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En los últimos 10 años, las aleaciones cristalinas de Ti-Cu han sido estudiadas intensivamente por sus buenas propiedades mecánicas y protección contra corrosión. Una de las posibilidades para mejorar aún más estas propiedades es fabricar aleaciones de Ti-Cu amorfas. El objetivo del presente trabajo fue fabricar aleaciones amorfas Ti60 Cu40 mediante molienda mecánica (MA). La microestructura y la posible formación de la fase amorfa se caracterizaron mediante granulometría por difracción láser, microscopía electrónica de barrido (SEM), microscopía electrónica de transmisión (TEM) y difracción de rayos X (XRD). La aleación Ti60 Cu40 se obtuvo en estado amorfo después de 60 h de molienda. In the last 10 years, the crystalline alloys of Ti-Cu have been studied intensively for their good mechanical properties and good protection against corrosion. One of the possibilities to further improve these properties is to fabricate amorphous Ti-Cu alloys. The objective of the present work was to prepare amorphous alloys Ti60Cu40 by mechanical alloying (MA). The microstructure and the possible formation of the amorphous phase were characterized by laser diffraction granulometry, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The alloy Ti60Cu40 was obtained in an amorphous state after 60 h of milling. MINECO (España)/FEDER (UE) DPI2015-69550-C2-2-P MINECO (España)/FEDER (UE) DPI2015-69550-C2-1-P

In this paper, the process known as Electrical Resistance Sintering under Pressure is modelled, simulated and validated. This consolidation technique consists of applying a high-intensity electrical current to a metallic powder mass under compression. The Joule efect acts heating and softening the powders at the time that pressure deforms and makes the powder mass to densify. The proposed model is numerically solved by the fnite elements method, taking into account the electrical–thermal–mechanical coupling present in the process. The theoretical predictions are validated with data recorded by sensors installed in the electrical resistance sintering equipment during experiments with iron powders. The reasonable agreement between the theoretical and experimental curves regarding the overall porosity and electrical resistance suggests that the model reproduces the main characteristics of the process. Also, metallographic studies on porosity distribution confrm the model theoretical predictions. Once confrmed the model and simulator efciency, the evolution of the temperature and the porosity felds in the powder mass and in the rest of elements of the system can be predicted. The infuences of the processing parameters (intensity, time and pressure) as well as the die material are also analyzed and discussed. Fondo Europeo de Desarrollo Regional (FEDER) DPI2015- 69550-C2-1-P Ministerio de Educación y Ciencia DPI2015-69550-C2-2-P

This research is focused on the production of aluminum matrix composites (AMCs) reinforced with various percentages of aluminum nitride (AlN). For this purpose, aluminum powder was milled at room temperature for a total time of 5 hours. The percentage of reinforcement is varied by milling under different periods of vacuum followed by ammonia gas flow. X-ray diffraction analysis showed the benefits of using a combined milling atmosphere to form, after the heat treatment of the powder, a higher amount of AlN. Results showed that the period in vacuum determines the greater or lesser capacity to absorb nitrogen during the ammonia gas period. Even using shorter vacuum milling periods, the AlN formed after sintering can be increased. Ministerio de Economía, Comercio y Empresa DPI2015-69550-C2-1-P

The aim of this work is to study the viability of producing, by medium-frequency electrical resistance sintering (MF-ERS), compacts from mechanically alloyed aluminium powders. The MF-ERS process was carried out using different values of current intensity (6, 8, 10 and 11 kA) and dwelling (heating) times (400, 700 and 1000 ms). Results were compared with compacts processed by the conventional cold pressing and sintering route (850 MPa and 650 C-1h). Depending on the processing route different properties were obtained. The final porosity of the MF-ERS compacts (23.6e7%) can be as low, under the tougher tested sintering conditions, as that of the conventionally produced compacts (6%). The compacts obtained by MF-ERS are less ductile, with lower compression strength than that obtained by the conventional route. Furthermore, a similar electrical resistance and higher microhardness can be reached by the MF-ERS process, despite the duration of the consolidation process is only a fraction of that of the conventional process. Fondo Europeo de Desarrollo Regional (FEDER) DPI2015-69550-C2-2-P Ministerio de Economía y Competitividad DPI2015-69550-C2-1-P

In this paper, a phenomenological model to predict the value of the electrical resistance of a compressed metal powder mass is proposed. The model, based on the experimental compressibility and resistivity-porosity curves, is useful in the field of the electrical resistance consolidation. In this area is often required to find out whether a certain mass of powder inside a die of specified inner section, and subjected to a certain compression, reaches a sufficiently small resistance value so that it can be consolidated by electrical means. The model also predicts the electrical resistance value of the powder mass in case of powders with no oxide layers, or after removing them mechanically or electrically by a previous activation process. The model predictions have been successfully validated through direct measurements of electrical resistance in powder aggregates both in as-received state and after electrical activation. Ministerio de Economía y Competitividad y Unión Europea DPI2015-69550-C2-1-P y DPI2015-69550-C2-2-P

Properties of compacts made from aluminium powder, milled under different atmospheres, were evaluated. The duration of all the milling processes was 10 h, although different atmospheres were tested: vacuum, confined ammonia, and vacuum combined with a short-time ammonia gas flow (5 min). Milled powders were consolidated by cold uniaxial pressing and vacuum sintering.The nature and content of the second phases change with the milling atmosphere, allowing the modification of the mechanical properties of the compacts. Results showed that hardness and tensile strength were highly dependent on the milling atmosphere. Milling carried out in vacuum with a short-time ammonia gas flow notably improved compacts’ properties, as compared with 10 h vacuum milling. Hardness increased from 96 to 150 HB, and ultimate tensile strength rose from 247 to 476 MPa. Ministerio de Economía y Competitividad DPI2015-69550-C2-1-P DPI2015-69550-C2-2-P

Aluminum matrix composites (AMCs) reinforced by aluminum nitride were prepared by mechanical alloying followed by a simple press and sintering method. Milling began under vacuum and after a period of between 1 and 4 h, NH3 gas flow (1 cm3/s) was incorporated until the total milling time of 5 h was reached. Results show that in addition to the strain hardening taking place during mechanical alloying, NH3 plays an additional role in powder hardening. Thereby, the properties of the sintered compacts are strongly influenced by the amount of N incorporated into the powders during milling and the subsequent formation of AlN during the consolidation process. The obtained AMC reaches tensile strengths as high as 459 MPa and hardness much higher than that of the as-received aluminum compact. Ministerio de Economía y Competitividad DPI2015-69550-C2-1-P

The nanocrystallisation behaviour and subsequent intermetallics formation of an amorphous Al88-Y4-Ni8 alloy has been studied. A 1 at% of Al or Ni was also substituted by Cu and its effect studied. Differential scanning calorimetry has been used to measure the thermal stability of these amorphous alloys. Transmission electron microscopy showed the smaller size of the nanocrystals obtained during primary crystallisation when Cu is added. Using three-dimensional atom probe, it has been checked that Cu is homogeneously distributed in the amorphous matrix, not contributing to a heterogeneous nucleation around Cu clusters during the formation of nanocrystals. Transmission electron microscopy and X-rays diffraction are used to study the controversial intermetallics occurrence at higher temperatures. The sequence and characteristics of the intermetallics appearing in these alloys were sensitive to the presence of Cu. The evolution of these intermetallics, up to 600 ºC, has been studied. Findings are compared with previous studies. Ministerio de Economía y Competitividad DPI2015-69550-C2-2-P