I’ll have to look into it.
at this point, it is looking like hot black oxide, which does meet gov mil spec. But the PVD low temp coating is interesting thanks for posting.
here is the bigger issue with hot application coatings. Any temp that exceeds the 400F temper for the hardened notches, it will reduce the hardness of the heat treat I did.
not only am I limited in temperature I am limited in surface growth also. I’d love to do cerekote but I’m not willing to risk any tolerance problems.
so after lots of exploring, i believe i’ve settled on the hot black oxide bath for now. Which is one of the only options that will keep the application temp where I need it (bath is max 290F), and also not add any surface growth.