A metal matrix composite material made of a fiber reinforcement having a coating of gadolinium and gadolinium boride, preferably as discrete layers, each having a thickness of 1 to 6 microns. This composite is made by coating reinforcing fibers with gadolinium using a deposition technique, further coating the fibers with gadolinium boride by a deposition technique and then consolidating the coated fibers into a metal matrix to form the metal matrix composite.