INFLUENCE OF SURFACE MORPHOLOGY ON THE MICROHARDNESS OF ELECTROLESS Ni-B DEPOSIT REVEALED BY AFM OBSERVATION

A crystalline and non crystalline two phase Ni B coating was prepared by electroless deposition with potassium borohydride as reducing agent. When the deposit was heated from 10 °C to 500 °C , it took place three kinds of phase transformation and formed corresponding nickel borides. An Atomic Force Microscopy (AFM) was used to directly view the surface morphologies of the samples in various treated states. The AFM images indicate that nano dimensional protrusions grow on the surface of the deposit grain during some heat treatment processes, and they are distinguished greatly from the small bulges existing in the as plated deposit. Further studies show that the microhardness related to the surface topography of the coating to some extent. Especially when a two step heat treatment process was performed, the nano dimensional protrusions on the grain surface grew upt to 40～100 nm in diameter and 10～20 nm in height, and the deposit microhardness reached up to HV1500～1600 in the meantime.