Publication: Modificación microestructural y optimización de las propiedades mecánicas de una aleación de Cu-Cr-Zr procesada por ECAP a distintas temperaturas
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2013-09
Defense date
2013-11-19
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Abstract
En el presente estudio se ha investigado la microestructura y el comportamiento mecánico de
una aleación precipitable Cu-1,22%Cr-0,7%Zr (% at.) procesada por Extrusión en Canal
Angular Constante (ECAP) a distintas temperaturas. La aleación ha sido procesada tanto en
estado solubilizado como recocido y se ha sometido hasta un máximo de 12 pases,
imponiéndose deformaciones equivalentes entre 2,8 y 8,4. Los estudios microestructurales
mediante Microscopía Electrónica de Barrido y de Transmisión revelaron que con el
procesado se produce una subestructura de granos/subgranos de tamaño 150-200 nm de
diámetro. Además se observó que los recocidos previos o posteriores al procesado conducen a
la precipitación del exceso de soluto, obteniéndose una distribución homogénea de
nano-precipitados.
Se confirmó que el procesado de la aleación y su combinación con los distintos tratamientos
térmicos mejoran considerablemente la resistencia mecánica de la aleación, a la vez que se
reduce la ductilidad. La evolución del comportamiento mecánico de la aleación con las
distintas condiciones de procesado y de recocido ha sido analizada de manera cuantitativa.
Para esto se ha empleado el modelo de Hall-Petch, que permite cuantificar la contribución al
endurecimiento del tamaño de grano y los modelos de Nembach y Orowan que permiten
cuantificar la contribución de los precipitados. Se confirmó que el incremento de la resistencia
mecánica se debe tanto al refinamiento del tamaño de grano, como a la distribución de nanoprecipitados
que se obtiene con los recocidos, y en menor medida a las dislocaciones libres
remanentes en el interior de los granos.
También se han realizado medidas de Poder Termoeléctrico para analizar cambios
microestructurales durante el procesado ECAP. Debido a la sensibilidad de esta técnica a la
cantidad de soluto en solución y a la presencia de defectos microesctructurales introducidos
durante la deformación, se ha podido estimar la variación del contenido de Cr en solución de
la aleación durante la deformación y los recocidos posteriores. ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
In the present study the microstructure and the mechanical behaviour of an age hardenable Cu-1.22%Cr-0.7%Zr alloy processed by Equal Channel Angular Pressing (ECAP) at different temperatures have been investigated. The alloy has been processed in both solutionised and annealed states, up to 12 ECAP passes, imposing equivalents strains between 2.8 and 8.4. The microstructural study, carried out by Scanning and Transmission Electron Microscopy, reveals that ECAP processing produces a grain/subgrain substructure of size 150-200 nm. It was observed that prior and post ECAP processing anneals lead to the precipitation of the excess solute, producing a homogeneous distribution of nano-precipitates. It was confirmed that the combination of ECAP processing with anneals improve the mechanical strength of the alloy considerably but with some loss of ductility. The evolution of the mechanical behaviour of the alloy with the different conditions of processing and anneals has been analyzed quantitatively. The hardening due to the grain refinement was analyzed using the Hall-Petch model, while the contribution of the precipitates was analyzed using the Nembach and the Orowan models. It was confirmed that the hardening of the alloy after ECAP processing and its combination with anneals is largely determined by the degree of grain refinement and the distribution of nano-precipitates and to a lesser extent to the free dislocations remnant inside the grains. Thermoelectric Power measurements have also been made to analyse the microstructural changes occurring during ECAP processing. Due to the sensitivity of these measurements to the solute content and microstructural defects, it was possible to estimate the variation of Cr content in solution of the alloy during ECAP processing and subsequent anneals.
In the present study the microstructure and the mechanical behaviour of an age hardenable Cu-1.22%Cr-0.7%Zr alloy processed by Equal Channel Angular Pressing (ECAP) at different temperatures have been investigated. The alloy has been processed in both solutionised and annealed states, up to 12 ECAP passes, imposing equivalents strains between 2.8 and 8.4. The microstructural study, carried out by Scanning and Transmission Electron Microscopy, reveals that ECAP processing produces a grain/subgrain substructure of size 150-200 nm. It was observed that prior and post ECAP processing anneals lead to the precipitation of the excess solute, producing a homogeneous distribution of nano-precipitates. It was confirmed that the combination of ECAP processing with anneals improve the mechanical strength of the alloy considerably but with some loss of ductility. The evolution of the mechanical behaviour of the alloy with the different conditions of processing and anneals has been analyzed quantitatively. The hardening due to the grain refinement was analyzed using the Hall-Petch model, while the contribution of the precipitates was analyzed using the Nembach and the Orowan models. It was confirmed that the hardening of the alloy after ECAP processing and its combination with anneals is largely determined by the degree of grain refinement and the distribution of nano-precipitates and to a lesser extent to the free dislocations remnant inside the grains. Thermoelectric Power measurements have also been made to analyse the microstructural changes occurring during ECAP processing. Due to the sensitivity of these measurements to the solute content and microstructural defects, it was possible to estimate the variation of Cr content in solution of the alloy during ECAP processing and subsequent anneals.
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Aleaciones, Propiedades de los materiales, Propiedades mecánicas, Industria metalúrgica