The competitiveness of conventional press & sinter technology mainly depends on the ability to obtain tight tolerance on sintered products. In order to maintain this strategic advantage in spite of the rapid global market changes, a continuous improvement in the dimensional accuracy of the products has to be pursued. One of the major limits in the dimensional precision of sintered products regards the anisotropic dimensional change occurring on sintering. Despite this problem is well known, an effective design procedure accounting for the anisotropic behavior of dimensional variations is far to be reached. The main reasons concern the multiphysical mechanisms involved and the effect of material, geometry and process condition on the final results. This work aims at developing a design methodology accounting for the anisotropy of dimensional changes on sintering. This study has been performed considering both the fundamental principles and the industrial application, aiming at proposing: - a solid theory considering the mechanisms which determine the anisotropic dimensional changes; - a practical and effective design tool for the industrial application. The role of uniaxial compaction on the origin of anisotropic dimensional change was firstly investigated. AISI 316L ring shaped samples were compacted at different geometries, and four different particle sizes. During single action compaction, forces acting on the tooling and powder column, and related displacements, were recorded by the press in order to derive the compaction mechanics of the powder mixes. Further, the dimensions of the samples were measured before and after sintering. A linear trend was observed correlating the deviatoric stresses occurring in compaction to the anisotropic dimensional variations on sintering. This result offers a new perspective in the prediction of the anisotropic dimensional change, and could lay the foundation of a solid model. Aiming at developing an effective design tool to predict dimensional change on sintering, the analytical design procedure previously developed by the research group at the University of Trento was validated on real parts. A Club Project was promoted by EPMA, collecting the University of Trento and five qualified industrial partners. These companies provided five different real parts characterized by different materials and geometries, whose dimensions were measured before and after sintering. The comparison of the measured and the predicted sintered dimensions demonstrated that this design approach can be an effective tool for designers. Further work could implement the promising results obtained investigating the compaction mechanics in the design procedure, aiming at defining a powerful tool to design PM parts accounting for anisotropic dimensional changes.

This work aims at improving the previously developed design procedure accounting for anisotropic dimensional changes on sintering. The goal of the project is both enlarging the reference database and investigating in depth the parameters responsible for anisotropic dimensional changes. The effects of green density, geometry, and compaction parameters (compaction speed hold down force and hold down time) on the anisotropy of dimensional changes on sintering were investigated. Ring shaped parts made of eight different iron-based materials were investigated in order to cover a large range of dimensional changes and different sintering mechanisms. The work is divided into two main parts. The first part focuses on investigating the effects of green density and geometry on the anisotropic dimensional changes, also enlarging the database. The application of the design methodology previously developed showed the significant role of anisotropy in the compaction plane for accurate prediction of dimensional changes, which was not highlighted previously. To solve this critical point a new anisotropy parameter is proposed and implemented in the design procedure. With the new anisotropy parameter, prediction of dimensional changes was improved while another critical point was highlighted, which is the scatter in the database. In order to have a reliable design procedure, database must be as accurate as possible, as demonstrated by a careful analysis on data processing. In the second part, the effect of compaction parameters on the anisotropy of dimensional changes on sintering was investigated, with a focus on the anisotropy in the compaction plane highlighted in the first part. No direct correlations were found between anisotropy of dimensional changes and compaction parameters, but compaction settings leading to lower anisotropy in the compaction plane were highlighted. Application of design methodology confirmed that the accuracy of predictions is higher when the sampling is less scattered. Also, a numerical study based on the experimental results was done to evaluate the possibility of neglecting anisotropy in the compaction plane for predicting dimensional changes. It was demonstrated that neglecting anisotropy in the compaction plane is acceptable, for some materials produced using the compaction settings minimizing such anisotropy. Additionally, a correlation between springback during ejection of the parts after compaction and anisotropy in the compaction plane was found.

Introduction. Executive function refers to the top-down neurocognitive processes involved in flexible, goal-oriented behavior. A number of studies have shown positive effects of EF training. The overall aim of these studies was to explore the neurocognitive processes that support the development of EF by understanding how EF training works and what the active ingredients are. Particular interest was in isolating the role of reflection in EF training to understand its top-down affect on ACC-mediated conflict detection. Method. In Exp. 1 the neural markers of EF were explored by comparing ERPs of preschoolers who passed the DCCS and preschoolers who failed. Exp. 2 represents an attempt to replicate the key findings of Kloo & Perner, (2003, Exp. 2) that reflection training improves preschoolers’ performance on the DCCS and demonstrates far transfer. A shortened version of the training protocol was also tested (Exp. 3). In Exp. 4, the neural correlates of reflection training in preschoolers were explored by examining changes in the neural marker of EF found in Exp. 1. Results. In Exp. 1, the N2 amplitude was smaller (less negative) for children who passed the DCCS and were able to efficiently resolve the conflict in the stimuli than for children who failed and were unable to resolve the conflict. Exp. 2 replicated the findings of Kloo & Perner, (2003, Exp. 2) even using a brief (15 min) intervention targeting reflection (Exp. 3). In Exp. 4, one brief session of reflection training made children who initially failed the DCCS look like children who initially passed at both the behavioral and neural level (reduced N2 amplitude). Conclusion. Results suggest that reflective processing facilitates the development of EF in young children by teaching them to notice conflict, reflect on it, and formulate rules for resolving it, resulting in the down-regulation of ACC-mediated conflict detection.

Introduction. Executive function refers to the top-down neurocognitive processes involved in flexible, goal-oriented behavior. A number of studies have shown positive effects of EF training. The overall aim of these studies was to explore the neurocognitive processes that support the development of EF by understanding how EF training works and what the active ingredients are. Particular interest was in isolating the role of reflection in EF training to understand its top-down affect on ACC-mediated conflict detection. Method. In Exp. 1 the neural markers of EF were explored by comparing ERPs of preschoolers who passed the DCCS and preschoolers who failed. Exp. 2 represents an attempt to replicate the key findings of Kloo & Perner, (2003, Exp. 2) that reflection training improves preschoolers’ performance on the DCCS and demonstrates far transfer. A shortened version of the training protocol was also tested (Exp. 3). In Exp. 4, the neural correlates of reflection training in preschoolers were explored by examining changes in the neural marker of EF found in Exp. 1. Results. In Exp. 1, the N2 amplitude was smaller (less negative) for children who passed the DCCS and were able to efficiently resolve the conflict in the stimuli than for children who failed and were unable to resolve the conflict. Exp. 2 replicated the findings of Kloo & Perner, (2003, Exp. 2) even using a brief (15 min) intervention targeting reflection (Exp. 3). In Exp. 4, one brief session of reflection training made children who initially failed the DCCS look like children who initially passed at both the behavioral and neural level (reduced N2 amplitude). Conclusion. Results suggest that reflective processing facilitates the development of EF in young children by teaching them to notice conflict, reflect on it, and formulate rules for resolving it, resulting in the down-regulation of ACC-mediated conflict detection.

This thesis investigates the use of bromine intercalation of graphite as a method to simulate and investigate irradiation damage. In particular this study investigates the effects of intercalation on dimensional change on the macro and micro scales and how these changes combine to affect Young’s modulus. Highly Orientated Pyrolytic Graphite has been used to gather data as a close approximation to single crystal graphite. Three different grades of polycrystalline nuclear graphite have been used to investigate the effect of different microstructure on intercalation and subsequent property changes. The graphites have been characterized by optical microscopy, pycnometry and x-ray powder diffraction and texture measurements. A number of bespoke rigs were designed and manufactured to carry out sorption, tomography and laser vibrometry experiments.The results indicate that the rate of dimensional change for polycrystalline graphites is significantly lower than for single crystal graphites. Modelling of dimensional change suggests that the difference in expansion is due to closure of porosity. Closer investigation of the dimensional change within the microstructure shows that the majority of the dimensional change is driven by expansion of filler particles.The young’s modulus results show an initial increase in modulus followed by a decrease, which corresponds with empirical evidence for irradiated samples. It is postulated that the initial increase in modulus is due to crystal expansion and that the subsequent decrease is due to crack growth. After experimentation some samples show significant cracking which would appear to support this assertion.

One main reason for the use of Fe-Cu-C system in PM industry is the presence of liquid phase (copper) at the start of sintering (1120oC). The diffusion of liquid copper into iron causes swelling in the structure. This in turn can cause high dimensional change and, if not controlled properly, may cause distortion. So it is of paramount importance to control the copper diffusion. Carbon, added as graphite, reduces the swelling of copper by changing the dihedral angle. The affect of graphite on copper diffusion depends on the graphite type, particle size of graphite and heating rate. The aim of this work was to find the influence of graphite type and particle size of graphite on copper diffusion. Water Atomized iron (ASC100.29) produced in Höganäs AB was taken as the base powder.  Two types of graphite were used each with two different particle sizes. Two different graphite quantities (0.2% & 0.8%) for each type was taken. Natural fine graphite (UF4), Natural coarse graphite (PG44), Synthetic fine graphite (F10) and  Synthetic coarse graphite (KS44) were the graphites used in this work. Powders were compacted at 600 Mpa and the sintering was done at 1120oC for 30 minutes in 90/10 N2/H2. Dilatometry and metallographic investigation of the samples sintered in the production furnace were used to understand the graphite influence.   The investigation showed that at low graphite levels (0.2%), the affect of graphite type or graphite size was not significant on copper diffusion. At high graphite levels (0.8%),  synthetic graphites were more effective in reducing the swelling of copper. Influence of  particle size of synthetic graphites on Cu diffusion was not significant compared to the influence of particle size of natural graphite. There was also a considerable affect of heating rate on graphite dissolution and copper swelling.

Les liants ettringitiques dont la composition est formée principalement par du ciment d’aluminate de calcium et par du sulfate de calcium, sont très utilisés dans le cadre des mortiers techniques pour des applications telles que les mortiers de ragréage, les chapes autonivelante, les mortiers de réparation…. en raison de leurs propriétés de durcissement rapide et de résistance initiale élevée. Néanmoins, en fonction de la quantité des matières premières utilisées dans la composition et de leur nature, ces liants peuvent présenter à jeune âge ainsi qu’à long terme, des comportements différents. En particulier et dans le cadre de ce travail, l’influence de la nature et du dosage en sulfate de calcium sur l’hydratation des mortiers ettringitiques comme le début de prise, le changement de l’état liquide à l’état solide, les variations dimensionnelles, la résistance et le vieillissement à long terme (jusqu’à 330 jours) pour différentes conditions de conservations ont été déterminées. Ces caractéristiques ont été évaluées selon différentes techniques expérimentales de rhéologie, de mesure des variations volumiques, de calorimétrie isotherme, de spectroscopie infrarouge, de porosimétrie par intrusion de mercure, de diffraction des rayons X et thermogravimétrie. / The ettringite binder whose composition is mainly formed by the calcium aluminate cement and calcium sulfate, are widely used in mortars for technical applications such as patching mortars, the self -leveling screeds, repair mortars etc… thanks to their fast hardening ability and high early strength. However, depending on the amount and types of raw materials used in the composition, the properties of these types of binder have different behaviors at early age and at long-term. And in particular in this work, the influence of the nature and dosage of calcium sulfate on the consequences of ettringite mortars hydration as the beginning of setting time, the change from the liquid state to the solid state, dimensional change, the resistance, porosity, the progress of hydration and ageing until 330 days at different conservation conditions were determined. These characteristics were assessed by different experimental techniques such as rheology, chemical shrinkage, autogenous shrinkage, isothermal calorimetry, infrared spectroscopy, mercury intrusion porosimetry, X-ray diffraction, Thermogravimetric analysis.