Ni-B alloy deposits were successfully formed over alkali surface treated boron carbide by electroless technique and the effects of processing parameters such as reduction bath pH, temperature and post-heat treatment were investigated. Microstructural studies show remarkable changes in structural morphology from mesh-like structure to platelet type Ni-B coating. The main Ni-B phases observed were NiB, Ni 2 B, Ni 3 B and Ni 4 B 3 . An effective Ni-B alloy coating with better surface characteristics was formed at pH 8 under 75uC reaction bath temperature in the presence of bath stabiliser. The post-heat treatment of Ni-B coated particles under varying bath reaction temperatures at 400uC showed remarkable Ni-B phase transformation from metastable NiB and Ni 2 B to stable crystalline Ni 3 B phase. The NiB coated particle shows lower particle-matrix interfacial reaction, better wettability and enhanced dispersion in aluminium composites compared to uncoated particles.
Electroless nickel coating is one of the versatile methods to improve the physical properties of aluminium alloys. The increasing demand for high corrosion resistant surface with improved performance leads to the development of poly-alloy and composite coatings with the aid of ultrasonication. In the present study Ni-B alloy and Ni-B-CeO2 composite coatings were made on 356 aluminium alloy surfaces. The variation in structural and mechanical properties of coatings formed under both ultrasonication and magnetic stirring were investigated. Surface analysis by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) has shown the formation of more uniform coating under ultrasonication. The electrochemical polarization tests show enhanced corrosion resistance in ultrasonic assisted coatings.
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