PHASE TRANSFORMATION BEHAVIOUR OF ELECTROLESS NI-MO-P ALLOY COATINGS

Engineering applications for electroless nickel can be found in virtually every industry. Various physical characteristics of electroless nickel coatings such as hardness, uniformity, and corrosion resistance, as well as the ability to plate nonconductive surfaces make this coating surfaces of choice for many engineering applications. In the present investigation, the preparation and characterization of electroless plain Ni-P and Ni-Mo-P coatings was carried on mild steel with 0.13% of C, 0.18% Mn, 0.1% Si, 99.59% Fe (wt%) dimension of 2.5cmX2.5cmX0.8cm with roughness (Ra=0.5µm) to understand the material performance. The investigation included electroless Ni-P and Ni-Mo-P matrix using two different types of baths. Bath 1 of Ni-P bath uses nickel sulphate as nickel source, while sodium hypophosphite served as the reducing agent and source of phosphorus. Whereas the second bath of Ni-Mo-P had sodium molybdate used as a source of molybdenum along with suitable amounts of complexing agents and stabilizers. The bath 1 was operated at a pH range of 8±0.2 with temperature of 80±2°C. The bath 2 was operated at a pH range of 11±0.2 with temperature of 85±2°C. Elemental compositions of the deposits were examined by means of scanning electron microscope (SEM, Model Leo 4401) with EDAX attachment to determine the Mo and P elements co-deposited in EN matrix. From EDAX analysis, the sample exhibited Ni-P deposit containing 12.75% P and 87.25% Ni and the Ni-Mo-P deposit consists of 1.09% P, 16.25% Mo and 82.66% Ni. DSC thermograms showed that the crystallization temperature obtained for Ni-P coating was 357C and for Ni-Mo-P coating 515C. The activation energy for the crystallization of Ni-P and Ni-Mo-P deposits were 220 kJ/mol and 111 kJ/mol, respectively