Publication: Evaluación de factores clave para la sinterización con fase líquida de aceros a través de estudios de mojado e infiltración en el sistema Fe-Cu-C
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2012-10
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2012-10-31
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Abstract
A lo largo de las últimas décadas, la pulvimetalurgia ha ido cobrando cada vez más importancia como tecnología de fabricación. No sólo se ha establecido como una alternativa viable a otras tecnologías por su ahorro en materias primas o su flexibilidad para crear piezas de gran complejidad, sino que existen algunos tipos de productos que sólo pueden ser fabricados mediante procesos pulvimetalúrgicos. Su gran potencial radica en que permite controlar en gran medida las características micro y macroscópicas del producto final, tales como el tamaño de grano, la microestructura, la porosidad, etc.; lo cual repercute directamente en las propiedades finales del producto. Se tiende a tratar de conseguir materiales con propiedades diseñadas "a medida" para cada aplicación. Pero para poder llegar a ese objetivo, la industria necesita comprender el funcionamiento de cada una de las etapas del proceso, siendo la sinterización uno de sus pilares fundamentales. Concretamente, este trabajo está enfocado a establecer un primer marco de referencia que permita sistematizar el estudio de los factores que afectan a la sinterización con fase líquida y así poder predecir el comportamiento de futuros sistemas de sinterización. Para ello, se han tomado dos sistemas ampliamente conocidos y empleados en pulvimetalurgia: el Fe-Cu y el Fe-C-Cu; y se ha estudiado, por un lado, la evolución en el tiempo del ángulo de contacto del Cu bajo distintas atmósferas mediante la técnica de la gota sésil, y por otro, el comportamiento a infiltración del Cu en sustratos en verde. En el primer estudio se tuvieron en cuenta tres factores clave para el desarrollo del ángulo de contacto: el tipo de atmósfera, la cantidad de C presente en el sustrato, y la porosidad. Se realizaron experimentos similares sobre sustratos no pulvimetalúrgicos cuya porosidad fuera despreciable, para establecer analogías entre ambos e identificar los posibles puntos en común y de divergencia entre sistemas. Por su parte, con el estudio de infiltración se analizaron las diferentes etapas que sigue el Cu al introducirse en la red de poros del sustrato en verde y cómo éstas están influenciadas por la presencia de C. Para ello se trató de emular el comportamiento de un sustrato real, de una forma tal que se pudiera medir la evolución del infiltrado. Esto se consiguió observando la evolución de la altura normalizada de una gota sésil sobre el sustrato en verde. En ambos experimentos se ha observado la importancia del efecto reductor de la atmósfera y del contenido de C sobre el ángulo de mojado, así como la influencia de este elemento en el proceso de mojado por su efecto sobre la solubilidad entre fases. Finalmente, se ha podido comprobar que, pese al efecto disruptor de la porosidad en el proceso de mojado, el comportamiento entre sustratos densos y porosos es similar, si bien es cierto que el efecto de la porosidad no suele ser despreciable. _______________________________________________________________________________________________________________________
During recent decades, powder metallurgy has gradually become more and more important as manufacturing technology. It has been established as a viable alternative to other technologies. This is due to its savings in raw materials, its high flexibility to create complex shapes and because there are several products that can only be manufactured using this process. Its greatest potential lies in the fact that this technology allows a high level of control over micro and macroscopic features of the final product. Control over variables such as grain size, microstructure or porosity influences directly on the desired behavior of the product and the current trend is to try to design materials with tailor made features for each purpose. However, to achieve this goal, the industry needs to fully understand the particulars of each stage of the process, being sintering one of the main pillars of this process. The scope of this work is to establish a first reference framework to allow a systematization of the study of influence factors in liquid phase sintering, in order to be able to forecast the behavior of future sintering systems. For this purpose, two systems have been chosen: Fe-Cu and Fe-C-Cu. Both are widely known and used in powder metallurgy. The evolution with the time of the Cu contact angle under different atmospheres by means of the sessile drop technique has been studied. The infiltration behavior of Cu on green substrates has been studied as well. In the first study, three key factors for the contact angle development were taken into account, namely, the atmosphere, the amount of C present in the substrate and the porosity. Similar experiments were conducted on substrates with negligible porosity. Results from both experiments were compared to identify similarities and differences. The aim of the infiltration experiment was to understand the different stages followed by molten Cu when it infiltrates through the substrate's pore network, and how these stages are influenced by the presence of C. Consequently, it was necessary to emulate the behavior of a real substrate in a way that it was possible to measure the infiltration evolution. This was accomplished by monitoring the normalized height of a sessile drop while infiltrating into a green compact of the chosen substrate. Both experiments showed the importance of the effect of the atmosphere and the C content on the wetting angle. It has also been shown the influence of C in the wetting process due to its effect on solubility between phases. Finally, it was shown that, in spite of the disrupting effect of porosity in the wetting process, dense and porous substrates behavior is similar. However, it is also true that the effect of porosity is not usually negligible.
During recent decades, powder metallurgy has gradually become more and more important as manufacturing technology. It has been established as a viable alternative to other technologies. This is due to its savings in raw materials, its high flexibility to create complex shapes and because there are several products that can only be manufactured using this process. Its greatest potential lies in the fact that this technology allows a high level of control over micro and macroscopic features of the final product. Control over variables such as grain size, microstructure or porosity influences directly on the desired behavior of the product and the current trend is to try to design materials with tailor made features for each purpose. However, to achieve this goal, the industry needs to fully understand the particulars of each stage of the process, being sintering one of the main pillars of this process. The scope of this work is to establish a first reference framework to allow a systematization of the study of influence factors in liquid phase sintering, in order to be able to forecast the behavior of future sintering systems. For this purpose, two systems have been chosen: Fe-Cu and Fe-C-Cu. Both are widely known and used in powder metallurgy. The evolution with the time of the Cu contact angle under different atmospheres by means of the sessile drop technique has been studied. The infiltration behavior of Cu on green substrates has been studied as well. In the first study, three key factors for the contact angle development were taken into account, namely, the atmosphere, the amount of C present in the substrate and the porosity. Similar experiments were conducted on substrates with negligible porosity. Results from both experiments were compared to identify similarities and differences. The aim of the infiltration experiment was to understand the different stages followed by molten Cu when it infiltrates through the substrate's pore network, and how these stages are influenced by the presence of C. Consequently, it was necessary to emulate the behavior of a real substrate in a way that it was possible to measure the infiltration evolution. This was accomplished by monitoring the normalized height of a sessile drop while infiltrating into a green compact of the chosen substrate. Both experiments showed the importance of the effect of the atmosphere and the C content on the wetting angle. It has also been shown the influence of C in the wetting process due to its effect on solubility between phases. Finally, it was shown that, in spite of the disrupting effect of porosity in the wetting process, dense and porous substrates behavior is similar. However, it is also true that the effect of porosity is not usually negligible.
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Keywords
Pulvimetalurgia, Sinterización, Aceros sinterizados, Ensayo de materiales