ALLOYS

Author: CASTRO BERNAL VANESSA DE.
Year: 2003.
University: CARLOS III DE MADRID [www.uc3m.es].
Place of defense: ESCUELA POLITECNICA SUPERIOR.
Place of preparation: UNIVERSIDAD CARLOS III DE MADRID.

Summary: The aim of the thesis has been to improve the mechanical behavior of titanium by reinforcing particles. This has been achieved composite materials (composites) titanium reinforced TiC (TiB + TiC) or Y2O3 melting in a furnace arc. It has analyzed its microstructure through X-ray techniques, scanning microscopy (SEM) and transmission microscopy (TEM), and their behavior has been investigated in mechanical tension between 298 and 973 K. After the tests, analyzed the microstructure of the composites deformed and related microstructure observed with the mechanical properties obtained. The results show the effect of firming nano particles of Y2O3, at least until 498 K. Particles of TiC and TiB break easily to 298 K, with a higher firming effect at high temperatures. These results have been interpreted on the basis of the models hardening classics. In the case of composites of Y2O3/Ti has analyzed the interaction of dislocations with particles Y2O3. For these composites have also been carried out measures microdureza Vickers and had established a correlation between microdureza and mechanical strength.

Author: ORTEGA VILLAFUERTE YANICET.
Year: 2004.
University: COMPLUTENSE DE MADRID [www.ucm.es].
Place of defense: FACULTAD DE CIENCIAS FÍSICAS.
Place of preparation: FACULTAD DE CIENCIAS FÍSICAS.

Summary: The thesis is a study of the mechanisms that take place in hardening alloys based MgCa and FeAl, the formation of secondary phases and the retention of thermal vacancies, respectively. In all cases using the technique of positron life time and in some experiments included measures Doppler broadening of the line of 511 keV annihilation. To determine the role of zinc in the high levels of hardness of the alloy temaria (MgCaZn), have compared the results of the measures microdureza and the positron annihilation spectroscopy. It has been suggested that the cause of the high rate of hardening in the early stages of the aging process in the alloy MgCaZn, is due to the formation of structures that are consistent nucleation sites of precipitates, which is a consequence of the presence of Zn atoms. Through deformation processes made alloys aging MgCa and MgCaZn has shown the effectiveness of the respective microstructures as barriers to the spread of plastic flow. In terms of alloys based FeAl has studied the effect of the addition of Cr and Si in retaining thermal vacancies created 10000 C. The study was conducted using various heat treatments and hardening annealing and has studied the behavior of dislocations induced in the process of deformation in alloys FeA1Cr.

Author: GARCIA CALDERON REBECA.
Year: 2005.
University: CANTABRIA [www.unican.es].
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: FACULTAD DE CIENCIAS.

Summary: The physical properties of materials have changed when it reduced the sizes of the specimens, especially when the sizes involved fall within the range of nanometers. Thus, the study of the mechanisms involved in these behaviors dependent on the size has resulted in the outbreak of nanoscience and nanotechnology. Within the field of magnetism this has led to interest in magnetic systems heterogeneous. To contribute to the study of magnetic behavior of this type of material has been synthesized by the method of mechanical alloy ternary alloys of Fe-Cu-Ag with different composition of which were selected two Fe13Cu10Ag77 and Fe22Cu14Ag64 as the most suitable for the study of the phenomena associated with the relaxation of magnetic nano particles. Based on a detailed structural characterization of these alloys by obtaining images SuperSTEM, Rietveld refinement package (multipattern) of the results of diffraction Rayos-Xy neutron analysis and dissemination of low-angle neutron (SANS) , it has been concluded that these alloys are made up of magnetic particles of Fe (Cu) in solid solution of 4 ~ 4.6 nm, dispersed in a matrix of Ag diamagnetic. The only significant change between the two alloys is the concentration of these magnetic particles, 18% in volume for Fe13Cu10Ag77 and 29% for Fe22Cu14Ag64. There have also been detected by SANS clusters of particles, that the parks are very close interacciionan heavily behaving To high to low H as a single larger. Based on the results of Mdc (H, T) and Xac (T h, v) and spectroscopy MÃ ¶ ssbauer suggests that interactions exist between particles of Fe (Cu) as a condition of the magnetic relaxation of the system. These interactions are kind dipolar magnetic and increase in value as the growing concentration of particles of the alloy Fe13Cu10AG77 to Fe22Cu14Ag64. Thus, the magnetic behavior is primarily the result of particles nano monodominio although the presence of strong dipolar interactions makes cooperative effects appear similar to those taking place in systems of spin glass type, constituting a state that might be called superparamagnetic correlated (CSPM ). The results obtained using sophisticated techniques and unconventional espectrosopia of muones (uSR) and neutron spin echo (NSE), provides a direct evidence of magnetic relaxation timescale nanoscópica in the absence of magnetic field applied. These results confirm the existence of a behavior CSPM and open a new line of inquiry.

Author: Azpilgain Balerdi Zigor.
Year: 2005.
University: MONDRAGÓN UNIBERTSITATEA [www.mondragon.edu].
Place of defense: Mondragon Goi Eskola Politeknikoa.
Place of preparation: Mondragon Goi Eskola Politeknikoa- Mondragon Unibertsitatea.

Summary: This thesis has developed technology forged aluminum alloys in semisolid state to mass produce components, preferably oriented automotive area. Over the work has been evaluated in accordance semisolid state alloys smelting A356 and A357, the second merger casting alloys of the type 380, and forging alloys of the series 7000. An important part of the investigation has focused on the analysis of the thermodynamic properties of the alloys mentioned, in order to predict, from a theoretical point of view, the formability in semisolid state of the same. Based on this analysis have been raised amendments to the composition of the alloy to improve its formability. The other part of the work has been shaped in the number of aluminum alloys using technology built in semisolid state, for which it has been necessary to develop, and in some cases designed and constructed, all the necessary equipment. All along manufactured piece of work has been analyzed from the perspective of the possible application of the technology for the manufacture of automotive parts sector.

Author: GOICOECHEA MIDDELMANN JÒRGEN.
Year: 2005.
University: BARCELONA [www.ub.es].
Place of defense: FACULTAD DE FÍSICA.
Place of preparation: FACULTAT DE FÍSICA, UNIVERSITAT DE BARCELONA.

Summary: Study of the hysteresis phenomenon and sequencing of target states in stable phase transitions of the first order. To carry out these studies have chosen some theoretical models as ideal representatives of the real systems that have similar characteristics. Introduction to the issue of hysteresis and metaestabilidad in phase transitions of the first order. Studies, results and conclusions: Partition sequential phase transitions of the first order model preisach as a model spin sequence key states in the RFIM AT = 0 with external field energy balance in the RFIM with a dynamic model without fluctuations A 3 states of spin: RFBEG Universality Hysteresis and properties of memory in a cellular automaton deterministic.

Author: IBARRA GALIÁN ALFONSO.
Year: 2005.
University: PAÍS VASCO [www.ehu.es].
Place of defense: FACULTAD DE CIENCIA Y TECNOLOGÍA.
Place of preparation: FACULTAD DE CIENCIA Y TECNOLOGÍA UPV/EHU.

Summary: This doctoral thesis falls within the framework of the shape memory alloys. The whom have a reversible phase transition that gives them some properties termo-mecánicas extremely useful in fields such as medicine or industry aero-espacial. Within these alloys Cu-Al-Ni present enormous advantages over the rest, such as its low cost and ability to work at temperatures close to 200Â ° C. At the same time, samples of this family of polycrystalline alloys are extremely fragile, which dramatically reduces its scope. Therefore, the work done during these four years, and that is reflected in this report now has two fundamental goals: On the one hand knowing the microstructure of the alloys monocristalinas and its evolution as a function of the temperature, as well as mechanisms micrsocópicos controlling for processing, in order to understand as much as this micro-estructura can influence the transformation martensítica as that the transformation can change the microstructure. To achieve this goal have been conducted mechanical tests depending on the temperature, the maximum deformation reaches or number of cycles and the sense of the applied voltage. Measures have also been made by DSC, optical microscopy, scanning and test traction "situ" at the MET. On the other hand seeks reduce the high fragility of the polycrystalline samples. The samples have been characterized by a new technique developed based on powder metallurgy developed within our research group.

Author: CONCUSTELL FARGAS AMADEU.
Year: 2006.
University: AUTÓNOMA DE BARCELONA [www.uab.es].
Place of defense: UNIVERSIDAD AUTONOMA DE BARCELONA.
Place of preparation: FISICA DE MATERIALES 2.

Summary: Since the sixties, metallic glasses have been subjected to a large number of investigations, then ties have made very significant progress in understanding its structure and some of its properties. As its name indicates, metallic glasses are metallic alloys that have no long-range atomic order. This lack of order gives them different properties and behaviors respect to the crystalline alloys and materials. For example, their mechanical properties differ significantly from the crystalline material, and showing a high yield strength, a rise in regime elastic deformation, plastic deformation heterogeneous and homogeneous, and also the emergence of molten material on the fracture surfaces. The combination of a high yield strength along with the possibility of obtaining metallic glasses massifs has opened a renewed interest in using these as structural materials. Still, the metallic glasses show a clear location of the plastic deformation bands in court to be deformed at room temperature. Moreover, instead of experiencing strain hardening, metallic glasses are ablandecen because of the formation of these bands cutting impeding the stable elongation of the material when it is deformed in tension. Thus, improving the ductility of such materials has become the goal of many studies. In this dissertation is to study the fundamentals of the deformation of several families of glass and metal nanocomposite materials from compression tests and nanoindentación. The mechanisms of deformation elastic, inelastic and plastic glasses metal influence the response obtained in experiments nanoindentación in a fundamental way. The comments and discussion carried out in this work helps differentiate the three mechanisms of deformation on the charts obtained on the experiences of nanoindentación made. They also have studied the mechanisms of deformation of different materials nanocomposites:-From-based metallic glasses Cu has been forming an amorphous alloy matrix and a homogenous dispersion of nano-sized crystals. Thus, the crystallization, the thermal stability and mechanical properties of the glass-based system Cu-Zr-Ti have been studied. Based on the knowledge gained has been obtaining a material nanocompuesto causing the primary crystallization of metallic glass above. It has been observed that the amorphous matrix dominates the mechanical properties of the alloy, but the precipitation of a phase intermetallic harden the material. - Tapes have been obtained in the system Ni-Nb-Y consist of two amorphous phases due to immiscibilidad introducing the system Nb-Y both in the solid state and in the liquid. It has been observed that the plastic deformation of this alloy is clearly different from that of a metallic glass monolithic. Thus, its plasticity and toughness can only be explained by the interaction of the bands cutting formed in the matrix and the second phase precipitated in the form globular. - Has been carried out studying the microstructural evolution and mechanisms of hardening after deform plastically by torsion based on Ti alloy composed of a matrix combined with eutectic nanometer dendrites of micrometer size. Before the plastic deformation, the dendrites are tougher that the matrix eutectic already suffering from a hardening by solid solution. After the deflection, both the matrix as dendrites harden, but at different rates up to the same hardness in both phases. The mechanisms of these endurecimientos differ 8 in every 827 phase because of their different nature. The mechanisms of deformation and applications of metallic glasses i nanocomposite materials are still a new field of research. Research conducted during this dissertation have a better understanding of some of the proposed routes for improving the mechanical properties of metallic glasses, and develop nanocomposite materials or phase separation. In addition, the use of complementary techniques such as electron microscopy and transmission tracking, have provided invaluable information to investigate the microscopic mechanisms that govern the plastic deformation in metallic glasses and nanocomposite materials. Also, it is necessary to highlight the use of nanoindentación to study the mechanisms responsible for deformation in metallic glasses, as well as differentiate hardening of the different phases that form a compound. The results presented assist in the interpretation of phenomena such as the effect of size of the indentation, relaxation processes during deformation, deformation and cyclic deformation during the indentation of glass and metal nanocomposite materials. Finally, it should be clear that it is necessary to continue research in these materials in order to optimize their properties and they can be used in technological applications.