Single-crystal? Please elaborate.
“Single-crystal” means the blade is cast rather than machined/forged, and cooled rapidly enough that the molten metal doesn’t have time to form a crystalline structure - the whole thing is one big metal crystal.
A normal cast or forged piece of metal is composed of numerous (nearly) microscopic crystals of the metal alloy. They're often called "grains", and the boundaries between the grains can tend to weaken the structure or be focal points for defects.
It is possible (and the technology isn't new) to form metal parts in complex shapes which are composed of a single crystalline structure. They have no grains and no grain boundaries. Consequently, they are structurally much stronger, and can therefore be much lighter, than conventional polycrystalline parts.
A common application of this technology is jet engine turbine blades.
I am not a metallurgist.