Papers by Author: R.K. Singh Raman

Abstract: In the present study, combinations of a Phosphonato silane DEPETES with MTEOS silane, in various ratios were applied on Mg6ZnCa alloy. The coating morphology was characterized using scanning electron microscopy (SEM) and hydrogen evolution and pH variation of the samples were studied. The results showed that the sol-gel coatings reduced the hydrogen evolution rate of the magnesium alloy in m-simulated body fluid (m-SBF) solution. Moreover, biological response like cell attachment on the coated sample was found to be enhanced considerably compared to the bare alloy

Abstract: Use of Magnesium alloys as body implants are breaking into a new paradigm of biomedical engineering as they are biocompatible, biodegradable and have mechanical properties close to that of bone. Even though corrosion fatigue (CF) and stress corrosion cracking (SCC) failures are among the most common concerns for metallic implants, CF behaviour of magnesium alloys in physiological environments has received little attention. This article reports the CF results of a common cast magnesium alloy (AZ91D) in modified simulated body fluid (m-SBF). Results showed that there was a remarkable difference in fatigue strength of Mg alloys when tests were performed in m-SBF.

Abstract: This study investigated the effects of fatigue loading and corrosive environment on bonding strength and failure modes of Carbon Fibre Reinforced Polymer (CFRP)-laminated steel. A series of tests on CFRP bonded steel plate joints was conducted. The joints were immersed in the temperature controlled sea-water with a preload. After immersions for one and six months, they were subjected to cyclic loading for a pre-set number of cycles, and then tensioned to failure. The effect of fatigue loading alone was studied by the authors in the past. In the present study, the results of the cyclic and static loading tests were compared. The comparisons between the current and previous results have provided data on the durability of CFRP/steel joints under this environmental condition.

Abstract: Chromium pre-treatments of metal have been replaced by silane pre-treatments as more environmental friendly option. Nanoparticles can be added in the silane sol-gel network have been reported to improve corrosion resistance. In this work, the electrochemical corrosion resistance of low carbon steel coated with hybrid organic-inorganic sol-gel film filled with nanoparticles was evaluated. The sol-gel films have been synthesized from 3-glycidoxy-propyl-trimethoxy-silane (3-GPTMS) and tetra-ethyl-ortho-silicate (TEOS) precursors. These films have been impregnated with 300 ppm of silica or alumina nanoparticles. The electrochemical behavior of the coated steel was evaluated by means of electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). Equivalent circuit modeling, used for quantifying the EIS measurements showed that sol-gel films containing silica nanoparticles improved the barrier properties of the silane coating. The silica nanoparticle-containing films showed highest initial pore resistance over the five days of immersion in 0.05M NaCl.

Abstract: In the present study, surface melting of a magnesium alloy, ZE41, was performed with an Nd:YAG laser, using different laser parameters (scan rate and beam type). The microstructure of the laser treated and untreated specimens were characterised by optical and scanning electron microscopy. The degree of microstructural refinement and melt depth was found to be a function of the laser scan rate. Electrochemical characterisation of the different laser treated specimens along with the untreated alloy was performed using electrochemical impedance spectroscopy. The laser treated specimens and untreated alloy showed similar corrosion resistance.

Abstract: Threshold stress intensity factor for stress corrosion cracking (K_ISCC) of AZ91D magnesium alloy in a simulated physiological environment has been determined using circumferential notch tensile (CNT) technique. Fracture surfaces of the tested specimens were analysed using scanning electron microscopy (SEM) in order to examine the features for SCC.

Abstract: Stress corrosion cracking (SCC) of a rare-earth (RE) containing and Al-free magnesium alloy, Elektron21 was studied using constant load test (CLT) in 0.1N NaCl solution saturated with Mg(OH)_2. For comparison a common Al-containing and RE-free alloy, AZ91E was investigated. In CLT the threshold stress for SCC (σ_scc) for AZ91E was found to be 60% of the yield stress, whereas Elektron21 showed immunity to SCC even at stresses in the proximity of yield stress. The susceptibility of AZ91E to SCC and immunity of Elektron21 during CLT have been confirmed by fractography.