I defended my PhD thesis one year ago (April 7th, 2022) at Cemef, ENSMP (Mines Paris) in France. This week I had to search one of my phd advisor articles on google scholar and I found that my thesis was posted online in HAL Archives Ouvertes on March 15th (2023), check it here. I am proud of writing my thesis, it was challenging, I am not the best writer even in my mother tongue, I am not a native english speaker, but I did it!

The title of my thesis is Towards a precise description of the grain boundary mobility and energy for their numerical integration in finite element modeling of recrystallization and grain growth mechanisms. This is the abstract in case you just want to read that and don’t want to download the whole thing 1: The relation among process, microstructure, properties, and performance of materials is of great interest to the metal forming industries. The microstructure-properties relationship has opened an exciting branch of materials science called Grain Boundary Engineering: control the grain boundary character distribution to promote specific materials properties. The manufacturing process of metals can be modeled at the mesoscopic scale using numerical tools that describe the evolution of grain boundaries. The Level-Set (LS) approach in the context of Finite Element (FE) formulations remains a powerful tool that allows mimicking industrial thermomechanical treatments where large deformation can take place.This work aims to improve the FE-LS framework by including enriched grain boundary energy and mobility models and applies the enriched framework to the simulation of grain growth and recrystallization in a single phase austenitic steel. Accounting for the heterogeneity or the anisotropy of GB properties is necessary if special boundaries or subgrains have to be considered. The improvement of the GB property models was incorporated in different FE-LS formulations using additional terms in the existing kinetic framework. Noteworthily, the current knowledge of GB property data and models still suffers from the lack of relevant and accurate experimental data. The complete description of GB properties calls for high spatial three-dimensional microstructure analysis, and for temporal evolution under given thermomechanical conditions, which remains unattainable with the state-of-the-art techniques.Based on partial experimental data acquired in this work, existing molecular dynamics data, triple junction test cases and polycrystalline simulations, it was confirmed that the Anisotropic formulation was the most physical formulation. Nevertheless, when low levels of heterogeneity/anisotropy are involved in the considered microstructure, the isotropic formulation can be used safely in grain growth and recrystallization simulations. Finally, the new proposed numerical framework is shown to be able to model coherent and incoherent twin boundaries individually or immersed in a polycrystalline microstructure.

If you are interested or you are a first year PhD working on Grain Boundaries or a Metallurgy realted ubsject, I recommend the first chapter!! :) Cemef is a wonderful place to do research, I met wonderful people and my PhD advisor’s were great. I miss them… If you want to work on metal forming and related topics don’t hesitate to contact them!

Let’s go to the present. This year a lot of changes happened, I got married with the most amazing person in the world and I moved to the USA 2. I am a postdoc at Johns Hopkins University, I love Baltimore and its people! However, the USA has a lot of wierd policies for visiiting scholars, for instance, my wife has to wait between 3 weeks and 3 months to receive a work authorization (fingers crossed) but in the mean time we have to make a live with one salary. If you didn’t do grad school you may say, “oh, it’s ok, a PhD has to earn enough money as a potdoc”. Meehhhh… noooooo! Academia is so cheape. Raise salaries or let our family members work and enjoy more of our visit. I am even thinking about go back to France, or moving to the industry, I just received an offer to work in High Performance Computing with better conditions. I just loved materials science and computational mechanics that I know I’ll miss it a lot.

Let’s see what happens… everything is going to be ok and I’ll keep learning.

1 I understand, besides my PhD jury, me and my PhD advisors, who else wants to read around 200 pages.

2 Yes, moving from France to the USA is such huge change, but this changes just make me grow.

Author: Brayan David Murgas Portilla. This is a personal note, my furutre self will read it and laugh, I know it.