Iranian Journal of Materials Science and Engineering

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Abstract: Formation of a hybrid coating by the use of plasma nitriding and hard chromium electroplating on the surface of H11 hot work tool steel was investigated. Firstly, specimens were plasma nitrided at a temperature of 550 °C for 5 hours in an atmosphere of 25 vol. % H2: 75 vol. % N2. Secondly, electroplating was carried out in a solution containing 250 g/L chromic acid and 2.5 g/L sulphuric acid for 1 hour at 60 °C temperature and 60 A/dm2 current density. Thirdly, specimens were plasma nitrided at a temperature of 550 °C for 5 and 10 hours in an atmosphere of 25 vol. % H2: 75 vol. % N2. The obtained coatings have been compared in terms of composition and hardness. The compositions of the coatings have been studied by X-ray diffraction analysis. The surface morphology and elemental analysis was examined by using scanning electron microscopy. The improvement in hardness distribution after third step is discussed in considering the forward and backward diffusion of nitrogen in the chromium interlayer. Also, the formed phases in the hybrid coating were determined to be CrN+Cr2N+Cr+Fe2-3N+Fe4N.

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Abstract:

activity gas diffusion process has been investigated in this research. Effects of coating temperature and aluminum

concentration in powder mixture on formation mechanism were studied using optical and scanning electron

microscopes, EDS and X-ray diffraction (XRD) techniques. For this purpose two different packs containing 1 and 2

wt% aluminum powder, were used for coating the samples at two temperatures, 850ºC and 1050ºC. The ratio of Al to

activator was kept constant in both packs. By increasing the Al content in high activity powder mixture, the

concentration of diffused Al increased in the coating layers, and the thickness of coating increased. At 1050ºC as the

rate of diffused Al to the interdiffusion zone increased, this zone gradually transformed to outer coating phases. At

850ºC coating formed by inward diffusion of Al, but at 1050ºC it was initially formed by inward diffusion of Al followed

by outward diffusion of Ni.

Formation mechanism of an aluminide coating on a nickel base superalloy IN738LC via a single step high

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The objectives of this research were to find an economical way of reducing porosities in the microstructure of coatings deposited by flame spraying technique on CK45 steel and also trying to increase their cohesive strength to the substrate, so that the overall wear properties of this type of coating can be improved. So several specimens from this steel coated with NiCrBSi powder under specific conditions were subjected to various furnace heat treatment at 1000, 1025, 1050, 1075 and 1100 °C, each for periods of 5, 10 and 15 minute before cooling them in air. Tribological properties of treated coatings were evaluated by pin on disc method. The results show the highest wear resistance and microhardness values observed in one of the sample was due to lower amount of porosity and higher amount of very fine Cr2Ni3B6 particles precipitated homogeneously throughout its microstructure during specific heat treatment.