The inhibiting effect of methanolic extract ofMollugo cervianaplant on the corrosion of mild steel in 1 M HCl solution has been investigated by different techniques like potentiodynamic polarization, electrochemical impedance spectroscopy, and weight loss methods for five different concentrations of plant extract ranging from 25 to 1000 mg/L. The results indicated that the corrosion inhibition efficiency increased on increasing plant extract concentration till 500 mg/L and decreased on further increasing concentration. The extract was a mixed type inhibitor with the optimum inhibition concentration of 500 mg/L in potentiodynamic polarization. The adsorption of the plant extract on the mild steel surface was found to obey Langmuir adsorption isotherm. Surface analysis was also carried out to find out the surface morphology of the mild steel in the presence and in the absence of the inhibitor to find out its efficiency. The obtained results showed that theMollugo cervianaextract acts as a good inhibitor for the corrosion of mild steel in 1 M HCl solution.

The electroless nickel composite (ENC) with various silicon carbide contents was deposited onto aluminium alloy (LM24) substrate. The wear behaviour and the microhardness of the composite coating samples were investigated and compared with particles free and aluminium substrate samples using micro-scale abrasion tester and microhardness tester respectively. The wear scar marks and wear volume were analysed by optical microscope.The wear tracks were further studied using scanning electron microscopy (SEM). The embedded particles were found to get pressed into the matrix which helps resisting further wearing process for composite samples. However, random orientation of micro cuts and micro fallow were seen for ENC sample but more uniform wearing was observed for EN sample. The composite coating with low content of SiC was worn minimum. Early penetration into the substrate was seen for samples with higher SiC content. Microhardness was improved after heat treatment for all the samples containing various SiC content. Under dry sliding condition, inclusion of particles in the matrix did not improve the wearing resistance performance in as-deposited state. The wearing worsened as the content of the particles increased generally. However, on heat treatment, the composite coatings exhibited improved wear resistance and the best result was obtained from the one with low particle contents.

The investigation is focused on the wear behaviour at elevated test temperature of composite Ni-P/SiC deposit, with varying concentration of the reinforcing SiC particles. The phase evolution measured by X-ray diffraction suggests slight crystallisation during wear testing at 200 °C. In coating without reinforcing particles, adhesive wear is accompanied by microcracks. The thermal heat generated and the cyclic loading could have induced subsurface microcracks. Owing to the effective matrix-ceramics system in composite coatings, fine grooves, abrasive polishing and uniform wearing are observed. Reinforcing particles in the matrix hinder microcrack formation and significantly reduce the wear rate. Triboxidation is confirmed from energy dispersive X-ray spectrometry.

Rajendran, R. (2013). Phase composition, microstructure and microhardness of electroless nickel composite coating co-deposited with SiC on cast aluminium LM24 alloy substrate. Surface and Coatings Technology, 235,[755][756][757][758][759][760][761][762][763] 600048, IndiaAbstract: Electroless Ni-P (EN) and composite Ni-P-SiC (ENC) coatings were developed on cast aluminium alloy substrate, LM24. The coating phase composition, microstructure and microhardness were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and microhardness tester, respectively, on as-plated and heat-treated specimens. The original microstructure of the Ni-P matrix is not affected by the inclusion of the hard particles SiC. No formation of Ni-Si phase was observed up to 500°C of heat treatment. The microhardness is increased on incorporation of SiC in Ni-P matrix. The hardening mechanism is the formation of intermetallic phase Ni3P on annealing at elevated temperature.

Three types of black anodic coatings, namely, black dyeing (BD), inorganic colouring (IC), and electrolytic colouring (EC) were prepared by conventional type II sulphuric acid anodizing on Al6061 alloys. Electrochemical behaviour of these coatings was studied by exposure to 3.5% wt sodium chloride solution for prolonged immersion periods up to 360 hours. The porous layer characteristics of all sealed, fresh and autosealed coatings were investigated by means of electrochemical impedance spectroscopy (EIS). An equivalent circuit that reproduces the a.c. impedance results of porous aluminium oxide films is proposed. The breakpoint frequency and damage function analysis were carried out to analyse the coating's electrochemical behaviour. Corrosion morphology was studied by scanning electron microscopy. It was observed that BD and IC behaved in a very similar manner to sulphuric acid anodising (SAA). However EC was behaving in an entirely different manner. Among all colouring methods BD was showing very less values. All these findings were further confirmed by linear polarisation studies. No major evidence of localised corrosion or pitting of the black anodic coatings was observed in SEM micrographs.