Phosphorus Particle Composite Plating with Ni-P Alloy Matrix

Ni-P alloy films containing phosphorus particles (called "Ni-P alloy composite films") were fabricated by electrodeposition and were subsequently subjected to heat-treatment. Their compositions and microstructures were characterized, and their friction properties were evaluated using a ball-on-plate method. Composite electroplating in the nickel sulfate and chloride bath containing phosphorus acid and micrometer-sized phosphorus particles resulted in the Ni-P alloy coating with enhanced deposit phosphorus content. The phosphorus content of the films increased with increasing phosphorus particle concentration in the composite plating baths, reaching a maximum value of 29.0 atom %. The phosphorus particles were homogeneously distributed in this Ni-29.0 atom % P alloy composite film. Heat-treatment converted the phases of the alloy composite films from an amorphous phase to stable crystalline phases, which are the same as those in the Ni-P binary alloy phase diagram. The friction coefficients of the Ni-P alloy films increased with increasing cycle number, whereas those of the Ni-P alloy composite films remained relatively constant. The alloy composite films had lower friction coefficients than the Ni-P alloy films both before and after heat-treatment. These results indicate that phosphorus particles are beneficial for maintaining a lower and stable friction coefficient during the ball-on-plate reciprocating friction test.