Search

Abstract: Microstructural, corrosion and nanomechanical behaviour of micro arc oxidised (MAO) coating grown on magnesium AZ31B alloy was evaluated. Microstructural characterization of the coating was carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM) followed by image analysis and energy dispersive spectroscopy (EDX). Linear polarization technique was used to evaluate the corrosion behaviour of the MAO coating. Further, nanoindentation was employed to evaluate nanohardness and Young’s modulus of the MAO coating. The characteristic values of both the nanohardness and the Young’s modulus were calculated through the application of the Weibull statistics. [Copyright &y& Elsevier]

Abstract: The motivation behind this study was the urge to understand how the high strain rate flyer plate impact affects the nanohardness of alumina ceramics. Therefore, the load controlled nanoindentation experiments were conducted with a Berkovich indenter on an as received coarse grain (~10μm), high density (~3.98g.cm3) alumina and the shock recovered tiny fragments of the same alumina. The shocked alumina fragments were obtained from an earlier flyer plate shock impact study in a two stage gas gun. The nanohardness of the as received alumina was much higher than that of the shocked alumina. The shocked alumina showed a relatively much stronger indentation size effect (ISE) while the as received alumina exhibited a mild ISE. A new explanation was given for the presence of the relatively strong ISE in the shock recovered alumina. Additional characterizations such as scanning electron microscopy, field emission scanning electron microscopy, transmission electron microscopy and analysis of the experimental load depth data were utilized for this purpose. Finally, a new, qualitative model was proposed to provide a rational picture of the nanoindentation responses of the as received and shocked alumina ceramics. [Copyright &y& Elsevier]

Present study reports the detailed nanomechanical and corrosion behaviours of crystalline and amorphous plasma electrolytic oxidation (PEO) coatings developed on Aluminium alloy-6061. The concentration of sodium silicate in the electrolyte is tailored to achieve crystalline and amorphous natures of the PEO coatings. X-ray diffraction (XRD), scanning electron microscopy (SEM) and nanoprofilometry techniques are utilized to investigate microstructural and morphological properties of the PEO coatings. XRD studies confirmed that crystalline ceramic phases are obtained at lower silicate concentration while amorphous nature occurred for comparatively higher concentration of silicate in the electrolyte. Nanoindentation technique is utilized to study the mechanical properties such as hardness (H) and Young's modulus (E) of the PEO coatings. The scatter of the data is treated with well-established Weibull statistical method. Finally, in depth corrosion behaviour of the coatings are investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. Amorphous coatings exhibited superior mechanical properties compared to the crystalline coatings. This is possibly linked with the presence of aluminosilicate phases and difference in silicon content in the coatings. However, as expected crystalline PEO coatings offer better corrosion resistance than the amorphous coatings and this behaviour is explained in terms of porosity contents of the coatings. [ABSTRACT FROM AUTHOR]