Papers by Author: Narasimalu Srikanth

Abstract: Two new AZ31 nanocomposites containing Al2O3 nanoparticle reinforcement were fabricated with different reinforcement integration methods using solidification processing followed by hot extrusion. Each nanocomposite had similar composition (Al and Zn contents), microstructure (grain and intermetallic particle sizes, Al2O3 nanoparticle distribution) and hardness. However, the first nanocomposite had better overall tensile properties compared to the second nanocomposite. Also, the second nanocomposite exhibited better overall compressive properties compared to the first nanocomposite. On the whole, the second nanocomposite was more deformable in tension and compression than the first nanocomposite. The effect of reinforcement integration method on the tensile and compressive properties of the AZ31- Al2O3 nanocomposites is investigated in this paper.

Abstract: New bimetal magnesium/aluminium macrocomposites containing millimeter-scale Al based core reinforcement were fabricated using solidification processing followed by hot coextrusion. The initial macrocomposite consisted of a combination of pure Mg shell and pure Al core. Some problems encountered with the macrocomposite were Mg and Al grain coarsening, an inadequate Mg-Al interface (macrointerface) and consequent reduction in strength, compared to monolithic Mg. To rectify these problems, three approaches were taken in the following order primarily to widen (strengthen) the Mg-Al interface: (a) pouring of pure Al at 900°C (higher temperature approach), (b) pure Mg shell substitution with AZ31 shell (single substitution approach) and (c) pure Mg shell and pure Al core substitution with AZ31 shell and AA5052 core, respectively (double substitution approach). The evolution (strengthening) of the Mg-Al interface and its effect on microstructure and mechanical properties in each macrocomposite is investigated in this paper.

Abstract: In the present study, elemental Ni powder was mechanically milled (MMed) for 10 hours to reduce the grain (crystalline) size in the nano-range (<100nm). The mechanically milled powder (10h-MMed) was consolidated by die-cold compaction and was further hot extruded at high temperatures to maintain a crystallite size within the nano range. Further, the specimen was tested by a novel free-free type suspended beam arrangement, coupled with circle-fit approach to determine damping characteristics. To vary the resonant frequency of the suspended beam, end masses with different weights were added. The characterization results revealed that the nano-size grains exhibit increased damping compared to a coarse-grained sample, under similar vibration frequency. Results also show that the damping capacity of both nano and coarse grained samples decreases with an increase in frequency of vibration. Particular emphasis was placed to correlate the damping capacity with the process induced residual stresses present in the samples.