Abdelouahed Chala

Corrosion and wear resistance of 32CrMoV13 steel nitrided by plasma

This paper presents corrosion and wear behavior of the plasma-nitrided 32CrMoV13 steel. Untreated and plasma nitrided samples were tested. The structure of layers was determined by X-ray diffraction, the morphology was observed by scanning electron microscopy (SEM). The corrosion behavior was evaluated by electrochemical techniques (potentiodynamic curves and electrochemical impedance spectroscopy). The corrosion tests were carried out in acid chloride solution (HCl 1 M). The plasma nitriding behaviors of 32CrMoV13 steel have been assessed by evaluating tribological properties and surface hardness by using a pin-on-disk wear machine and microhardness tester. Experimental results showed that the nitrides e-Fe2-3N and γ′-Fe4N present in the white layer are nobler than the substrate but may promote, by galvanic effect, a localized corrosion through open porosity. Better corrosion protection was observed for the nitrided sample. It is found that plasma nitriding improves the wear rate, and the presence of a hard and brittle compound layer on the surface causes an increase in wear of the specimen surface.

Effect of heat treatments on structural, microstructural and mechanical properties of Al 2017 alloy

The effect of ageing at 300°C before and after quenched at two temperatures of 180 and 280°C on the Al 2017 alloy was studied. The structural properties were investigated using X-ray diffraction; the microstructural evolution was investigated using scanning electron microscopy and microhardness measurement for the mechanical properties. After various states of ageing, the Al–Cu–Fe alloy shows significant changes in the microstructure and mechanical behavior. After ageing, the microstructure of the matrix consisted of a three solid solution of α-Al–Cu-Fe, β-AlFe and θ-A2Cu phases precipitations. After two-step heat treatment (quenching and ageing), the alloy reveals the formation of β and θ phases precipitates. After ageing at 300°C of original sample, the alloy reveals higher β precipitates, corresponding to the minimum value of microhardness, the volume fraction of this precipitates becomes higher. On the other hand, the TTT curves for the discontinuous and continuous precipitation reaction in this alloy have been suggested.

Effect of Doping of Nanoparticles on the Properties of Zn-Ni Composite Coatings

The purpose of this paper was to investigate the effect of Al2O3 and TiO2 nanoparticles contents on structural proporties, microhardness and corrosion resistance of Zn-Ni alloy coationg. Zn-Ni, Zn-Ni-Al2O3 and Zn-Ni-TiO2 composite coatings were electrodeposited on steel substrate by direct current in sulphate bath.The structure of the coatings was studied by X-ray diffration and by scaning electron miroscopy. The results showed the appearance of Ni5Zn21 phases and that the incrorporation of Al2O3 and TiO2 in the Zn-Ni coating refined the crystal grain size.The corrosion performance of coating in the 0.6M NaCl as a corrisive solution was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy EIS methods. It was found that the incorporation of nanoparticules in Zn-Ni alloy coating have better corrosion resistance and the values of Rct and Zw increase, while the values of Cdl decrease with increasing of nanoparticules.

Corrosion behavior of TiN-coated cutting carbide tools

Hard coatings produced by physical vapor deposition (PVD) have been widely used as a thin protective film. The coat- ings can provide wear resistance, corrosion resistance, can be decorative and act as a diffusion barrier. Among the commercially available coatings, TiN (titanium nitride) is probably the most commonly used industrially for machining tools. The aim of our work is to study corrosion resistance of TiN coated carbide tools such as WC-Co (tungsten carbide with cobalt). The corrosion behavior of TiN coating was examined in naturally aerated aqueous 0.5 M NaCl solution. The study was performed by using potentiodynamic polarization (PP) and electrochemical impedance spectroscopy measurements (EIS), complemented with scan- ning electron (SEM) microscopy. The experimental impedance data are in good agreement with the polarization experiments. The TiN coating improves the corrosion resistance of carbide tools in NaCl solution.