Evaluation of the formation of compound coatings on aluminium by the new method of active screen plasma nitriding

In this paper, a composite coating of a mixture of AlN and Fe2-3N was created on Al1050 by plasma nitriding method using an active screen. The surface of aluminium samples was nitrided under the following conditions: gas atmosphere %20H(2)-%80N(2), at 550 degrees C, 80% duty cycle and the frequency of 10 kHz for 2, 5, 10 and 15 h. The coatings were characterized using grazing incidence x-ray diffraction, optical microscopy, field emission scanning electron microscopy, energy-dispersive spectroscopy, atomic force microscopy and nano-hardness. The dominate phase in the active screen plasma nitriding (ASPN) of compound layer was epsilon: Fe2-3N and AlN, additionally with increasing processing time, the thickness of compound layer was increased. According to FE-SEM results the sample surface was covered by nano sized iron nitride particle. The compound layer thickness ranges from 4.8 -/+ 0.4 mu m to 12.0 -/+ 1.4 for 2 h to 15 h of deposition process respectively. Moreover, the finest nitride particle size is about 124 -/+ 21.3 nm in diameter for the sample operated at 550 degrees C for 2 h and the size of the coarsest one is about 514.4 -/+ 72.2 nm in diameter belonging to the sample operated at 550 degrees C for 15 h. The results indicated that the samples were coated with a uniform distribution of polygonal nitride particles. This coating can improve surface properties.