Okabe Rintarou
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The CMC you are talking about have a Silicon Carbide matrix, but are reinforced with Carbon fiber, not Silicon Carbide fiber. Such older CMC tech is already in use in GE-414-400 engines (the non EPE GE-414) as well as F100 engines for F-16. Its primarily used in the nozzle flaps.
The kind we need is Silicon Carbide matrix reinforced by Silicon Carbide fiber.
Work is required to first produce SiC fibers of desired quality, followed by proper fabrication of SiC-SiC composite. I did some digging and found this recent (2016) patent by DRDO for a melt spinning-curing-pyrolisis process for making SiC fibers. A cursory glance at the numbers tells me that we have barely achieved 1st generation SiC fibers.
DRDO patent: https://www.quickcompany.in/patents/a-process-for-the-preparation-of-silicon-carbide-ceramic-fibers
GE is beyond 4th generation SiC fibers right now. And their 3rd generation SiC fiber based CMC are used in non-rotating parts of CFM-56 LEAP engines. The first generation we have achieved does not even have completely crystalline microstructure. Subsequent work should focus on removal of Si-O phases and then reduction in amount of carbon phase precipitating at grain boundaries as well as increase in size of grains. Aim is to achieve a near-stoichiometric crystal microstructure with large grains. This will give us 3rd generation SiC fibers. For further improvements to creep resistance, subsequent generations have focused on even larger grain sizes and a microstructure almost free from pores and impurities. Boron Nitride coatings are also applied on the fibers to prevent unrestricted crack propagation from the matrix into the fiber. In India, none of this is done yet. All we have managed till now is an SiC fiber with a microstructure that has a largely amorphous structure, which is against the basic principle of why any kind of fiber is used in any kind of reinforcement.
Exactly. Once the SiC fiber process gets matured. Its not mature yet, for reasons I mentioned above. First they need to mature that process, then they'll reach the starting line for SiC-SiC composites, i.e. employing SiC-SiC components in nozzles and then slowly improve it to apply in stators (vanes). GE already uses these things in commercial engines. Has been doing so for a while. We will also need to work on the environmental barrier coatings. Although the experience of DRDO with C/SiC CMC will help, GE also went through C/SiC stage before reaching to where it is now. DRDO has a long path ahead and the least government can do is aid them by creating a National Mission on Gas Turbine Technologies. We need clear goals, not the current ad-hoc approach, if we want to catch up to GE.
Not that simple. I highlighted the challenges to achieving CMC for non-rotating parts. In addition to those challenges, CMC in turbine blade adds the additional challenges of sustaining high cycle fatigue due to vibrations of blades, low cycle fatigue in the root that dovetails with the disk, centrifugal forces requiring better creep resistance, rubbing of rotating blade tips with turbine shroud, etc. Creep resistance needs to be much better. There is a reason GE is celebrating the achievement of rotating CMC parts.
