Autocatalytic deposition of nananocrystalline ternary Ni-Co-P deposits: Preparation and characterization

In the present studies, electroless ternary Ni-Co-P alloy deposits were prepared in an alkaline bath and characterizations were carried out to ascertain their properties such as composition, structure, phase transformation behavior and microhardness. The effect of various anions of the metallic sources was studied on the structure and properties of the ternary deposits. The different anionic bases considered here are sulphate, chloride and sulphamate. Field emission scanning electron microscopy (FESEM) studies revealed that the morphology of the sulphate and chloride based deposits are nodular whereas the sulphamate based deposit is very fine and does not show nodularity. Energy dispersive analysis of X-ray (EDAX) results reveal medium phosphorus (5 wt.%) content in case of sulphamate based deposits whereas sulphate and chloride based deposits are found to have high phosphorus (9-12 wt.%) contents. The phase transformation behavior was studied using differential scanning calorimetry (DSC) and it was found that all the deposits exhibited three exothermic peaks. The major crystallization peak temperature of sulphamate based deposit was found to be 270°C whereas for chloride and sulphate bases it was around 355°C. X-ray diffraction (XRD) studies were carried out on the isothermally heat treated samples at their exothermic peak temperatures. The deposits are completely amorphous in as-plated condition. From the crystallization peaks, it was interpreted that metastable phosphide is present even at the annealing temperature of 475°C for sulphate and chloride based deposits and at 425°C for sulphamate based. Microhardness was tested for the as-plated as well as heat treated samples. The hardness reaches its peak of around 1000 VHN_50gf at annealing temperature of around 350°C for all the deposits. At an annealing temperature of 600°C the chloride and sulphate based deposits are found to have a good hardness of aroun- - d 850 VHN_50gf whereas for the sulphamate based deposit it drops down to 600 VHN_50gf.