Additive Manufacturing (AM) is an emerging part production technology that offers many advantages such as high degree of customization, material savings and design of 3D highly complex structures. However, AM is a complex multiphysics process. Therefore, only a limited number of materials can already be commercially used to produce parts and a handful of others are being studied or developed for such process. Consequently, limited knowledge on this process is available, especially concerning materials that present thermomechanical challenges such as brittle materials.
The research I did during my PhD studies focuses on additive fabrication of silicon pillars on a monocrystalline silicon wafer by Direct Laser Melting (DLM) with a pulsed 1064 nm laser beam. The simple geometry of pillars allowed for the first determining steps into process understanding. Several results were achieved through this PhD work. First, crack-free silicon pillars were successfully built onto monocrystalline silicon wafers. With the help of in-situ process monitoring and sample characterization, wafer substrate temperature and laser repetition rate were found to be the main influential parameters to obtain crack-free samples, as minimum substrate temperature of 730°C and a minimum repetition rate of 100 Hz were necessary to reach this goal (for a feed rate of 15 g/min and a pulse duration of 1 ms). The influence of secondary process parameters such as feed rate and energy per pulse were also discussed. A simple Finite Element Modeling (FEM) model validated by the experiments was used to explain crack propagation in the samples. Then, process monitoring of the DLM process was realized. High-speed camera image analysis re-vealed that vertical stage speed and powder feed rate should match to obtain a constant pillar building rate. As all pillars presented necking at their base, estimations of the thermal characteristics of the pillar during growth were carried out by FEM simulations. They were additionally used to explain the pillar final shape. Finally, the microstructure of the pillars built was characterized by the Electron Back-Scattering Dif-fraction (EBSD) technique. In the conditions presented in this work, the microstructure of the pillar was found to be in the columnar growth mode. The feed rate was identified as the most influential parameter on the microstructure, followed by the stage speed, the impurity content of the powder and the crystallographic orientation of the substrate. Epitaxial growth was achieved on more than 1 mm with a feed rate of 1.0 g/min, a stage speed of 0.1 mm/s, a powder with purity of 4N and a <111> oriented wafer substrate. This work could be further continued by making improvements to the DLM setup, studying the influence of additional process parameters on the thermomechanical behavior and the microstructure control of the pillars, and/or using these results to realize more complicated shapes, either with this setup or by using a powder bed technique.
About
I was born in France and I have grown up in a little town called Beynes, in the department Yvelines, no so far from Paris and Versailles. I am the first of four kids! As a child, I wanted to be a journalist. I have always been interested in digging up into a subject in order to transforming into articles that could be read by others. I had a few friends writing a bunch of articles alongside so we could turn everything into magazines. I spent a lot of time playing with a - now old - layout software in order to make this publication look like my favorite magazines at that time – L’Hebdo, le monde des ados. I even managed to get an internship for a week there!
About
I was born in France and I have grown up in a little town called Beynes, in the department Yvelines, no so far from Paris and Versailles. I am the first of four kids! As a child, I wanted to be a journalist. I have always been interested in digging up into a subject in order to transforming into articles that could be read by others. I had a few friends writing a bunch of articles alongside so we could turn everything into magazines. I spent a lot of time playing with a - now old - layout software in order to make this publication look like my favorite magazines at that time – L’Hebdo, le monde des ados. I even managed to get an internship for a week there!
Discordances
La complexité d’un site classé à l’UNESCO peut se révéler à travers les discordances visibles dans ses détails visuels, son histoire ou ses styles artistiques. Ces discordances résultent souvent de strates d’influences culturelles, d’intérêts personnels, de besoins particuliers ou de périodes historiques diverses. Mais comment ces discordances peuvent-elles générer un lien personnel avec un lieu, tout en permettant de saisir sa résonance universelle ?
Ce souvenir s'inspire du Convento de Cristo, à Tomar.
Les éléments visuels repérés sur le site sont reliés dans une composition linéaire, soulignant leur appartenance à un même lieu. Leurs différences culturelles et temporelles sont mises en valeur par de courtes légendes, renvoyant à une carte dessinée au verso du poster. Le design s’estompe progressivement afin d’inviter le visiteur à prolonger la recherche, à observer d’autres détails présents sur le site — et peut-être même à dessiner les siens.
Ainsi, il comprend que ce lieu ne relève pas seulement du patrimoine portugais, mais peut aussi faire écho à son propre vécu.
Le processus de création a commencé sur le terrain, à travers des visites, des prises de notes et de nombreuses photos de tout ce qui a attiré mon attention. Voici quelques images issues du Convento de Cristo à Tomar, qui ont nourri l’élaboration de mon artefact :
Puis, après avoir analysé ce qui avait attiré mon attention, j'ai réalisé, avec l'aide de nos mentors, que j'étais attiré par les incohérences (dans le temps, le style, etc.) et les détails présents dans les monuments. J'ai décidé de travailler dans cette direction pour créer mon souvenir. Le résultat est une affiche qui entremêle les incohérences trouvées dans le Convento de Cristo, peinte dans ce bleu typique que l'on retrouve dans de nombreuses céramiques au Portugal (ici peint à l'aquarelle et à l'encre) que le public est invité à compléter.
Ce travail a été réalisé dans le cadre de mes études de master à l'Université des Arts de Zurich. Nous sommes partis au Portugal pendant 10 jours afin de participer à un atelier visant à concevoir des souvenirs représentant divers sites classés au patrimoine mondial de l'UNESCO, tels que le couvent du Christ à Tomar, le monastère de Batalha, Coimbra et le monastère d'Alcobaça.