Journal des sciences et de l'ingénierie des matériaux

Particulate reinforced aluminium matrix composites are being considered for their superior mechanical and tribological properties over the conventional aluminium alloys, and therefore, these composites have gained extensive applications in automotive and aerospace industries. In this investigation, the fabrication of 6061Al composites with different weight percentage of Al₂O₃ particles up to 0-9% was processed by liquid metallurgy route. For each composite, reinforcement particles were preheated to a temperature of 200°C and then dispersed in steps of three into the vortex of molten 6061Al alloy rather than introducing all at once, there by trying to improve wettability and distribution. Microstructural characterization was carried out for the above prepared composites by taking specimens from central portion of the casting. Microstructural characterization of the composites has revealed fairly uniform distribution of Al₂O₃ particulates. XRD analysis revealed the presence of Al₂O₃ and other phases. The tensile strength and hardness of the resultant composites were examined. It was revealed that the 6061Al- Al₂O₃ composites have a higher tensile strength than 6061 aluminium alloy with reduced ductility. It was found that an increase in the Al₂O₃ content in 6061Al alloy contributed in enhancing the hardness of the composites. The wear test was conducted using computerized pin on disc wear tester with counter surface as EN31 steel disc (HRC60) and the composite pin as specimens, demonstrated the superior wear resistance property of the composites.

Polycarbonate (PC) based composites were fabricated with different concentrations of Multi Walled Carbon Nanotubes (MWCNTs) and were subjected to dynamic impact loading using Split Hopkinson Pressure Bar (SHPB). Impact tests using this instrument were performed under varying strain rates ranging from 1096 to 4017/s on pure PC samples and samples with 0.1, 0.5 and 1% by weight of MWCNT concentrations in PC. A comparison of maximum strains produced in these samples due to different strain rates was done. It was found that the maximum strain produced for every sample increases with increase in strain rate. Maximum strain is a measure of the toughness and deformation of the sample which increases as strain rate increases.

The corrosion behaviors of two materials 316L Stainless Steel and 316LN Stainless Steel have been investigated for use as biomaterials. These samples were electrophoretically coated with Dicalcium phosphate dihydrate, and dip coated with polyvinyl alcohol. Time, current, concentration and voltage were the variables during electrophoresis. Dip coating was done for the same periods of time as was done during electrophoresis. Corrosion resistance properties were measured in Ringer’s solution by Gamry Potentiostat. The ICORR and ECORR values were estimated using Gamry Echem Software and Tafel’s extrapolation method. Coated samples were immersed in SBF solution for different periods of time, viz., 1 second, 24hours, 72hours and 1week and then further ICORR and ECORR values were estimated in Ringer’s solution. For coated samples Electrochemical Impedance Spectroscopy were also done.
Different parameters like Rp, alpha, Wd of EIS were used to evaluate the effectiveness of the coatings. Comparison of corrosion resistance among the coated samples revealed a few interesting characteristics. While DCPD coated Stainless Steel showed considerable improvement in corrosion resistance compared to as received sample, dip coated samples did not show appreciable improvement. Coated 316L shows better corrosion resistance than 316LN. Dip coated 316LN shows better corrosion resistance than 316L. So Electrophoretic Deposition gave much better coating in comparison to Dip coating. Coated samples were further studied by The Scanning Electron Microscope and Energy Dispersive X-Ray Spectroscopy. While SEM was done to ascertain uniformity of coating, EDAX was done to see the variation of calcium deposition as a function of different deposition parameters. Electrophoretic deposition gave much better coating and uniform variation of calcium compared to dip coating.

In this paper the friction wear characteristics of vinylester and vinylester composites have been investigated under dry and water lubricated sliding conditions, under different applied normal load and sliding speed. The experiments have been carried on a pin on disc arrangement at normal temperature conditions. The results showed that with increase in the applied normal load and sliding speed the coefficient of friction and specific wear rate decreases under both dry and water lubricated sliding conditions. It is also found that a thin film formed on the counterface seems to be effective in improving the tribological characteristics. The worm surface examined by SEM showed that more of the fiber exposure and fiber breakage for vinylester composite resulting higher wear rate.