Résumé: Carbon films were deposited on Si (111) wafers by microwave electron cyclotron resonance/plasma assisted chemical vapour deposition using a benzene–argon gas mixture with different argon flowrates (5, 15 and 30 sccm). The structure, surface morphology and hardness were studied. The film surface has been characterised by Raman spectroscopy to study the hybridisation of carbon in the film, and Fourier transform infrared spectroscopy was conducted to obtain bonding characteristics. The morphology of the films has been inspected by atomic force microscopy.

Résumé: Combustion in thermal explosion mode of the mixtures (Ti–Cr–Mo–W-graphite) under low uniaxial pressure of 19 MPa was used to produce cemented carbides (complex carbides/iron–nickel alloy). The results of the investigations showed that ignition (Tign) and combustion (Tmax) temperatures, as well as material density, structure and properties, were sensitive to the iron–nickel additions. When the iron–nickel content increases, combustion is characterized by a lowering from Tign and a reduction in reactions heating effect. The carbide formation was carried out by selective mechanism. Carbides of titanium (TiC) and chromium (Cr23C6) were formed instantaneously during the exothermic peak. However, the molybdenum carbide (Mo2C) and mainly the tungsten carbide (W2C) resulted from incomplete carbon diffusion in solid state. An isothermal maintenance under pressure at 1373 K, has allowed to accelerate the material densification mechanisms by viscous flow. At the same time, it completed the carbides formation thanks to the carbon diffusion mechanism as shown by the presence of new phases such as WC and Cr7C3. The maximum effect of densification was observed for a binder content of 50 wt.%, where the relative density of product attained 95%. The Vickers hardness (HV0.15) depends also on the binder content and varies from 6300 MPa to 19,000 MPa. The best tribological behaviour was achieved on cermets with 30% (Fe–Ni).

Résumé: The microstructure and wear behavior of a manganese and niobium alloyed high chromium cast iron were examined and compared to an as-cast chromium cast iron. Three heat treatments were applied: quenching at 930, 980 and 1030 °C followed by tempering at 250 °C. The microstructures were characterized by optical and scanning electron microscopy equipped with an energy dispersive spectrometer. The Vickers microhardness (HV) were measured. X-ray diffraction tests were carried out in order to identify the nature of the existing crystallographic phases in each studied sample. The tribological behavior was studied in the dry state under a load of 10 N at room temperature. The friction coefficient was recorded. The wear mechanism of the investigated is observed by optical microscopy. The obtained results show that the as-cast microstructure of the studied chromium cast iron samples consists of an austenitic matrix and a complex eutectic carbide network of M7C3 type. The applied heat treatments have affected the microstructure and have promoted the formation of martensite, retained austenite and secondary precipitations. The addition of niobium and manganese also shows a refinement on the microstructure, this effect is observed on the dimensions of the dendrites which appear finer in the chromium cast iron alloyed with Mn and Nb.

Résumé: The effects of boriding and boronitrocarburising surface treatments on the microstructure and mechanical properties of AISI 4130 steel have been investigated. Pack boriding was carried out at 1223 K for 5 h and 8 h, while the double treatment of boronitrocarburising consisted of salt bath nitrocarburising at 853 K for 6 h followed by pack boriding at the same temperature and times as the boriding treatment. Microstructure examination of the borided and boronitrocarburised layers was carried out using optical and scanning electron microscopy, and phase identification was obtained using X-ray diffraction. Vickers hardness, wear and corrosion weight loss tests were used to evaluate the mechanical properties and corrosion behaviour. The results of X-ray diffraction analysis revealed the presence of superhard phases such as FeB, Fe2B, CrB, MnB and MnB2, indicating that pack boriding surface treatment conducted at 1223 K for 8 h exhibited the highest hardness, low coefficient of friction and the greatest wear resistance. Boronitrocarburising treatment, on the other hand, caused a reduction in both the depth of iron borides zone and mechanical properties compared to the boriding surface treatment. These recommended treatments offer to industrialists a particular contribution and interest in the development of these steels, which can be applied in various fields.

Résumé: In the present work, Diamond-Like Carbon (DLC) films were deposited by the Microwave Electron Cyclotron Resonance/Plasma-Assisted Chemical Vapour Deposition process on 41Cr–Al–Mo7 nitrided steel using a benzene–argon gas mixture. The quality of DLC films grown on nitrided steel using different deposit conditions such as benzene flow rate, temperature and time was investigated. Microstructural analysis by Raman spectroscopy showed main G-band peaks are localised between 1564 and 1595 cm⁻¹, while the D-band peaks are centred at 1297 cm⁻¹. Fourier Transform Infrared Spectroscopy showed the peaks attributed to C–H bending and stretching vibration modes are in the range of 2600–3100 cm⁻¹. The microstructure, surface morphology and mechanical properties of the films were examined by X-ray diffraction, atomic force microscopy and use of a Vickers indenter (Zwick). The deposition parameters of the coatings have been studied and optimised to improve mechanical properties. The observed increase in adhesion is related to the formation of (Fe,Cr)3C, Cr3C2 and Cr23C6 interlayer phases. DLC films showed a better wear resistance, higher hardness and low friction coefficient compared to nitrided layers tested for comparison.

Résumé: The main objective of the die heat treatment is to enhance the surface hardness and wear properties to extend the die service life. In this paper, a series of heat treatment experiments were conducted under different atmospheric conditions and length of treatment. Four austenitization atmospheric conditions were studied and although each heat treatment condition resulted in a different hardness profile, it did not affect the results for gas nitriding. All samples subjected to the nitriding process produced similar thicknesses of hardened case layer with average hardness of 70 - 72 HRC if the initial carbon content is not too low. It was shown that heat treatment without atmospheric control results in a lower hardness on the surface since the material was subjected to decarburization effect. The stainless steel foil wrapping around the sample and heat treatment in a vacuum furnace could restrict the decarburization process, while pack carburization heat treatment resulted in a carburization effect on the material.

Résumé: Thermal spraying coatings are used to meet the most stringent industrial requirements in the wider of application. The molybdenum coatings present a good wear resistance which used several mechanical applications. In this work, we studied the mechanical properties of molybdenum coating deposited using thermal flame spraying on gray cast iron with lamellar graphite. After optimization of the spraying parameters, the microstructure was investigated using optical microscopy, scanning electron microscopy and X-ray diffraction. The mechanical properties obtained by microhardness and nanoindentation tests were evaluated on a polished cross section. The mass loss was measured using the abrasive wear test at varying the normal load. The results showed an improvement the mechanical properties of gray cast iron after deposition of molybdenum with wire-flame spraying.