Browsing by Author "Mara, NA"

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    Effect of double ion implantation and irradiation by Ar and He ions on nano-indentation hardness of metallic alloys
    (Elsevier, 2013-07-01) Dayal, P; Bhattacharyya, D; Mook, WM; Fu, EG; Wang, YQ; Carr, DG; Anderogluc, O; Mara, NA; Misra, A; Harrison, RP; Edwards, L
    In this study, the authors have investigated the combined effect of a double layer of implantation on four different metallic alloys, ODS steel MA957, Zircaloy-4, Ti–6Al–4V titanium alloy and stainless steel 316, by ions of two different species – He and Ar – on the hardening of the surface as measured by nano-indentation. The data was collected for a large number of indentations using the Continuous Stiffness Method or “CSM” mode, applying the indents on the implanted surface. Careful analysis of the data in the present investigations show that the relative hardening due to individual implantation layers can be used to obtain an estimate of the relative hardening effect of a combination of two separate implanted layers of two different species. This combined hardness was found to lie between the square root of the sum of the squares of individual hardening effects, (ΔHA2 + ΔHB2)0.5 as the lower limit and the sum of the individual hardening effects, (ΔHA + ΔHB) as the upper limit, within errors, for all depths measured.© 2013, Elsevier B.V.
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    Large strain deformation of bimodal layer thickness Cu/Nb nanolamellar composites
    (Elsevier, 2013-03-01) Wynn, TA; Bhattacharyya, D; Hammon, DL; Misra, A; Mara, NA
    Nanolayered composites have garnered much attention due to their ability to withstand deformation to large strains, shock deformation, and irradiation induced microstructural damage. These behaviors have been attributed to high densities of bimetal interfacial content. Although they exhibit yield strengths approaching theoretical limits, multilayered materials with layer thicknesses less than 10 nm have shown limited ductility in rolling. In this study, bimodal 4 nm/40 nm Cu/Nb multilayers are rolled to 30% thickness reduction without the onset of shear instability. The stacking order used allows focus to be drawn specifically to the ductility by the boundary crossing mechanism exhibited in multilayered materials with layer thicknesses below 10 nm. Through the geometric constraint offered by alternating 4 nm and 40 nm layer thickness modes, the onset of localized shear is avoided and the 4 nm layers can be rolled to large strains. © 2015, Elsevier B.V.