Effect of annealing on the structure and hardness of Ni-P-W multilayered alloy coatings produced by pulse plating

Ni-P-W multilayered alloy coatings were deposited on copper foils by pulse plating, using a rotating cylinder electrode. They consisted of layers of h igh (Ni-5 wt.% P-35 wt.% W) and low (Ni-8 wt.% P-15 wt.% W) W content. The wavelengths studied were 8, 40 and 300 nm and the total thickness of the co atings was approximately 25 mu m. The multilayered coatings were annealed i n the temperature range between 200 and 800 degrees C and the effect of ann ealing on their structure was studied by using X-ray diffraction, cross-sec tional transmission electron microscopy equipped:with selected area electro n diffraction facility, and differential thermal analysis. The initially am orphous multilayered coatings crystallise in steps as the annealing tempera ture increases (first the low-W crystallise layers and then the high-W laye rs), and the layered structure is lost around 600 degrees C. The main cryst alline phases formed during annealing are Ni-W solid solution and Ni3P. The wavelength of the coatings seems to affect the onset temperature of the cr ystallisation processes. The hardness of the coatings initially increases r eaching a maximum in the 500-600 degrees C range, and then decreases as the annealing temperature increases. (C) 2000 Elsevier Science S.A. All rights reserved.