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The corrosion behavior of a Zirconium-based bulk metallic glass subjected to friction stir processing was evaluated. Processing was done at the tool rotational speeds of 300 rpm, 500 rpm and 900 rpm. Potentiodynamic polarization and electrochemical impedance spectroscopy studies were carried out in 0.1 M NaCl solution. A strong correlation was found between the corrosion rate and enthalpy of structural relaxation, which is a measure of free volume. Electrochemical impedance spectroscopy measurements showed lower polarization resistance for processed samples as compared to as-cast metallic glass which is consistent with the DC polarization results. Shear bands in processed specimens were found to be preferred nucleation sites for the formation of corrosion pits. In contrast, pitting was more stochastic for the as-cast metallic glass. [ABSTRACT FROM AUTHOR]

Friction stir processing (FSP) was carried out for AE42 Mg alloy resulting in significant grain refinement and uniform dispersion of fine in situ precipitates. The average grain size was 20 μm for the as-cast AE42 alloy, which was refined to 1.5 μm after FSP. Tensile testing revealed significantly higher modulus and yield strength for the friction stir processed (FSPed) specimen with some improvement in ductility. The fractured surface of the as-cast alloy showed ridges, grooves and cracks indicating brittle failure. In contrast, the fractured surface of FSPed specimen showed fine dimples, characteristic of ductile failure. Nano-indentation was used to analyze the variation of hardness and modulus across the nugget zone of the FSPed specimen. FSPed specimen demonstrated greater strain-hardening tendency compared to the as-cast alloy. Enhancing the mechanical properties of Mg alloys can result in substantial cost savings across a number of industries and have wide economic impact. [ABSTRACT FROM AUTHOR]

Friction stir processing (FSP) of Mg based AE42 alloy was performed under single pass as well as double pass conditions. The evolution of microstructure was investigated using electron back scatter diffraction (EBSD) analysis. EBSD revealed that the grain size and texture varies within the nugget zone of friction stir processed region. The variation of mechanical properties across the nugget region was evaluated using nanoindentation. Hardness and Young's modulus was found to increase along the depth of the friction stir processed specimen. This was attributed to a finer grain structure with increasing depth. The friction stir processed specimen showed higher tendency toward strain hardening compared to as-cast alloy. Understanding microstructure-property relationship paves the way for optimization of FSP conditions and development of advanced functional Mg alloys. [ABSTRACT FROM AUTHOR]

Cavitation erosion remains the primary cause of material degradation in fluid machinery components operating at high speed. Micro-jets/shock waves caused by implosion of bubbles on material surface results in significant material loss and premature failure of the components. The presence of corrosive medium further exuberates this effect, causing rapid degradation. Here, we demonstrate a novel pathway to control cavitation erosion-corrosion by tailoring the surface properties using submerged friction stir processing (FSP), a severe plastic deformation process. FSP parameters were varied over wide range of strain-rates to generate tailored microstructures. High strain-rate processing resulted in nearly single phase fine grained structure while low strain-rate processing resulted in phase transformation in addition to grain refinement. As-received and processed samples were subjected to ultrasonic cavitation in distilled water as well as in corrosive environment of 3.5% NaCl solution. Individual roles of cavitation erosion, corrosion and their synergistic effects were analyzed. Depending on the microstructure, processed samples showed nearly 4–6 times higher cavitation erosion resistance compared to as-received alloy. Superior cavitation erosion-corrosion resistance of processed samples was attributed to surface strengthening, higher strain-hardening ability and quick passivation kinetics. The results of current study could be potentially transformative in designing robust materials for hydro-dynamic applications. [ABSTRACT FROM AUTHOR]