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Autocatalytic ternary Ni-Sn-P, Ni-W-P and quaternary Ni-W-Sn-P films were prepared using alkaline citrate-based baths and compared with binary Ni-P coatings. Energy dispersive analysis of X-ray (EDAX) showed that binary Ni-P deposit contained 11.3 wt.% of phosphorus. Codeposition of tungsten in Ni-P matrix resulted in ternary Ni-W-P with 5 wt.% P and 7.8 wt.% of tungsten. Incorporation of tin led to ternary Ni-Sn-P deposit containing 0.4 wt.% Sn and 10.3 wt.% P. Presence of both sodium tungstate and sodium stannate in the basic bath had resulted in quaternary coating with 6.9 wt.% W, traces of Sn and 6.4 wt.% P. X-ray diffraction patterns of all the deposits revealed a single, broad peak which showed the nanocrystalline nature of the deposits. For the first time in related literature, the presence of a metastable phase Ni12P5 in ternary deposits is reported in the present study. Metallographic cross-sections of all the deposits revealed the banded/lamellar structure. Scanning electron microscopy (SEM) studies of the deposits showed smooth nodules for ternary deposits, but coarse and well-defined nodules for quaternary deposits. DSC studies of phase transformation behavior of the ternary Ni-Sn-P deposit revealed a single sharp exothermic peak at 365 xB0;C. However, ternary Ni-W-P and quaternary Ni-W-Sn-P deposits exhibited a low temperature peak at 300 xB0;C, a split type high temperature peak at 405 and 440 xB0;C and a very high temperature peak at 550 xB0; C. Higher activation energy values were obtained for W-based alloy deposits. Presence of W and Sn has helped to retain high microhardness values even at higher temperatures indicating an improved thermal stability.

An attempt has been made to deposit ternary Ni–W–P coatings autocatalytically using nickel sulphamate and sodium tungstate as nickel and tungsten sources, respectively, and sodium hypophosphite as a reducing agent. These coatings were deposited using an alkaline citrate based bath and were compared with plain Ni–P coatings. Both deposits were characterized for their structure, morphology, crystallization behavior and microhardness. Results obtained from EDX analysis showed that binary Ni–P alloy contains 11.0 wt.% of phosphorus. Incorporation of tungsten (2.7 wt.%) had reduced the phosphorus content to about 3.5 wt.% in ternary Ni–W–P deposits. Apart from phosphorus and nickel contents, a trace of sulphur was noticed in ternary Ni–W–P deposit. Structural examination carried out by XRD studies revealed the presence of a broad peak with a calculated grain size of 1.2 nm for binary alloy, where as a sharp peak with a grain size of 10 nm is obtained for ternary Ni–W–P alloy. Optical micrographs of as-plated binary Ni–P alloys exhibited slightly nodular structure compared to coarse nodular structure of ternary Ni–W–P deposits. Etched metallographic cross-sections revealed a lamellar/banded structure in both deposits. Studies on phase transformation behavior carried out by DSC showed that the crystallization temperature for ternary alloys was higher compared to binary alloys. Calculated activation energies for Ni–P and Ni–W–P deposits were 229 and 289 kJ/mol, respectively. Microhardness measurements made on as-plated and heat-treated (400 °C for 1 h) deposits showed higher hardness values for ternary Ni–W–P deposits compared to binary deposits.