Structural analysis of electroplated amorphous-nanocrystalline Ni-W

Ductile nickel-tungsten (Ni-W) alloys containing about 20-21 at.%W were electroplated onto copper substrates. The development of the amorphous/nanocrystalline microstructure towards a complete crystallization by isochronal heat treatments in vacuum was monitored by different methods. For medium annealing temperatures a solid-solution of W in the fcc-Ni lattice was achieved resulting in an increased hardness. For temperatures of 600 degrees C and upward recrystallization started and thermodynamically stable intermetallic compounds like Ni4W and NiW were formed. A third phase, containing more than 80 at.%W was also detected but could not be identified so far. Only by combination of different methods and especially by use of analytical TEM structural analysis and phase identification in these amorphous-nanocrystalline Ni-W alloys were successful.