Well I did learn something from reading your stuff thanks. We’ve...

Well I did learn something from reading your stuff thanks.
We’ve been talking somewhat at cross purposes because there are 2 fundamentally different ways of doing grain boundary diffusion (GBD).

What you’ve been talking about is forming solid magnets then “pushing” Dy or other metals into the solid magnet under heat (? and pressure). No surprise at all that this crude method is very limited in the size of magnet it can produce, and the centre of such magnets are less enhanced than the boundaries.
Your core refs here were from the SDM company site
https://www.magnet-sdm.com/2017/08/31/grain-boundary-diffusion-magnet/

Look a little closer and they are in fact producing magnets for EV drives using GBD:
https://www.magnet-sdm.com/sdmnews/grain-boundary-diffusion-gbd-technology-sintered-ndfeb-magnet/That’s certainly not the tiny things you referred to (“they don’t make turbines from 1-cm cubes”).

You cited the Yunsheng, again to support your claimed limitation on GBD magnet size:

https://www.yunshengusa.com/technology/gbd-grain-boundary-diffusion.

If you’d looked closer their site also covers a more sophisticated “dual alloy” GBD (DAGBD) method.
This is what I was talking about:

https://www.yunshengusa.com/technology/dual-alloying-technology
They produced 2 kt of this stuff in 2018, the only commercial production figureI could find. (No other sources I found) provide such data.

Here GBD is applied at the powder stage of magnet manufacture. Similarly my previous link:

https://www.stanfordmagnets.com/application-of-grain-boundary-diffusion-technology-in-ndfeb-magnets.html
They describe the process “They deposit Dy vapor on the surface of the particles during the powdering process, and Dy atoms diffuse along the grain boundaries during the subsequent sintering process”. As I commented before, I know of no effective size limit for these more advanced DAGBD magnets and I see no reason why there should be.

These DAGBD magnets are widely available as I posted previously, eg:
https://is.cj-magnet.com/advantage/grain-boundary-diffusion/which has a product list.

https://www.xs-magnetics.com/en/advantage-152.html.

Note the “methods”they offer Traditional, Trad+GBD (“your” method) and GBD (“DAGBD”).

Many of the numerous examples I posted in 64519312 are similar.

GBD magnets are used in automotive drives, a good discussion here:

https://www.emobility-engineering.com/emotor-magnetics/

It’s not explicit which flavour of GBD is being discussed, but as you pointed out “They don’t make turbines from 1-cm cubes”. Nor auto drives.

Similarly https://www.neodymiummagnetics.com/magidea/ndfeb-magnets-production-process/
explicitly lists wind turbine applications for their low Dy magnets. Again DAGBD I assume; basic GBD wouldn’t work as you pointed out.

So in summary (DA)GBD are common in applications, including auto drives and wind turbines and are standard fare in producers’ product lists. Basic GBD is easy but has limitations not shared by DAGBD which used in higher end applications.