Production and microstructural characterization of Ni matrix composite electrodeposits containing either micro- or nano-particles of Al

Abstract

Composite coatings electroplating could be a valid and relatively low cost production method to codeposite either micro- or nano-particles of Al in Ni matrix. The aim of this work is the production of Ni matrix composite deposits containing either micro- (3–4μm) or nano- (130nm) particles of Al using parallel plate geometry composite plating and their characterization both prior and after heat treatments at different temperatures by means of microstructure and microhardness. The obtained electrodeposits both before and after heat treatments at different temperatures have been observed by SEM in cross section both prior and after metallographic etching and analysed by XRD in order to evaluate the formation of Ni/Al phases. After heat treatment at 600°C the micro-composite coating consisted of a biphasic γNi and γ′Ni3Al system, while after heat treatment at 800°C of a solid substitutional solution of Al in the γNi. The diffusion of Al in the metal matrix hindered the recrystallization of the Ni matrix and the change of the preferential orientation. The more uniform distribution of the Al nano-particles and the smaller dimensions lead to an advance of the diffusion at lower temperature (400°C). The heat-treated nano-composite deposits consist of γNi and present a columnar structure with narrow ad short columns as the fast diffusion of Al blocked the recrystallization of the Ni matrix.