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Showing 6 results for Plasma Nitriding

H. Aghajani, M. Soltanieh, F. Mahboubi, S. Rastegari and Kh. A. Nekouee,
Volume 6, Issue 1 (3-2009)

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.
Arash Yazdani, Mansour Soltanieh, Hossein Aghajani,
Volume 6, Issue 4 (12-2009)

Abstract: In this research plasma nitriding of pure aluminium and effect of iron elemental alloy on the formation and growth of aluminium nitride was investigated. Also corrosion properties of formed AlN were investigated. After preparation, the samples were plasma nitrided at 550oC, for 6, 9 and 12 h and a gas mixture of 25%H2-75%N2. The microstructure and phases analysis were investigated using scanning electron microscopy and X-ray diffraction analysis. Moreover corrosion resistance of samples was investigated using polarization techniques. The results showed that only a compound layer was formed on the surface of samples and no diffusion zone was detected. Dominant phase in compound layer was AlN. Scanning electron microscopy results showed that nitride layer has particulate structure. These nitrided particles have grown columnar and perpendicular to the surface. It was also observed that the existence of iron in the samples increases the nitrogen diffusion, thus growth rate of iron containing nitrides are higher than the others. Corrosion tests results showed that formation of an aluminium nitride layer on the surface of aluminium decreases the corrosion resistance of aluminium significantly. This is due to elimination of surface oxide layer and propagation of cracks in the formed nitride layer
K. Taherkhani, F. Mahboubi,
Volume 10, Issue 2 (6-2013)

Nitriding is a surface treatment technique used to introduce nitrogen into metallic materials to improve their surface hardness, mechanical properties, wear resistance and corrosion resistance. In this research, the effects of plasma nitriding parameters including frequency and duty cycle were investigated on samples with different grooves dimensions. Steel blocks prepared from DIN1.2344 hot working steel were plasma nitride at 500 °C under the atmosphere contents of %75H2-%25N2, the duty cycles of 40%, 60%, 80%, and the frequencies of 8, 10 kHz for 5 hours. Then characteristics and micro hardness's of the nitrided samples were investigated using SEM, XRD, and Vickers Micro Hardness method. The results of the experiments indicated that with increasing frequency, the duty cycle, and the thickness of the grooves, the roughness of the surfaces increased. With an increase in duty cycle from 40% to 80%, the hardness of the surface rose and the thickness of the compound layer built up. Hollow cathode effect occurred in the samples with small grooves and high duty cycle in plasma nitriding. This will result in over heating of the sample which leads to a decrease in the slope of hardness values from the surface to the core of the sample and also a decrease in the diffused depth of nitrogen. The compound layer of the treated samples consisted of @ : Fe4N and : Fe2-3N phases and the proportion of the A to @ increased with the decrease in the duty cycle. Increasing the frequency did not affect the proportion of phases and micro hardness of the samples.
S. M. M. Shafiei, M. Divandari, S. M. A. Boutorabi, Naghizadeh,
Volume 12, Issue 2 (6-2015)

In this work, TiN/TiCN & PN/TiCN multilayer films were deposited by plasma- assisted chemical vapour deposition (PACVD). Plasma nitriding (PN) and TiN intermediate layer prior to coating leads to appropriate hardness gradient and it can greatly improve the mechanical properties of the coating. The composition, crystalline structure and phase of the films were investigated by X-ray diffraction. Atomic force microscopy and scanning electron microscopy were employed to observe the morphology and structure of the films. The TiCN layer exhibited a columnar structure. The adhesion force between the film and the tool steel substrate was 30.8 MPa for TiN/TiCN and 25.4 MPa for PN/TiCN film determined by pull off tests. The hardness of TiN/TiCN film was 12.75 GPa while it was 5.4 GPa for PN/TiCN film, respectively. The improvement of the adhesion in TiN/TiCN was attributed to a less gradient hardness configuration. In addition, the mean friction coefficients of the films were about 0.2 for TiN/TiCN and 0.3 for PN/TiCN film determined by nanoindentation tests.
M. Soltanieh, M. Kiani, M. Hasheminiasari,
Volume 14, Issue 2 (6-2017)

- The mechanism of diffusion layer growth in plasma nitrided coatings applied on a St52 steel using an active screen is investigated. The nitriding was performed at 450,500 and 550 ◦C temperature nitriding times of 5, 10 and 15 h, in a gas mixture containing 20 vol. % H2: 80 vol. % N2 and DC-pulsed plasma nitriding unit.

The surface, cross section and the thickness of diffusion of specimens was studied in terms of optical and scanning electron microscopy. According to the measurements of diffusion layer thickness, values of Q and D0 for nitrogen diffusion in substrate were calculated as 50585 (j/mol) and 4.11×10-10 (m2/s)respectively. The variations of depth of hardness during nitriding period was determined

A. Jafari Tadi, S.r. Hosseini, M. Naderi Semiromi,
Volume 14, Issue 3 (9-2017)

Influence of formation of surface nano/ultrafine structure using deep rolling on plasma nitriding and tribological properties of the AISI 316L stainless steel was investigated. Initially, the deep rolling process was carried out on the bar-shaped specimens at 15 cycles with 0.2 mm/s longitudinal rate and 22.4 rpm bar rotation. Then, plasma nitriding treatment was applied on the as-received and deep rolled kinds at 450 °C and H2-25% Vol. N2 gas mixture for 5­ h. Surface micro-hardness and un-lubricated pin-on-ring sliding wear tests were carried out on the as-received, deep rolled, plasma nitrided and deep rolled-plasma nitrided kinds. Results revealed that deep rolled-plasma nitrided kind is shown the highest wear resistance than the others, due to the further increased surface hardness achieved via the combined process.

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