Influence des post-traitements sur la résistance à l’usure des dépôts en superalliage Ni-Cr-Al-Mo obtenus par projection thermique

Ce travail porte sur la caractérisation microstructurale, structurale et mécanique des dépôts métalliques à base Nickel déposés sous forme de poudres par la technique de projection thermique flamme-poudre sur un substrat type E335. Pour améliorer les propriétés de ces dépôts, des traitements thermiques sont préconisés en vue d’homogénéiser ces derniers et permettre d’obtenir de meilleures propriétés mécaniques. Ces post-traitements ont été réalisés à différentes températures 400, 600 et 800 °C avec un temps de maintien d’une heure et un refroidissement à l’air. La caractérisation structurale et microstructurale de la poudre et des dépôts est obtenue en utilisant le microscope électronique à balayage (MEB) et la diffraction X (DRX). Des relevés de micro duretés Vickers ont été également réalisés sur la surface de ces dépôts. Les essais tribologiques ont été réalisés avec une configuration pion-disque à différentes charges avec deux vitesses de glissement en vue de déterminer le taux d’usure. Les observations microstructurales ont montré que les traitements effectués aux températures de 400 et 600 °C ont réduit les porosités en rendant les microstructures plus homogènes et plus denses par le phénomène de colmatage. Par contre, le traitement à 800 °C a présenté un délaminage au niveau de l’interface substrat/dépôt. Les résultats d’usure ont révélé que la vitesse de glissement et la pression de contact appliquée influent sur la variation du taux d’usure et que les dépôts traités à 400 °C présentent une meilleure résistance à l’usure que ceux traités à 600 et 800 °C

Microstructure and adhesion of 100Cr6 steel coatings thermally sprayed on a 35CrMo4 steel substrate

International audienceThermally sprayed of 100Cr6 steel coatings are widely used to combat degradation of components and structures due to mechanical wear. In this paper, the microstructure and adhesion energy of 100Cr6 steel coatings thermally sprayed on a 35CrMo4 steel substrate are investigated. The microstructure characteristics of the deposits are studied using the combined techniques of X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM) including energy-dispersive spectroscopy (EDS). The practical work of adhesion of flame-sprayed 100Cr6 on steel substrate is determined using a four-point delamination bending test. The influence of a molybdenum bond coat on the adhesion is also studied. Microstructure suggests that the coating is mainly constructed by splats of γ-phase (fcc) and FeO. Phase analysis also confirms that during spraying process, a stable α-phase (bcc) was transformed into a new γ-phase (fcc). The highest values of the fracture energy are obtained for the 35CrMo4 substrate/100Cr6 steel deposit type samples. On the contrary, when a molybdenum bond coat is introduced (composite system 35CrMo4 substrate/Mo bond coat/100Cr6 steel deposit), the fracture energy decreases in a ratio of approximately three. So, the presence of a Mo bond coat as a barrier between the coating and the substrate has a negative role on the adhesion

Microstructure analysis and mechanical characterisation of NiWCrBSi coatings produced by flame spraying

International audienceThis work presents microstructure and mechanical properties of NiWCrBSi coatings produced onto mild steel substrate by oxyacetylene flame spraying, using two different stoichiometries. Coatings were analysed by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and X-ray diffraction. Microhardness tests were carried out using a micro-hardness tester operating with Vickers indenter and the load being 3N. Results showed that both coating microstructures were of lamellar/stratified type, containing several inhomogeneities such as unmelted particles and pores. Coatings consisted mainly of a solid solution (Ni, Cr and Fe), containing two different phases of hexagonal structure, namely WC and Ni 31 Si 12 . The presence of WC hard particles contributed to the high coating hardness. Oxidizing flame conditions showed a potential interest for tribological applications, because of a reduced porosity and an increased coating hardness

Structural, morphological and electrical properties of La1-xSrxAlO3-delta(x=0, 0.1, 0.15) synthesized by the Pechini method

La1-xSrxAlO3-delta (x = 0, 0.1, 0.15) fine particles were prepared by the Pechini process using citric acid and ethylene glycol at low temperature 900 degrees C. The powders were studied by several physical characterization techniques. The FTIR spectrum of the resin treated at 200 degrees C revealed the formation of a metalorganic complex and a polymerized form of ethylene glycol. XRD spectra of the samples, calcined at 900 degrees C, illustrated a single phase LaAlO3. However, La0.9Sr0.1AlO3-delta and La0.85Sr0.15AlO3-delta powders mainly consist of a deficient hexagonal perovskite phase with a small amount of a second phase (LaSrAl3O7). Ionic conductivities of these materials were studied by impedance spectroscopy in the range of 100-700 degrees C in air