S.K. Seshadri

Bio: S.K. Seshadri is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Crystallization & Nickel boride. The author has an hindex of 2, co-authored 2 publications receiving 158 citations.

Effect of coating bath composition on the properties of electroless nickel–boron films

Abstract: The effect of borohydride, thallium acetate, ethylenediamine and sodium hydroxide concentrations, and the coating bath temperature on both the coating rate and boron content of the electroless Ni–B films was investigated systematically. The Ni–B coating rate increased with the increase in thallium acetate and sodium hydroxide concentrations, but it was not very sensitive to the borohydride concentration. Below 90 g L − 1 ethylenediamine concentration the coating efficiency was significantly low and above this value as the ethylenediamine concentration increased the coating rate decreased slightly. Below 85 °C the coating rate was very low and above this temperature it was insensitive to the bath temperature. The boron content of Ni–B film increased with the increase in the borohydride concentration and the bath temperature, and decreased with the increase in thallium acetate and ethylenediamine concentrations. Up to 50 g L − 1 sodium hydroxide concentration, the boron content of the film increased and above this concentration it was insensitive to the sodium hydroxide concentration. As the boron content of Ni–B film increased, both the corrosion resistance and microhardness of Ni–B film increased. Heat treatment brought significant improvement in the microhardness but the corrosion resistance of Ni–B film was observed to decrease due to the disappearance of the amorphous characteristics of the as-deposited Ni–B film and the formation of the Ni–B compound phases.

Formation of electroless Ni-B coatings using low temperature bath and evaluation of their characteristic properties

Abstract: The formation of electroless Ni–B coatings obtained using a low temperature bath and evaluation of their characteristic properties are addressed in this paper. An alkaline bath having nickel chloride as the source of nickel and borohydride as the reducing agent was used to prepare the electroless Ni–B coatings. The influence of concentration of sodium borohydride in bath on the plating rate and the nickel/boron content of the resultant Ni–B coatings was studied. Selected coatings were characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM), respectively, for assessing the phase content, phase transformation behaviour and magnetic properties. XRD patterns reveal that the structure of electroless Ni–B coatings in as-plated condition is a function of the boron content of the coating: higher the boron content, greater the amorphous nature of the coating and vice-versa. DSC traces exhibit two exothermic peaks around 300 and 420 °C, corresponding to the phase transformation of crystalline nickel and Ni3B phases at 300 °C and the transformation of a higher phase compound to Ni3B at 420 °C. VSM studies indicate that the magnetic properties of the coating is also a function of the boron content of the coating: higher the boron content, lesser the saturation magnetization.

Mechanical properties and scratch test resistance of nickel–boron coated aluminium alloy after heat treatments

Abstract: Electroless nickel–boron deposits were synthesized on aluminium alloys and submitted to heat treatments under neutral (95% Ar + 5% H 2 ) atmosphere. Two set of treatment conditions were used: 1 h at 400 °C and 4 h at 180 °C. Micro- and nanohardness measurements were carried out on the free surface of the sample and on polished cross-sections. A comparative hardness study was conducted to assess the influence of load, indent position (free surface or cross section), and heat treatment on the results of the indentation tests. Scratch tests were made on selected coatings to assess their adhesive properties and scratch resistance. Roughness measurements were carried out on the coatings before and after heat treatments. The samples were also investigated by XRD (X-ray Diffraction), SEM (Scanning electron microscopy) and optical microscopy to link their mechanical properties to their composition, structure and morphology.