Abstract
This paper investigates the effect of crystallization on wear and corrosion behavior of the electroless Ni-P/Ni-B duplex coatings on ferrous PM compacts. The PM compacts were plated with Ni-P and Ni-B by the electroless deposition method. The duplex coated samples were heat-treated at 300 and 420 °C for 1 h, according to the major crystallization temperatures of the coatings. Samples were examined and characterized by DSC, XRD, and SEM. Wear tests were performed by using a pin-on-disc tribometer under 30 N normal load. Electrochemical corrosion tests were also carried out. XRD patterns reveal that the structure of the as-plated Ni-P/Ni-B coating is amorphous. Heat treatments caused an increment in the hardness and wear resistance of coatings due to precipitation hardening by the formation of the hard phase. It was also found that the as-plated coating shows better corrosion performance in comparison with the crystallized coatings.

Key words
electroless, crystallization, heat treatment, hardness, wear, friction

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