Bronze....
I think what your describing is the bronze stator vane section of the pump.
Oh, and they are not really made of plastic. Well, it's plastic but not the kind you'd think of.
That's kinda like saying, I'd ride in an airplane with aluminum wings but not one made with composite materials. If you saw them take these fibers and put them together to form the wings of a plane, you'd probably never fly again!..............(God knows I haven't since finding out)....