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Low carbon steel with carbon content ranging from 0.15% to 0.3% cannot be hardened through quenching and tempering processes and there is little to no martensitic transformation occurring upon quenching. To improve the surface hardness, carburizing is commonly employed. Through this treatment, the surface composition of the low-carbon steel is altered by the diffusion of carbon, resulting in a hard outer casing with good wear resistance. This work investigates the effect of the carburizing treatment temperature and holding time on the crystallographic structure, hardness, and hardened surface layer dimension of commercial low-carbon steel 16NC6. The steel was carburized at 900°C for different holding times of 1, 2, and 3 hours. After the carburizing and quenching processes, the hardness values and the morphology of the crystallographic structure were measured and characterized.

Hard coatings based on chromium carbides and chromium borides are widely used in applications that require mechanical performance, i.e., high hardness and low friction coefficient and good corrosion resistance. In this work, we made layers of chromium carbides and chromium borides on the surface of low carbon steel through some specific treatments. For chromium carbides, the cementation in a solid medium followed by electroplating of chromium on the surface and finally the application of annealing treatment at temperatures between 500 and 1100 °C for 1 hour. For chromium borides, the boriding treatment in solid medium at 900 °C for 4 hours followed by chromium electroplating on the steel surface and finally the application of annealing treatment at temperatures at 950 °C for 1 and 2 hours. The obtained results show that, in the first case, the cemented layer and the chromium deposited on the surface combine to form chromium carbides on the treated surface after annealing. Similarly, for the second case, boron diffusion and chromium deposition lead to chromium borides on the treated surface. The characteristics of the chromium carbides and chromium borides obtained are very similar to those of chromium carbides and chromium borides obtained by other processes.

Steel substrates low carbons were face-hardened by cementing in case, and then thin layers of chromium were deposited by electrolytic way on these substrates. After deposition, the samples were exposed to isothermal annealing in the temperature of 950°C. The characterization of the thin layers was made by means of optical microscopy and interferometry Vickers micro-hardness. From the obtained results, we have established the kinetics of phase shift (under effect the layer of cementing) in the thin layers of chromium which are transformed into chromium carbide while passing by metastable phases of transition. These transformations occurred by diffusion of the carbon atoms coming from layer of cementing, germination and growth in solid phase. This fact has examined according to the temperature of annealing, the evolution of the lattice parameter and the morphology of the deposited chromium layer. As regards the mechanical properties, it was established that the micro-hardness believes with the evolution of the phase shift.

Low carbon steel substrates were face-hardened by cementing, after which thin layers of chromium were deposited electrolytically on these substrates. After deposition, the samples were exposed to isothermal annealing at a temperature of 950°C. The characterization of the thin layers was carried out by means of optical microscopy and interferometry using the Vickers microhardness test. The obtained results allowed establishing the phase shift kinetics (under the effect of the cementing layer) in thin layers of chromium, which are transformed into chromium carbide when passing through metastable transition phases. These transformations were due to diffusion of the carbon atoms coming from the layer of cementing, germination and growth in solid phase. This fact has been examined taking into account the annealing temperature, the lattice parameter evolution and the deposited chromium layer morphology. As to mechanical properties, it was established that the micro-hardness depends on the phase shift evolution

The present study has been conducted in order to obtain titanium carbide layer using a conversion treatment consisting of two main steps. In the first step a thin pure titanium layer was deposited onto 120C4 carbon steel by PVD. In a second step, a vacuum annealing treatment is conducted in order to diffuse the carbon atoms from the substrate toward the titanium coating. As a result, the pure titanium coating is transformed into titanium carbide. However, depending on the annealing temperature, partial or complete conversion into TiC is obtained. Due to that the hardness of the layer depends on the annealing temperature. By a systematic study of the hardness-load variation, the process of the phase transformation of the layer is then confirmed.

International audience; For an accurate determination of the materials hardness, instrumented indentation test is undoubtedly the most adequate technique compared to the classical one. However, numerous laboratories or industries have no access to such instrumented device. Consequently, they have no other alternative methods that the use of classical indentation test. However, this technique can lead to wrong interpretation because it does not allow considering the indenter tip defect.In this paper, we suggest to introduce the indenter tip defect into the classical hardness calculation. The proposed methodology is validated on a diamond like-carbon thin film deposited onto a tungsten carbide. Firstly, the truncated indenter tip defect length is estimated from the indentation size effect observed for the substrates which is attributed to the influence of the indenter tip defect. As a result, the tip defect is found to have the same value independently of the tested samples. Afterwards, the tip defect length is introduced into the composite hardness computation and the model of Jönsson and Hogmark is applied to predict film hardness. As a main result, the film hardness is found equal to 37.3 GPa independently of the film thickness and in a good accordance with literature data regarding the diamond hybridization sp3/sp2 ratio.

The surface areas of the parts subjected to mechanical loads influence to a great extent the resistance to wear and fatigue. In majority of cases, producing of a hard superficial layer on a tough substrate is conducive to an increased resistance to mechanical wear and fatigue. Cementation treatment of low alloy steels which bonds superficial martensitic layer of high hardness and lateral compressive to a core of lower hardness and greater toughness is an example of a good solution of the problem. The high hardness of the martensitic layer is due to an increased concentration of interstitial carbon atoms in the austenite before quenching. The lower hardness of the core after quenching is due to the presence of ferrite and pearlite components which appear if the cooling rate after austenitization becomes lower than the critical on. The objective of the present study was to obtain a cemented surface layer on low alloy steel by means of pack carburizing treatment. Different steel grades, austenitization temperatures as well as different soaking times were used as parameters of the pack carburizing treatment. During this treatment, carbon atoms from the pack powder diffuse toward the steels surface and form compounds of iron carbides. The effect of carburizing parameters on the transformation rate of low carbon surface layer of the low alloy steel to the cemented one was investigated by several analytical techniques.

Microhardness measurements of thin films have to face the problem of the influence of the substrate on the measurement. Numerous models which take into account this behaviour are available in the literature. When the film is composed of several layers of different properties, it is more difficult to solve this problem because of the multiple influences of the different layers and the substrate. Little work on this subject has been already done; we propose here an extension to multilayers of two models: that of Jonsson and Hogmark, based on the relative deformed areas under the indent, and a model we have developed on the basis of plastically deformed volumes in the substrate and in the film. Starting from the hardness determination of Ti and TiC monolayer films, it is shown that it is possible to use either one or the other model to determine the composite superficial hardness of multilayer Ti–TiC films.

The present study has been conducted in the objective of obtaining chromium carbide layers using a conversion treatment involving three main steps: 1) carburizing treatment in order to increase the amount of carbon atoms at the steel surface, 2) deposition of a pure chromium thin layer using electrolytic method and finally, 3) annealing treatment used for carbon diffusion and carbide formation until complete transformation of chromium layer. Depending on the treatment temperature, partial or complete conversion is obtained as a result of the diffusion process. The role of the annealing temperature on transformation rates of chromium into chromium carbide films was investigated. It is shown that for 1 h of treatment the layer is totally transformed at 1100 °C. Hardness and adhesion of layers produced were found to increase whatever the annealing treatment even for partial transformation at the lower annealing temperatures.

International audience; Diamond thin films are used to increase significantly the life time and to improve the performance of cutting tools. However, one the most important limitations to their industrial development in the case of severe mechanical conditions is their limited adhesion to the substrate. To improve the adhesion strength of the deposited diamond film on its substrate, several approaches have been suggested in literature with a relative success. For WC-Co substrates, one interesting approach consists in the neutralization of the cobalt element at the surface of the substrate by the use of a chemical agent. This methodology leads to a roughening of the surface that increases the contact area between the film and the substrate as well as the mechanical anchoring at the interface. The objective of the present paper is to study the conditions of substrate preparation as well as the conditions of deposition on the microstructure and hardness of the produced films. Diamond thin films of thickness ~ 1.5 μm were deposited on substrates made of Tungsten carbide-Cobalt submitted to different heating temperatures. The coated systems were characterized by means of physical and mechanical tests. Observations by Raman spectroscopy and scanning electron microscopy analysis confirm the good quality of the obtained diamond films. Hardness results deduced from classical indentation tests have been analyzed by means of models allowing the separation of the substrate influence on the hardness measurement. In these conditions the hardness of the diamond films was found close to 40 GPa thus confirming their excellent mechanical properties.

La zone superficielle est tres souvent la partie d’un composant qui subit les plus fortes contraintes, c’est également cette zone qui est exposee aux frottements et aux attaques chimiques. Les traitements de surface sont largement utilises pour regler les problemes d’usure, d’attaque chimique, de corrosion ou de fatigue. Ce travail concerne la mise au point d’un traitement de conversion de surface par diffusion précipitation. Ce procède de durcissement superficiel permet d’augmenter et d’améliorer les propriétés en surface des matériaux et plus particulièrement celles des outils. Il est propose dans ce travail, de rechercher les conditions d’obtention d’un carbure de chrome connu pour ses propriétés de résistance `a l’usure, `a la corrosion et `a l’oxydation, `a partir d’un traitement réalise en trois étapes : la première étape est une c´cémentation en caisse par le carbone sur deux aciers `a bas carbone : le XC18 et le 16MC5. La deuxième étape consiste `a déposer `a la surface des aciers traités, un film de chrome m´métallique de quelques μm. La troisième ´étape consiste `a maintenir `a haute température les pièces précédemment obtenues pour convertir la surface chromée en carbure par diffusion du carbone de la zone c´cémentée vers la surface chromée afin d’obtenir par précipitation du carbure de chrome. La caractérisation des propriétés m´mécaniques (dureté et module de Young) par nanoindentation des ´échantillons obtenus est réalisée dans ce travail. The superficial zone is very often the part of a component which undergoes the strongest constraints, it is also this zone which is exposed to frictions and the chemical attacks. The surface treatments are largely used to solve the problems of wear, chemical attack, corrosion or fatigue. This work concerns the development of a surface conversion treatment by diffusion precipitation. This process of superficial hardening allows to increase and to improve the superficial properties of materials and more particularly those of the tools. It is proposed in this work, to search the conditions for obtaining a chromium carbide known by these properties of wear, corrosion and oxidation resistance, starting from a treatment carried out in three stages: the first stage is a pack carburizing (pack cementation) by carbon on two low carbon steels: the XC18 and the 16MC5. The second stage, concerns the deposition on the surface of treated steels a metallic chromium film of a few μm. In the third stage the parts previously obtained are heated at high temperature to convert the surface chrome species into carbide by diffusion of carbon from the cemented zone towards surface chrome species to obtain by precipitation of chromium carbide. The characterization of the mechanical properties (hardness and Young modulus) by nanoindentation of the samples obtained is carried out in this work.

One the most important limitations to the industrial use of hard coatings in severe conditions is associated with their limited adhesion to the substrate. A number of research works have been done in various directions in order to improve the adhesion by post treatments such as laser remelting or thermal treatments. The aim of this work is to evaluate the possibility of using the substrate itself as a carbon source, in order to create very adherent hard titanium carbide coatings by means of a diffusion/precipitation process. A film of pure titanium was prepared by magnetron sputtering on a high carbon content steel substrate. Coated samples were then annealed in vacuum for I h at temperature ranging from 500 to 1100 degrees C. It was observed that the film was totally, partially or not transformed into titanium carbide, depending on heat treatment temperature. The transformation of titanium layer in titanium carbide takes place firstly at the interface between the film and the substrate, then it expands through the whole film thickness, toward the outer surface, by diffusion of carbon coming from the substrate. As a result, complete conversion of the titanium film in titanium carbide is obtained when an annealing temperature of 1100 degrees C is used. A higher adhesion, measured by means of a scratch tester, is found for this coating if compared to the one obtained on samples treated at lower temperatures and to other literature data on coatings having similar thickness and composition. (c) 2005 Elsevier B.V. All rights reserved.

La nitruration est un procede thermochimique destine a ameliorer les proprietes chimiques et mecaniques des aciers et des fontes. Les procedes les plus courant sont la nitruration gazeuse, la nitruration en bain de sels et la nitruration ionique par plasma. Cette derniere presente certains avantages par rapport aux deux precedentes, elle est moins polluante, consomme moins d'energie et permet un traitement local. De maniere generale, quel que soit le procede utilise, le processus de nitruration des aciers se caracterise par la diffusion d'azote a partir de la surface vers le coeur du materiau et par la formation d'une couche de combinaison superficielle apres une periode d'incubation. Si le temps du traitement est suffisamment long, on constate un ralentissement de la croissance de la couche de combinaison alors que la diffusion de l'azote se poursuivre vers le coeur de la piece en formant une solution solide d'insertion dans la nitroferrite ou des precipites de nitrures ou de carbonitrures d'elements allies. Pour ce travail et en vue d'ameliorer le comportement mecanique des echantillons, les aciers nitrures ioniquement pour deux taux d'activation ont subi un traitement supplementaire d'implantation d'ions d'azote. La caracterisation, tant du point de vue microstructurale que mecanique, des couches obtenues a partir de la nitruration ionique avec ou sans implantation ionique a ete effectue et les moyens utilises dans cette etude sont la microdurete, diffraction de rayons X, microscopies optique et electronique a balayage.

La presente etude a ete menee dans le but de valoriser le zinc des residus de lixiviation. Pour ce but, nous avons retenu la methode goethite qui presente certains avantages. La concentration d'acide sulfurique, la temperature et le temps de traitement ceux sont les parametres choisis lors de ce travail. L'effet de trois parametres selectionnes sur la dissolution du zinc des residus de lixiviation a ete etudie. Il est demontre que la teneur en zinc augmente avec l'augmentation des valeurs parametriques.