​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!
Mismatches
How can mismatches trigger personal connections to a site with awareness of universal relevance?
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The complexity of a UNESCO site can be admired through mismatches in its visual details, history and artistic styles. These mismatches result from overlays of cultural influences, personal interests and needs, or periods of time. How can those mismatches trigger personal connections to a site with awareness of universal relevance? This poster focuses on the Convento de Cristo in Tomar. The visual details picked on the site are linked in a linear composition to underline their belonging to the same site. Their cultural/temporal differences are highlighted by small captions referring to a map drawn on the back of the poster. The design fades away to invite the visitor to continue searching for other details that he discovers in the site, and maybe draw his own. This way, the latter is invited to understand that the site is not only relevant for Portuguese heritage but also for his own.
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The design process started on the field research, visiting the sites and taking pictures and notes about everything that caught my attention. Here are a few pictures that inspired my artefact, from Convento de Cristo in Tomar:
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Then, after analyzing what caught my attention, I realized, with the help of our mentors, that I was attracted by the mismatches (in time, style, etc.) and details present in the monuments. I decided to work in this direction to create my souvenir. The result is a poster interweaving the mismatches found in Convento de Cristo, painted in this typical blue found in many ceramics in Portugal (here painted with watercolors and ink) that the public is invited to continue.
​This work has been realized in the frame of my Master's studies at the Zürich University of the Arts. We went to Portugal for 10 days in order to attend a workshop to design souvenirs representing diverse UNESCO sites such as Convent of Christ in Tomar, Monastery of Batalha, Coimbra and Alcobaça Monastery.