Effect of Heat Treatment on the Characteristics of Electroless Ni-B, Ni-B-W and Ni-B-Mo Coatings

Abstract

In the present work, electroless Ni-B, Ni-B-W and Ni-B-Mo coatings are deposited on AISI 1040 medium carbon steel specimens. Deposit characterization is done using scanning electron microscope, energy dispersive X-ray analysis and X-ray diffraction techniques. The as-deposited coatings present a dense nodular surface morphology in case of Ni-B and Ni-B-W coatings whereas Ni-B-Mo coatings reveal a cauliflower like morphology with aggregated clusters of nickel nodules and visible surface cracks. Heat treatment results in grain growth and visible grain boundaries in case of all the three electroless deposits. Energy dispersive X-ray analysis reveals that the Ni-B deposits are boron rich. The boron content decreases with the co-deposition of W in the EN matrix. From X-ray diffraction analysis it is concluded that the coatings are primarily amorphous in their as-deposited condition and turns crystalline on heat treatment. The microhardness of Ni-B-W coatings is the highest amongst the three in as-deposited condition and up to a heat treatment temperature of 400°C. While Ni-B-Mo coatings show higher thermal stability.