Browsing by Author "Celentano, D."

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    Effect of microstructure on thermoelastic stresses in Al2O3/Ti(C,N,O)/Ti (C,N) coating systems studied by Finite Element Method simulations
    (2021) Espinoza, C.; Ramos-Moore, E.; Celentano, D.
    Finite Element Method (FEM) simulations were performed to qualitatively study the effects of texture anisotropy, bonding interlayer thickness, and average crack spacing on the evolution of thermoelastic stress in coatings systems containing Al2O3 and Ti(C,N) layers bonded with a Ti(C,N,O) interlayer. Commercial WC-Co tools were considered as substrates, including a superficial gamma-free phase. Significant stress differences are observed between the Al2O3 and Ti(C,N) layers due to differences in the Coefficient of Thermal Expansion (CTE) relative to the substrate. No significant differences were observed when considering axis-dependent CTE and elastic data of the Al2O3 layer, nor introducing a Ti(C,N,O) interlayer. Cracks across the coatings resulted in a significant reduction of stress in both layers, reaching values near zero in the cracks' vicinity, this effect being more prominent for shorter crack distances. Differences among our FEM simulations and experimental residual stress reports on similar systems highlight the need to develop more complex models to understand the effect of nucleation processes and microstructure on the residual stress. (C) 2021 Elsevier B.V. All rights reserved.
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    Friction characterization when combining laser surface texturing and graphite-based lubricants
    (ELSEVIER, 2020) Martinez Krahmer, D.; Sanchez Egea, A. J.; Celentano, D.; Martynenko, V; Cruchaga, M.
    The present work analyzes the friction capabilities at room temperature of three types of lubricants (denoted as A, B and C) with a graphite concentration of 5%. To do that, the standard pin -on disc test is deployed to study the variation of the friction coefficient when combining these graphite-based lubricants with surfaces made by grinding and different laser surface textures. These lubricants are characterized by measuring the percent of the chemical elements, the average size of the graphite particles and the kinematic viscosity. The experiments show that the lubricant B combined with a higher density of LST presents the lowest friction coefficient of about 0.24. Additionally, assuming a hydrodynamic regime for the textured surfaces, the fluid dynamics simulations carried out as part of the study showed, in agreement with the experimental measurements, the lowest friction coefficient value for a textured surface with the highest dimple density. This seems to be associated to the combined effect of an increase of the hydrodynamic pressure with a weak vortex formation within the dimples, due to the low distortion of the streamlines which, ultimately, attenuates the friction coefficient between the surfaces. (C) 2019 The Authors. Published by Elsevier B.V.
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    Sensitization of AISI 302 stainless steel during low-power laser forming
    (ELSEVIER SCI LTD, 2010) Walczak, M.; Ramos Grez, J.; Celentano, D.; Lima, E. B. F.
    Low-power laser forming by raster scanning is a promising technology for shaping thin sheets in a non-contact manner, using a laser beam scanned over the surface. In this work, the change of material microstructure and the related corrosion behavior are investigated in the context of local temperature evolution during the scanning action. Graphite coated AISI 302 stainless steel coupons have been bent to different angles using a 60 W CO2 laser and the resulting cyclic polarization behavior in sulfuric acid was measured. The so revealed sensitization of the material is discussed on the basis of microstructural changes caused by temperature-induced phase transformations. The total times of permanence at temperatures favoring specific transformations were obtained by numerical simulation of the process. It was found that even when no surface melting takes place the recurrent rise of temperature within the material is sufficient to sensitize the non-irradiated side. This effect might be a limiting factor in applications of laser formed AISI 302 in corrosive environments. (c) 2010 Elsevier Ltd. All rights reserved.