Influence of Annealing Temperature on the Phase Transformations of Composite Electroless Ni-P-X, X=SiC, Al(2)O(3) Coatings

Abstract

This paper presents a characterization of the phase transformations observed in a series of electroless Ni-P coatings on aluminum containing 2 wt. % of SiC or Al(2)O(3) particles and heat treated at 300 or 400°C for an hour. The composite electroless nickel coatings obtained were characterized using optical microscopy, scanning electron microscopy, microanalysis, interferometric microscopy, microhardness tests, roughness evaluation, and X-ray diffraction. The results indicate that the presence of the particles leads to a slight increase in the microhardness and the roughness of the deposits. Additionally, the coatings undergo crystallization and generate nickel phosphide (Ni3P) upon heat treatment at 400°C for 1 hour. A precipitation hardening mechanism significantly increases the microhardness of the coatings.