions Cr+6 that have harmful effect on the human body. Despite the high quality coatings produced by the HVOF thermal spray system, its role has yet to be validated in the replacement of other traditional coating techniques where specific surface properties are required. One of the obstacles of the all thermal spray coating process is the porosity of the coated layer, which has major effect on its performance, especially in erosion/corrosion preventative applications. In this research, two coating materials have been prepared; Tungsten carbide cobalt (nano-structured) WC-12Co (InfralloyTM S7412) mixed with Nickle Chromium alloy (Diamalloy 1005- Inconel 625) to a weight percentage composition of 75% to 25% respectively, as previously optimised. These were used to produce very hard coatings deposited by HVOF thermally sprayed process onto carbon steel 4041 substrates. This work investigated the effect of laser post heat treatment on these coating, to enhance the wear/corrosion protective properties of the coating composition and to close the porosity. The substrates were laser treated with CO2 laser of 10.6 ¼m wavelength. Different outcomes of surface properties were achieved by varying the laser processing parameters. The parameters varied were the laser power, scanning speed and the pulse repetition frequency (PRF). The duty cycle was kept constant at 50% while the laser beam track was allowed to overlap by 40%, 50% and 60%. The morphological and metallurgical changes in the coating were examined by using sophisticated techniques such as SEM, EDS and XRD. The morphological and metallurgical changes examined include the microstructure, microhardness and the porosity before and after the laser treatment were observed. It was found that the porosity of the coated layer had significantly reduced after the laser treatment. Also, it was observed that the porosity and hardness were strongly affected by the laser parameters. Keywords: HVOF thermal spray coating, WC-12Co, Ni-Cr Inconel 625 alloy, laser post-heat treatment. N. Al Harbi , K. Y. Benyounis, L. Looney, J. Stokes School of Mechanical and Manufacturing Engineering, Dublin City University, Ireland. |