The effect of crystallization on the wear resistance of electroless deposited Ni–P amorphous coatings

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Abstract
The changes in structure as well as the hardness and wear resistance of two electroless deposited Ni–P amorphous coatings (with phosphorus content 5.11 and 11.44 wt. %, respectively) after various heat treatments were studied by transmission electron microscopy, scanning electron microscopy (SEM), differential thermal analysis, and x‐ray diffraction. The results show that the hardness and wear resistance go through maximum values with increasing annealing temperature, but the peak of the wear resistance appears at a higher annealing temperature than that of the hardness for 11.44 wt. % P coating. At a given temperature, similar results were obtained with increasing annealing time. It was revealed by structural analysis that the increase of hardness is due to the formation of the Ni 3P phase within the crystallized coatings during heat treatment. The lowering of hardness after the peak value is due to the decrease in lattice defects and the coarsening of grains as a result of recrystallization of the coatings. Different morphologies of the wear tracks were observed in the SEM for the amorphous and crystallized coatings. It is suggested that the wear of Ni–P coatings is influenced not only by its hardness, but also is closely related to the toughness of the coating and the adhesion between the substrate and the coating.

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