Phase evolution in electrodeposited Ni-W-B alloy

A ternary nickel based alloy Ni-W-B has been developed for surface corrosion and wear resistance to replace chromium plating, which uses environmentally hazardous solutions. These solutions are not only toxic, but corrosive and carcinogenic. The primary objective of this work was to study the phase evolution upon post-plating heat treatment, which is applied to increase alloy hardness. Phase transformations upon heating were studied by TEM, room and high temperature X-ray diffraction and microhardness measurements. The as-deposited alloy contained 31 wt.% W and had a metastable nanocrystalline-amorphous structure. The maximum hardness of about 900 VHN, which is comparable to the hardness of chromium, occurred at a heat treatment temperature of 400 °C. When heat treated to this temperature, the initial metastable structure decomposed into fine particles of Ni4W in a nickel solid solution. Heating to higher temperatures coarsened grain size and led to decreasing hardness.