Crystalline and Amorphous Electroless Co-W-P Coatings

• Published in: Journal of the Electrochemical Society Vol. 152; no. 9; pp. C612 - C619
• Main Authors: Armyanov, S, Valova, E, Franquet, A, Dille, J, Delplancke, J-L, Hubin, A, Steenhaut, O, Kovacheva, D, Tatchev, D, Vassilev, Ts
• Format: Journal Article
• Language: English
• Published: 01.01.2005
• ISSN: 0013-4651
• DOI: 10.1149/1.1990124

Electroless deposition onto polycrystalline (Cu, Au) and amorphous (Ni-P) substrates was applied to prepare Co-W-P coatings of two types: crystalline (hexagonal close packed, hcp), with low phosphorus content about 2.4-2.7 atom %, and amorphous, with P concentration within 7.4-8.3 atom %. Tungsten content varied typically in the narrow range of 2.9-3.7 atom % in both types of coatings. Atomic force microscopy revealed substantial difference in their morphology. Polycrystalline Co-W-P coatings consist of grains of stacked plates (lamellas), confirmed by transmission electron microscopy also. Amorphous films are smoother and uniform. The crystalline structure promotes the surface oxidation to a higher extent than the amorphous structure, as shown by the X-ray photoelectron spectroscopy (XPS). Auger electron spectroscopy depth profiles display oxidation, smoothly diminishing toward the inside of the crystalline films. Amorphous coatings are oxidized only at the surface. Inside both types of coatings, however, all alloy components are in nonoxidized form, according to XPS data. Differential scanning calorimetry (DSC) studies of amorphous coatings revealed three transformation peaks, ascribed to a crystallization of hypoeutectic alloy and a transition of Co-based hcp phase into face-centered cubic. Magnetic properties variation with temperature is in agreement with DSC results.