Well, have sent an email reply to him, pointing out some of the "perception issues" that gets propagated in most of these webcasts - here's the operative part of it.bala wrote: ↑14 Jun 2026 21:25 India Cracks the Jet Engine Code? DRDO’s Single-Crystal Blade Breakthrough Explained I Aadi
MIDHANI alloy and technique to grow single crystal turbine blade is being discussed. Also some amount of cooling tech is involved by micro drilling laser holes into the blade. This has to be shown as a repeatable process and undergo actual tests in the field, for high temperature repeated stress regime.
https://www.youtube.com/watch?v=FDCvL44Iwd8
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// looks like there is some progress made since many YTs are claiming such things. Hope it is all true and actual Kaveri emerges as field deployable engine on Tejas.
I'm sure such emails will get ignored, as always - however thought, some here may find some of these points helpful (wrt understanding the perspectives of what is being talked here - pls refer heavily to my old posts for more context and details):
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An email like this is more or less futile to cover a vast topic like this, but I’ll limit to max 10 points, strictly – and may I make a humble suggestion, to refer back my posts/writings on these topics, for better part of 2 decades now, in the Bharat-Rakshak forum, for better appreciation of this topic.
1) Single Crytal is one of the various Casting Technologies, the 3 most prominent ones being Polycrystalline/Equiaxed, Directionally Stabilised (DS) and Monocrystalline (popularly called as SC).
a) In Equiaxed/Polycrystalline casted blade innumerable microscope “fault lines” (called grain boundaries) runs across/transverse (so perpendicular to tip-to-bottom axis of the blade). So, at a relatively low temp (say around 750deg C), given the extreme pressure blades (due to high centrifugal forces from a ultra-high-rpm) any inevitable cracks rapidly propagate across these fault-lines and destroys the turbine blade.
b) In DS casting, attempt is made to remove these grain boundaries by controlling two major (amongst innumerable) casting factors:
i. the temp gradient at the boundary (of molten metal and solidifying metal)
ii. extremely slow cooling/solidifying of molten metal
However, what really happens is that a few grain boundaries still form, but they now run parallel to the blade axis (from top to bottom) – for Polycrystalline it’s tranverse to blade axis.
So crack-propagation becomes slow until it reaches the “first” of these grain boundaries but then again slows down until it reaches the next, roughly parallel, grain boundary.
c) SC casting is just a slightly more advanced version of the DS casting tech – where-in the aim is to remove all grain boundaries. The only diff is introduction of a “pig-tail looking” grain-selector at the base, which allows only one crystal to survive, and then “fill up” the entire blade. So, theoretically atleast, no grain-boundary, no crack propagation etc.
Technical reality ofcourse is something else.
2) Single Crystal (SC) Tech is not new, dates back to early 80s, P&W pioneered it (while DS is from 60-70s). However, there are various gens of SC turbine blades, and worse some of the later gens of DS blades are found to be more effective than 1st Gen SCs.
3) Without going into too many technicalities, do note that the effectiveness of SC casted turbine blades, also depends quite heavily upon how the Ni-Superalloy (the base material) is “designed”.
Normally, it’s not uncommon to have 20+ rare-earth (and not so rare) metals, “mixed/dissolved”, in a furnace (VIM furnaces), to come up with SC-castable Ni-Superalloy. The weight-precision of these is upto 2 decimal points %.
You may want to look up Rhenium, Molybdenum, Tantalum, Tungsten, Ruthenium etc % used in, say, just as an example, in a second gen SC like CMSX4.
Each of these metals have an important role to play and even a slight mismatch in the proportion more-or-less makes it useless. Anyway, a raw SC (or for that matter DS) casted blade is completely useless without the post-cast ageing and high-temp hardening cycles – without which these blades won’t last even a few hours and which is why the OEMs simply love to keep these parameters secret.
Something like: “How don’t you take this Superalloy billet, mfg the SC casted turbine blades from them based on the parameters we have told you and return back them to us – we will do the post-cast Ageing and Hardening for you and ship them back?”
4) The myth is that without SC blades in turbines, high turbine inlet/entry temp (TeT) is impossible. Here are some examples (from memory, you can validate via simple Google search):
the raw-metal temp of AM1 (1st Gen SC, used in M88-2 of Rafale) is 1045-60deg C while the TeT is 1560-80deg C; the SC based Turbine-blades of Al-31FP (mfg, including casting of LPT blades, by HAL (at Koraput) allows TeT of ~1380-90deg C.
A 2nd Gen SC like CMSX4 has raw-metal temp capability of around 1070-80deg C.
the raw-metal temp of CM247LC (3rd Gen DS, used in Kaveri of LCA) is 1050deg C while the TeT is 1455deg C; similarly, the DS blades used in RD-33 series, allows TeT of ~1200-50deg C.
Oh betw, HAL has been manufacturing DS based blades from early 2000s (for Adour of Jaguars).
F414 uses 3rd Gen SC blades of the Rene series – so does EJ200.
5) These above examples will tell you very little (comparatively, though from Material SC pov, they are generational gaps) diff between later gen DS and various gens of SC blades. The gap between raw metal temp and TeT of the blades themselves (eg refer to M88-2 of Rafale, 1060deg C vs TeT of 1580deg C) is because of few other technologies e.g blade cooling architecture (both internal and external Film cooling), Thermal Barrier Coatings (TBCs) etc.
Long back I’d written a 6-part series on TBC – the last-part has a graph which explains this aspect, you may want to go thru it (viewtopic.php?p=2638605#p2638605).
6) Of course, when compared to DS .casted technological capability, there are quite a few technical challenges like Alumina vs Silica (used for DS blades) cores, higher pouring temp capability, the “black art” of controlling higher level of S&W (Shrinkage and Wrapping) in the mold, even higher thermal gradient maintenance, an order of slow-removal rate etc etc etc – but none of these are insurmountable for any decent technologically capable nation who has mass-manufactured DS casted turbine blades, and that too for decades.
7) However, typically the rejection-rate of SC casted turbine blades are very high (sometimes as high as 70% etc) – due to various factors like LAB (Low Angle Boundary) and HAB etc (again pls refer to my writings in BR forum). That’s one of the major challenges wrt mass-manufacturing of SC casted turbine-blades etc – so much so, even the mighty GE, once upon a time, reverted back to 3rd Gen SC (of the Rene series) for the F414 series, even after fully-realizing turbine blades from 4th Gen SC.
Having said that adding so many refractory metals, increases the density (and thus the weight) of the blades – so SC blades are no silver-bullet either. Specifically, wrt the NGVs as they are the ones who bears the full impact of “high TeT” – but being larger (than blades), they are notoriously tough to cast, more so wrt SC casting.
Betw, why strictly SC casting – what about 3D mfg tech like LBF (SLS/SLM tech) (hint: HTSE by HAL – but then again, Sarkari HAL, so must be useless, never mind).
DMRL/GTRE/MDNL et all have demonstrated SC casted Turbine blades for 1.5+ decades now (eg since nobody visits their unglamorous stalls, but those who do, would have known/seen them in GTRE stall of AeroIndia 2013). Similarly, decades back DMRL have demonstrated a 4th Gen SC castable Ni-Superalloy called DMS4 (preceded by DMS3, a 3rd Gen SC Ni-Superalloy).
For ref, the 4th Gen SC casted blades provide ~1120deg C raw-metal temp capability, which helps pushing the TeT beyond forbidden 1600deg C TeT territory (say in the F135) – of course, it’s much more nuanced, as it’s not a simple linear addition (hint: TBC material limitations etc).
9) But since, in our country, all Sarkari work is considered useless and worthless, there was no funding to take these achievements to mass-manufacturing level for 2+ decades now. Same is the case with SC casted turbine blades. And with 0-funding for Kaveri program (thus conveniently keeping the import option open for many decades in future), there were no justifiable use cases either.
Having said that, CMSX4 based 2nd Gen SC blades were mfg by HAL and used in Shakti engine (for ALH) for a decade+ now. Ditto wrt the SC casted turbine blades for AL-31FP.
In both the cases the raw-Superalloy is imported (in billet form) though, however the SC casting itself is done indigenously (obviously the material OEMs, provided the casting parameters and tolerance values etc), which means wrt SC Casting technology we have been (and are still) atmanirbhar, for 1.5+ decades now.
10) Kaveri achieved the all-important dry-thrust of 51KN back in 2007-08 – and thus needed to be abandoned (post haste in ~2009-10), as it would have blocked all future foreign imports. And it failing to achieve 81KNWet Thrust (71-72KN) gave that perfect excuse to do so – most, more so the media-types, are anyway clueless wrt diff between dry and wet thrust, and technologically, which one really defines Turbofan technology maturity/capability.
To expect them to even question exactly how much of the shiny-brochure-advertised-thrust-figures these foreign TFs actually achieves in our vast plains betw, say May-Aug or say in Leh. Will the same happen (or would have happened) with Kaveri?
… etc etc etc
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