Michel Lambertin

Applications de revêtements durs (CrxNy) obtenus par méthodes P.V.D. à l'usinage du bois

Chromium nitride coatings obtained by triode and magnetron sputtering were applied in peeling and routing process. The efficiency of triode sputtered coatings was shown in machining of MDF, that means in hard cutting conditions, and in routing where a 1000 nm thick CrN film permitted to machine 9 times more than an un-coated carbide tool. Nevertheless, one of the limiting factor we must improve is the adhesion of the coatings on the cutting tools. That is why we also tested magnetron sputtered coatings compared to duplex treatments (nitridation+magnetron coating) in peeling of wood. In view to improve the adhesion of coatings on carbide tools, multilayers such as Cr+CrxNy were also tested as well as polished and coated carbides. While the duplex treatments showed better performances than the monolayers, grinding does not seem to be the solution to improve the adhesion of coatings on carbides.

Development in laser cutting of steel: analytical modeling and experimental validation of the metallurgical effects

The present work reports on the analytical model describing the HAZ geometry near the cut edges resulting from laser cutting of steels induced by the heat flow during the moving of the molten layer in the kerf. This model is based on the molten layer thickness, in macroscopic state, which depends on mean melt velocity and mass balance between mass loss and gain. The energy balance which describes the equilibrium set up in the molten layer is presented and analyzed. Results yield average value for the temperature of molten layer surface and mean melt viscosity. This model indicates that there is a strong dependence between the geometry of the HAZ and the molten layer features. Investigation of the influence of experimental parameters is also performed. Calculated results are compared with experimental measurements.

The Nitridation, A Way To Improve High Temperature Oxidation Behaviour Of AISI 304

The present study focuses on the high temperature oxidation of a AISI 304 chromiaforming nitrided alloy. Isothermal oxidations were performed in air, at 800°C. The effect of nitridation on the steel surface depends on the temperature of the treatment. It leads whether to a γN solid solution formation or to CrN formation. In situ X-ray diffraction has been used to follow the oxides formation. Results show the concomitant growth of CrN and Fe2O3 at the beginning of the test. Then, Cr2O3 quickly appears which leads to the formation of a protective oxide scale (a parabolic rate law is observed). Our conclusions suggest that nitridation increases the high temperature oxidation resistance of 304 steels at 800°C.

Ageing and overageing of lead–calcium alloys

Lead–calcium alloys are commonly used for their high mechanical properties, compared with pure lead. These alloys evolve quickly at room temperature and could in a few months, or years, undergo a softening (overageing). During the last decade, much research has been carried out on the subject without any unanimous results, due mainly to the diversity of the alloys transformations and the difficulties of observation (wide range of kinetics, heterogeneity of transformations, etc.). The use of several in situ techniques developed specifically for lead alloys in our laboratories has enabled us to identify five transformations in lead–calcium alloys. The structural hardening begins by two discontinuous transformations. The first one is complete and the second one of ordering type remains incomplete. The end of the hardening is due to a thin precipitation of Pb3Ca, which is followed by a coarsening (softening) of macroprecipitates aligned in strings. The last softening stage comes with the formation of lamellar Pb3Ca precipitates by coalescence of the macroprecipitates.