Publication: Producción, procesado y caracterización de aleaciones de Ti de grano fino
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2010-07
Defense date
2010-12-01
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Abstract
La presente tesis trata del desarrollo de nuevas aleaciones de Ti que por su comportamiento mecánico, resistencia a la oxidación, estabilidad térmica o características multifuncionales pudieran sustituir con ventaja a algunas de las aleaciones comerciales de Ti, o extender el rango de aplicaciones de las aleaciones de Ti. Como aleación de tipo α que pudiera tener un buen comportamiento mecánico a altas temperaturas y una buena resistencia a la oxidación se ha investigado la aleación Ti-0,6wt%Y₂O₃. Como aleaciones estables de tipo β con posibilidad de adquirir características multifuncionales mediante deformación plástica severa se han investigado aleaciones de Ti-Nb-Ta-Zr-(V) de diferentes composiciones. Ambas aleaciones se han fabricado mediante técnicas de pulvimetalurgia (P/M) consistentes en una fase de mezclado y aleado mecánico, seguida de compactación en frío, sinterización en alto vacío y un tratamiento final de compresión isostática a alta temperatura y presión (HIP: Hot Isostatic Pressing). Las aleaciones de Ti-Nb-Ta-Zr también se fabricaron mediante fundición y colada. Se ha desarrollado y optimizado el método de preparación de estas aleaciones, investigando el efecto de las condiciones del aleado mecánico, de sinterización y del tratamiento final de HIP sobre la microestructura, composición y propiedades de las aleaciones obtenidas. Las aleaciones se han sometido a diferentes tratamientos térmicos y termomecánicos: forjado, templado y extrusión angular de sección constante (ECAP: Equal Channel Angular Pressing), con el objeto de optimizar su microestructura y propiedades mecánicas. Estas aleaciones, que son consideradas como difíciles de procesar mediante ECAP, han requerido la investigación de las condiciones específicas para realizar con éxito su procesado ECAP. La microestructura de las aleaciones en las distintas etapas de su procesado se analizó mediante diferentes técnicas: difracción de rayos X, metalografía, y microscopía electrónica de barrido y de transmisión. Además, se investigó la textura inducida por el procesado ECAP. La caracterización mecánica se realizó mediante medidas del módulo de Young, microdureza y ensayos de tracción hasta fractura a diferentes temperaturas. Las características de la fractura de estas aleaciones también se investigaron. Además, las características de la oxidación de las aleaciones de Ti-0,6wt%Y₂O₃ y de Ti P/M entre 973 y 1173 K se han investigado mediante termogravimetría y microscopia electrónica de barrido.-------------------------------------------------------------------------------------------------------------------------------------------------------
The present PhD thesis is about the development of new Ti-based alloys that, by virtue of their mechanical behaviour, resistance to oxidation, thermal stability or multifunctional characteristics could extend their field of application or substitute advantageously the actual commercial Ti alloys. In the α range the focus was set on Ti-0,6wt%Y₂O₃, alloy which should have a good mechanical behaviour at high temperatures and a good oxidation resistance. In the β range the investigation was focused on different Ti-Nb-Ta-Zr-(V) alloys with enhanced mechanical properties and possible multifunctional characteristics obtained through severe plastic deformation. Both alloys were produced by powder metallurgy (P/M) techniques consisting in a phase of blending and mechanical alloying, followed by compaction by cold isostatic pressing (CIP), high vacuum sintering and a final hot isostatic pressing (HIP) treatment. The Ti-Nb-Ta-Zr alloys were also prepared by casting. The preparation methods for these alloys were optimized by investigating the effect of the milling, sintering and HIP-treatment conditions on the microstructure, composition and properties of the materials produced. The alloys were subjected to different thermal and thermomechanical treatments: forging, quenching and equal channel angular pressing (ECAP), to enhance their microstructure and mechanical properties. With this objective and to avoid failure of the billets during the ECAP, specific process conditions for these alloys have been investigated. The microstructure of the alloys in the course of the successive processing stages was analysed using the techniques of X-ray diffraction, metallography and scanning and transmission electron microscopy. The crystallographic texture induced by the ECAP process was also investigated. The mechanical properties were determined by Young modulus and microhardness measurements and tensile tests up to fracture at different temperatures. The fracture characteristics of the alloys were also analysed. The oxidation resistance of the Ti-0,6wt%Y₂O₃ and of P/M Ti was also investigated by thermogravimetry and scanning electron microscopy.
The present PhD thesis is about the development of new Ti-based alloys that, by virtue of their mechanical behaviour, resistance to oxidation, thermal stability or multifunctional characteristics could extend their field of application or substitute advantageously the actual commercial Ti alloys. In the α range the focus was set on Ti-0,6wt%Y₂O₃, alloy which should have a good mechanical behaviour at high temperatures and a good oxidation resistance. In the β range the investigation was focused on different Ti-Nb-Ta-Zr-(V) alloys with enhanced mechanical properties and possible multifunctional characteristics obtained through severe plastic deformation. Both alloys were produced by powder metallurgy (P/M) techniques consisting in a phase of blending and mechanical alloying, followed by compaction by cold isostatic pressing (CIP), high vacuum sintering and a final hot isostatic pressing (HIP) treatment. The Ti-Nb-Ta-Zr alloys were also prepared by casting. The preparation methods for these alloys were optimized by investigating the effect of the milling, sintering and HIP-treatment conditions on the microstructure, composition and properties of the materials produced. The alloys were subjected to different thermal and thermomechanical treatments: forging, quenching and equal channel angular pressing (ECAP), to enhance their microstructure and mechanical properties. With this objective and to avoid failure of the billets during the ECAP, specific process conditions for these alloys have been investigated. The microstructure of the alloys in the course of the successive processing stages was analysed using the techniques of X-ray diffraction, metallography and scanning and transmission electron microscopy. The crystallographic texture induced by the ECAP process was also investigated. The mechanical properties were determined by Young modulus and microhardness measurements and tensile tests up to fracture at different temperatures. The fracture characteristics of the alloys were also analysed. The oxidation resistance of the Ti-0,6wt%Y₂O₃ and of P/M Ti was also investigated by thermogravimetry and scanning electron microscopy.
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Keywords
Ensayo de materiales, Aelaciones de Ti, Pulvimetalurgia, Titanio