METALLURGY

Author: RODRIGO HERRERO PILAR.
Year: 2004.
University: REY JUAN CARLOS [www.urjc.es].
Place of defense: ESCUELA SUPERIOR DE CIENCIAS EXPERIMENTALES Y TECNOLOGÍA.
Place of preparation: ESCUELA SUPERIOR DE CIENCIAS EXPERIMENTALES Y TECNOLOGÍA.

Summary: The memory has focused on the study of the influence of the kind of reinforcement and the state of the matrix-matrix composites reinforced with aluminum discontinuous (dras) on their behavior micromecánico and against corrosion in aggressive ways. For this, two materials have been used by commercial manufactured via pulvimetalúrgica constituted by the same parent aa2009. This is an alloy ai-cu-mg developed exclusively for the manufacture of dras for aerospace use, and that is characterized by a very low percentage of impurities. This matrix in each of the compounds studied material is reinforced with 15% of silicon carbide subject to various morfologías: in the form of particles, AA2009/SIC/15P, in the form of whiskers, AA2009/SIC/15W. By microstructural characterization techniques, such as optical microscopy, electron microscopy, diffraction and x-ray fluorescence, were studied starting materials to determine the morphology and grain size, the states of precipitation in the matrix, the size and arrangement of effort within the aluminum alloy, and so on. All these factors will influence the subsequent behavior of the material in service and also their response to various heat treatments. The second step was to study the kinetics of precipitation and sequences of the matrix. Once characterized the materials were subjected to heat treatment T6 and T4 and through measures hardness and microdureza vickers is avaluó hardening capacity depending on the means of tempering, the temperature of maturation and the morphology of reinforcement. This study was completed tests with differential scanning calorimetry (DSE) to determine the sequence and precipitation kinetics of the alloy. Thanks to the transmission electron microscopy (TEM) was able to identify the different phases that are formed during the aging of the materials. Subsequently tensile tests were conducted on samples treated and untreated groups to check the influence of both the morphology of strengthening the rule of precipitation in the matrix material deformation mechanisms that control the judgment of these materials. This could be carried out thanks to the use of miscroscopia electronics, both scan (SEM) and transmission (TEM). Finally, to assess the behavior of materials off the rust corrosion studies were conducted under different conditions. By testing polarization cicllca was studied susceptibility to corrosion by bite media clorurados. In this environment it was also felt the speed of corrosion tests by DC. Further tests were carried out in salt spray chamber and climatic chamber. The results showed that these materials are highly susceptible to localized corrosion Check also that the kind of reinforcement and the treatment they are subjected materials are matters to be taken into account.

Author: PINEDA TRIANA YANETH.
Year: 2005.
University: POLITÉCNICA DE VALENCIA [www.upv.es].
Place of defense: INGENIERÍA MECANICA Y DE MATERIALES.
Place of preparation: UNIVERSIDAD POLITÉCNICA DE VALENCIA.

Summary: Stainless steels are widely used in applications where there is a need for good corrosion resistance. However, its mechanical properties such as hardness and abrasion resistance are not always satisfactory. This fact has prompted the study of surface treatment techniques for improving their performance through processes, among which the laser coating. This technique of recent use has become an alternative capable of modifying the surface of the material coated response to specific conditions of service. This is achieved by combining a wide variety of materials that can be used as coating and the substrate on which it is applied, turning the laser coating, a process of high flexibility. This feature enhances the surface condition but also use the technique as a tool for repair and recovery dimensional pieces worn. However, the number of parameters involved in the process, makes it imperative its optimization in order to achieve layers of coating quality. That's why, once selected, and austenitic stainless steel substrate as powders and austenitic stainless steel and martensítico as coating, a detailed study of the influence of some of the process variables, the profile of the deposit. This will vary parameters such as speed table, the flow of powder made and the gas flow protection employee and explores its effect on the coating from geometrical aspects such as height, width, penetration, dilution and the contact angle between it and the substrate, for the two types of lasers used CO2 and Nd: YAG. As the purpose of the study is to achieve recovery dimensional these pieces from laser powder coating of the same kind, it is necessary to evaluate the microstructure of the surface layer achieved. To achieve this, use the use of techniques such as optical microscopy, scanning electron microscopy and transmission diffraction and X-ray Additionally, characterized the microtextura the coating obtained, and particularly the interface between the substrate and coating, using the technique EBSD; diffraction of electrons retrodispersado, which identifies the direction of the grains of the material as a substrate for both coating. The mechanical properties are evaluated from measurements of microdureza practiced in the cross section of coating the substrate and the interface between them. Finally, it evaluates the alternative repair cracks open on the surface by laser powder coating of surface discontinuities simulated with the same techniques used in the mechanical and microstructural characterization, complementing the latter with tensile tests.