LAUSR

Abstract Ni-B coatings were electrodeposited in a modified Watts bath containing trimethylamine borane (TMAB). Chemical composition, phase constituent, texture and morphological characteristics of the as-deposited and isothermally annealed (300 °C) coatings were investigated as a function of the boron content (CB) using inductively coupled plasma spectroscopy (ICP), X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The nanostructural features of selected coatings were investigated using high resolution transmission electron microscopy (HRTEM). The results indicated that the CB of the deposits increases with increasing the TMAB concentration (CTMAB) in the deposition bath, and the maximum boron content of 4.2 wt% is obtained at CTMAB = 7 g/L. By increasing the boron content of the as-deposited coatings; (i) XRD peaks widen and lose their intensities, (ii) preferred orientation changes from (200) to (111), (iii) grain size of crystalline phase reduces from 13 nm for pure Ni to 2.3 nm for Ni-4.2 wt% B coating, and (iv) spherical surface morphology becomes finer. The HRTEM analysis of the Ni-2.5 wt% B coating revealed the formation of a two-phase structure consisting of equiaxed nanocrystalline domains (nanograins) with average size of 4.3 nm embedded in a thin layer of amorphous phase. Isothermal annealing at 300 °C for 1 h enhances crystallinity of all the studied coatings and increases grain size and changes preferred orientation of the pure Ni coatings from (200) to (111) while grain size and preferred orientation of alloy coating remains nearly unchanged.