Study on the Effect of the Thiourea on Nano-Mechanical Properties and Microstructures of the Electroformed Thin Ni-P Foil

The effect of thiourea on the nano-mechanical and chemical properties of Ni-P foil was studied to develop a high performance Ni-P deposit for automobile and machinery parts. The Ni-P deposit was prepared by electroforming in a modified sulphate bath with different amounts of thiourea. Chemical analysis of the electrodeposited Ni-P foils by energy dispersive spectroscopy showed that phosphorous in the foil was reduced with thiourea. Structural analysis by X-ray diffractometry revealed that the (111) plane of the Ni-P deposits grew preferentially with increasing crystallinity. Surface analysis by atomic force microscopy and field-emission scanning electron microscopy showed that the surfaces of the Ni-P electrodeposited with 0 and 0.01 g/L thiourea were relatively smooth and clean showing no nodules, whereas, the cauliflower-like nodules were observed on the surfaces of the deposits prepared with 0.03, 0.05, 0.07 and 0.1 g/L thiourea. The surface roughness (RRMS) of the deposits increased by addition of 0.1 ppm of thiourea from 6 to 54 nm. Nano-mechanical properties of the Ni-P foil such as elastic modulus, hardness and stiffness determined by tribonano-indenter were tended to increase by addition of 0.1 ppm of thiourea from 77 to 156 GPa, 6.6 to 8.9 GPa and 109.6 to 186.6 µN/nm, respectively. Key words: electrodeposition, Ni-P, thiourea