Browsing by Author "Ramos Grez, J."

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    A method for manufacturing cellular metals with open- and close-type porosities
    (ELSEVIER SCIENCE BV, 2011) Covaciu, M.; Walczak, M.; Ramos Grez, J.
    New approach for manufacturing metallic cellular materials with controlled open pore geometry and cells arrangement is presented. The method is based on the combination of rapid prototyping of a template with powder metallurgy. Modification of the procedure allows for additional introduction of closed-type porosity with pores smaller than those defined by the rapid prototyped template. The accuracy of the method for controlling the size, shape and arrangement of open-type pores is presented on the example of zinc with an inorganic template (CuSO(4)). The same materials are used to produce a structure with two types of porosities combined in one structure, regular opened and irregular closed. The control of pore geometry allows for optimization of metallic cellular materials for their mechanical, chemical and biological applications. (C) 2011 Elsevier B.V. All rights reserved.
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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.