I assume they mean crystalline domain heterogeneity. The best metals are single-domain so that there are no fissures along the boundaries. But that takes very p

I assume they mean crystalline domain heterogeneity. The best metals are single-domain so that there are no fissures along the boundaries. But that takes very pure material and very slow cooling. A good alternative is nanacrystalline or amorphous domains, which are fairly simple, just blast with microwave energy during cooling. This can make a very strong metal with great working properties, a bit softer, but doesn’t fracture.