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Materials, Manufacturing, and Mindsets: A Recap of the DMSE@IIT Delhi Talk on refractory alloys and CMC composites





I thank the Department of materials science and engineering @IIT Delhi for organising a highly informative talk on refractory alloys and CMC materials by professor Rahul Mitra. 

Prof Mitra presented 2 metallic systems Mo-Si and Nb-Si. Both material systems possess high temperature oxidation resistance exceeding 1000°C. Glassy SiO2 layer formed on the surface being the primary oxidation inhibitor in both cases. As glass softens beyond 1200c it loses some of its oxidation resistant  properties limiting material used in Ultra high temperature environments. 

These systems work but suffer from low fracture toughness that doesn't meet the standards required for aerospace components. Additionally neither Nb nor Mb are easily available and their processing also requires some complicated setup due to the high melting points of these alloys exceeding 2000c.

Therefore it becomes important to keep searching for new materials. Diborides of Zr and Hf are contenders for ultrahigh temp but again fracture toughness is too low and Zr and Hf or even B for that matter are not exactly abundant. 

SiC based composites offer a good balance of oxidation resistance and FT. Carbon Fiber/Sic composites in particular reach very high values making it suitable for use in aerospace applications. With ZrB2 based coatings the maximum operating temperature increases too. 

Yet as professor Mitra noted there are 2 fundamental problems that keep C/SiC systems from gaining widespread adoption. Carbon and silicon are abundant but making Cf/SiC components using these materials is an extremely slow and cumbersome process. Often taking as long as 600 hours using Chemicals Vapor infiltration for densification. 

So it is extremely important to build high throughput systems capable of reducing the time to production. Polymer infiltration pyrolysis has proven itself to be a faster alternative to CVI. Further speed gains can be made by infiltrating it directly with C/SiC slurry instead of precursor polymer. 

Advancements in nanoprocessing have opened other routes for synthesis like dispersion in aq medium and casting paper like sheets before stacking them up to desired thickness and firing. These techniques make rapid production possible. Especially when high efficiency plasma synthesis is used for making sic via SiH4 and Ch4 feedstocks. 

Yet even if these techniques are implemented another,perhaps more concerning, problems remain. That CMCs are not really used as structural materials. A part of this is because of the high cost of production. But that can be brought down by the development of new techniques. A more pressing concern is that they are simply not as tough as metals and need to be thicker to bear the same load. Here CMC sandwich structures could be of tremendous help. These structures increase the load that a component can bear simply by increasing its thickness with the help of a highly porous and hence lightweight core. 

CMCs made of abundant materials like Si and Carbon are extremely important from a strategic POV because even at the low end they can match or exceed FT of wood. And wood has been and continues to be a structural material that is used in everything from household furniture to ships and airplane fuselages and wings. 

Even at 3-5 days that are typically needed to build a CMC component the processing is far faster than the time it takes to grow wood. By learning to engineer components with thicker CMC sandwiches that are still lighter than metals, the possibility exists to  create new kinds of mechanical systems from engines to compressors that can form the basis of the next generation of light weight moderate load bearing,sustainable materials that can be applied to transportation, buildings and power systems. 

In particular components like turbine blades can't really function with thick sandwich composites for blades. But it's possible to design new kinds of compressors that can achieve the same function as turbines do in traditional power plants. Materials science is inherently interdisciplinary and it's essential to engage with the mechanical and electrical engineering community to drive a transformation. Because the payoff is just too big to ignore. CMCs especially Si and Carbon based represent potential material wealth that far exceeds all of the metals combined. We must make this work to our advantage.  

I thank DMSE@IIT Delhi once more for continuing to organise these amazing talks and giving me a chance to engage with researchers who work on cutting edge technologies. Engagements like these can strengthen industry academia relations and encourage exchange of ideas that can lead to new opportunities in the future. I look forward with great interest to attend more such meetings. 

Do you care about international relations? Would you like to be a part of a non profit that seeks to foster international collaboration? Partner with us & use your skills in Science/Engineering/Research/Team Building/Consulting/Administration/Law/PR/Comms/Business to shape the future. Let's do this.

ABOUT bhū 

bhū is a self funded non profit organisation dedicated to advancement of science and promotion of international relations.
We aim to promote international harmony through creation of specific councils and bodies for regulating and overseeing international issues and accelerate developments in nanotechnology, material science ,electrostatics, fluids, plasma science,thermodynamics and advanced manufacturing.

Let us work together


Akshat Jiwan Sharma

Materials science/International relations/Partnerships 

Mobile/whatsapp:+919654119771 

email:getellobed@gmail.com
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