Structure and phase transformation behavior of electroless Ni-P alloys containing tin and tungsten

Balaraju, JN and Jahan, SM and Jain, Anjana and Rajam, KS (2007) Structure and phase transformation behavior of electroless Ni-P alloys containing tin and tungsten. Journal of Alloys and Compounds, 436 (1-2). pp. 319-327. ISSN 0925-8388

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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.

Item Type: Article
Uncontrolled Keywords: Transition element alloys;Nanocrystal;Tungsten alloys;Tin alloys;Nickel alloys;Activation energy;Phosphorus alloys ; Differential scanning calorimetry;Scanning electron microscopy;Metallography;Thermal stability;Optical microscopy;XRD;Electrodeposition;Phase transformations
Subjects: CHEMISTRY AND MATERIALS > Chemistry and Materials (General)
Depositing User: Ms. Alphones Mary
Date Deposited: 23 Sep 2009
Last Modified: 24 May 2010 04:26

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