A quick announcement to tell you all that Materialia Indica now has a second home which is bigger, more open, and more feature-rich.
Any crystalline material contains many defects. Depending on the topology of the defects, they can be classified as point, line, surface and volume defects. Of these, only point defects are equilibrium defects — that is, at any temperature above absolute zero, it is energetically favourable for the system to create these defects — a specific number of them, which number, varies from system to system and within a system with temperature. An example of a line defect is the dislocations; an example of a surface defect is the grain boundary.
In some circumstances, the surface defect, namely, the grain boundary, can be considered to be made up of line defects, namely, the dislocations. Though such dislocation models of grain boundaries date back to early 1940s, Read and Shockley, in a classic paper in 1950 , used such a model to calculate the energy of a grain boundary — which continues to be a landmark study. In this post, I will discuss this paper of Read and Shockley.
The conventional analytical treatment of actual systems can in fact only be successfully performed in the simplest cases. It fails when a more or less realistic model of multiphase alloys in considered. As a matter of fact, computer simulation is a new approach to the probelm and is applicable to real alloys. The computer makes it possible to solve problems that have been considered unsolvable. The use of high-speed computers for modeling the processes occurring in alloys cannot be obviated, and I believe that computer-simulated research will form a new field in the material sciences.
Even the first attempts to simulate, with the help of computers, the martensitic transformation and the strain-induced coarsening in decomposed alloys using but idealized crude models gave an encouragingly good description of those processes, and the results obtained are sometimes in excellent agreement with electron microscopic observations. We may hope that the use of more realistic (and therefore more elaborate) models will make it possible to come close to theoretically predicting the structures of two-phasealloys applied in industry.
There is another problem that should be mentioned. The physical processes occurring in alloys are affected by varied factors that sometimes conceal the important characteristics of the phenomenon. Eliminating them may be a difficult problem which can hardly be solved in all cases. From this standpoint computer simulation serves as an “experiment” carried out under ideal conditions in the absence of any interfering factors.
– A G Khachaturyan, Theory of structural transformations in solids, 1983.
I am Suchismita, a new blogger to Materialia Indica. For the last 8 years, I have been with the Materials Research team at GE Global Research. I am also an alumnus of IISc, so when Abi mentioned about Materialia Indica, I was very excited to be part of this opportunity to touch base with my alma-mater, and the extended materials community at large. I will start with sharing the story of our materials team at GE, and what we do.
Materials Research Lab at GE Global Research, Bangalore, consists of about 35 scientists. In the true spirit of this unique engineering discipline, we have experts from all fields- metallurgists, chemists, physicists, materials scientists, mechanical engineers, all coming together to develop better materials for a variety of applications: ranging from superalloys & coatings for jet engines, to materials for sustainable energy sources, materials for lighting applications, scintillators for healthcare applications, and so on. We have a Metallurgy lab and a Ceramics lab, and I will talk about the Metallurgy lab to begin with.
The Metallurgy lab has aligned itself into 3 CoEs (Centers of Excellence) – Corrosion, Structure Properties and Modeling & Tribology. While each of these are individually anchored in metallurgy, they represent distinct technical skill sets by themselves.
Corrosion CoE is rooted in physical metallurgy and electrochemistry. Over the years the CoE has developed unique competencies to study localized corrosion under high pressure and temperature using autoclaves and potentiostats to arrive at materials or process environments that are not prone to localized corrosion or crevice corrosion. This CoE has now built unique capabilities to evaluate materials for sour gas environments.
Modeling CoE has its foundations based on multiscale modeling. Atomistics & first principles calculations provide critical inputs on thermodynamic parameters such as stacking fault energies, APB energies, etc. that feed into next scale Phase Field models. Ab initio modeling is also invaluable as a stand-alone tool when it comes to understanding surface reactions: extremely useful for designing next-generation coatings. Thermodynamic modeling follows next, to complement this information & feeding into microstructural models based on Phase Field or Cellular Automata, which track the microstructural evolution during solidification and as-solidified structures. The end aim of all of these is however, to tie up with higher scale mechanical behavior models, to fit the last piece of “structure-property” modeling. CDM(Continuum Damage Mechanics) based models or other strength models then provide with component strength information based on inputs from all the above length/time scales.
Tribology CoE has been at the forefront of developing relationships between thermal sprayed and PVD coating structures and wear properties – specializing in developing customized test methods to simulate different forms of wear, and through the understanding of the wear mechanisms derived places bets on new and existing coating structures to solve customer issues. These are evaluated through customized test set ups to demonstrate improved performance under close to field conditions.
Here’s just a flavor of the different teams we have in Metallurgy and our focus areas.
Sounds too serious? Well, I must admit, that our time at work is not consumed by only the above. To entertain our fatigued brains, we have regular screenings of Bollywood blockbusters & musical extravaganza at our amphitheatres, in addition to the gym facilities & entertainment center equipped with pool tables, TT, & other indoor games. National religions such as cricket & football tournaments are frequently celebrated! And I must say, that a lot of ideas buzz out of these informal meets under fun-fare alongside scheduled brainstorming meetings. Overall, the culture of open exchange of fundas between people of diverse disciplines make this place a great learning centre!
I will be back to share specific materials stories with you soon, but, here’s some food for thought before I leave-
Did you know: The widely known beneficial effect of Boron in enhancing ductility in Ni-base alloys was actually a serendipitous discovery through contamination from crucibles containing B during melting of the alloy. Here’s a snapshot of the original 1958 article:
Recent issue of Materials Today reports:
In the realm of science fiction, the idea of tiny nanorobots that can enter the human body and seek out and destroy unwanted elements has been prevalent. This idea has been made a reality by a research team led by Bin Kang and Yaodong Dai at Nanjing University and the Georgia Institute of Technology. They have used what is called the photoacoustic effect of carbon nanotubes (CNTs) to make what are essentially nanogrenades that can target and destroy cancer cells.
[Original work: Kang et al., Small (2009), doi: 10.1002/smll.200801820]
A soap bubble is an extraordinarily beautiful thing and yet it requires virtually no skill to produce. This is because surface tension does all the work for you, making sure that a perfect spherical membrane is produced every time. In fact it is impossible to blow imperfect bubbles. Even if you try to blow the bubble through a noncircular orifice you may at first achieve a temporary nonequilibrium shape [...] but the end result is always a perfect sphere.
In this chapter we will show how such beautiful but tyrannical surface tension effects can be investigated using the computational equivalent of soap bubble solution: the Potts model. Like soap bubble solution is is easy to use and provides fundamental insights into surface tension phenomena; but also like soap bubble solution, it can lead to a sticky mess.
– Mark Miodownik, Chapter 3. Monte Carlo Potts Model, in Computational Materials Engineering: An introduction to microstructure evolution, Edited by K G F Janssens, D Raabe, E Kozeschnik, M A Miodownik, and B Nestler, Academic Press, 2007.
Potts model is widely used in the materials science literature to simulate a wide variety of microstructural features and phenomena: be it grain growth — normal and abnormal, recrystallization or Zener pinning (and, the article by Miodownik, from which I quote above, discusses all these and much more). In fact, to quote Miodownik again,
At the moment for large 3D systems, with complicated textures and pinning phases, the model has no equal.
In this Classics in Materials Science post, I would like to talk about Potts model and the paper in which Potts outlined it .
Overcoming the difficulties of nanotechnology water treatments means developing innovative solutions to engineer a usable product. One answer could be to develop methods where the nanoparticles need not be suspended in the water. For example, one can stick — or ‘immobilise’ — the nanoparticles onto suitable materials such as steel or polymer sheets,which in turn can be easily dipped in and out ofwater tanks to work as catalysts or adsorbents.
This needs care to retain nanoparticles’ size and integrity so as to keep the benefits of operating at the nanoscale. But if it can be done, immobilisation is a good technique since it would keep water free of nanoparticles during and after water treatment. We, here at the Indian Institute of Science, Bangalore, are developing such a technique for degrading organic molecules using nano titanium dioxide. The results have been very promising and we are working closely with the University of Johannesburg to scale up the process in the near future.