Nanocrystalline electroless nickel poly-alloy deposition: incorporation of W and Mo

Autocatalytic quaternary Ni-W-Mo-P films were prepared using alkaline citrate based baths and compared with binary Ni-P and ternary Ni-W-P, Ni-Mo-P coatings. Energy dispersive X-ray analysis showed that the binary Ni-P deposit contained 12.2 wt-% P. Codeposition of tungsten in Ni-P matrix resulted in ternary Ni-W-P with 4.1 wt-% P and 5.2 wt-% W. Incorporation of molybdenum led to a ternary Ni-Mo-P deposit containing 4.1 wt-% Mo and 11.2 wt-% P. Presence of both sodium tungstate and sodium molybdate in the basic bath resulted in a quaternary coating with 3.6 wt-% W, 6.7 wt-% Mo and 2.5 wt-% P. X-ray diffraction patterns of all the deposits revealed a single peak for Ni (1 1 1). The quaternary alloy exhibited a sharper peak showing the more crystalline nature of the deposit. Field emission scanning electron microscopy studies of the deposits showed the presence of smooth nodules for ternary deposits, but coarse and well defined nodules for quaternary deposits. Phase transformation behaviour of the ternary Ni-W-P deposit revealed a single exothermic peak at 440 degrees C. However, ternary Ni-Mo-P deposit exhibited a split type high temperature peak at 397 and 461 degrees C and the quaternary Ni-W-Mo-P deposit showed a single high temperature peak at 485 degrees C. Microhardness measurements showed that the quaternary Ni-W-Mo-P deposit exhibited increased hardness of 920 HV(50 gf) when heat treated for 1 h at 400 degrees C.