Browsing by Author "Singh, R"

Now showing 1 - 3 of 3
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    Critical deposition height for sustainable restoration via laser additive manufacturing
    (Springer Nature, 2013-10-03) Paul, S; Singh, R; Yan, W; Samajdar, I; Paradowska, AM; Thool, K; Reid, M
    Laser material deposition based restoration of high-value components can be a revolutionary technology in remanufacturing. The deposition process induces residual stresses due to thermomechanical behavior and metallurgical transformations. The presence of tensile residual stresses in the deposited layer will compromise the fatigue life of the restored component. We have developed a novel fully coupled metallurgical, thermal and mechanical (metallo-thermomechanical) model to predict residual stresses and identified a critical deposition height, which ensures compressive residual stresses in the deposited layer. Any lower deposition height will result in tensile residual stresses and higher deposition height will result in excessive dilution (substrate melting). We have validated the model using neutron and micro-focus X-ray diffraction measurements. This study highlights that the critical deposition height corresponds to the minimum cooling rate during solidification. It addresses one of the major outstanding problems of additive manufacturing and paves a way for “science-enabled-technology” solutions for sustainable restoration/remanufacturing. © 2021 Springer Nature Limited
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    Effect of Cr and Zr addition on oxidation resistance of nanocrystalline Fe-Cr-Ni-Zr
    (Curran Associates, Inc., 2011-11-20) Venkataraman, MB; Singh, R; Atanacio, AJ; Fu, J; Koch, CC
    The effect of nanocrystalline grain size and alloying additions of Cr, Ni and Zr on the oxidation resistance of nanocrystalline Fe-based alloys has been investigated. Bulk nanocrystalline alloy pellets, having composition Fe-xCr-5Ni-2Zr and Fe-xCr-5Ni {x = 7, 10} were prepared by a mechanical alloying and compaction route. A novel multi-step hot-compaction process has been investigated for the consolidation of powders into close-to-100% dense nc pellets (grain size 60-70 nm). The pellets showed high hardness (7.5-8.0 GPa) and reasonable ductility under shear stress condition. The high temperature oxidation resistance of these alloys, at 550 °C, has been compared with conventional microcrystalline stainless steel alloy. Nanocrystalline grain size was found to improve the oxidation resistance particularly in the alloys with lower Cr content. This behaviour is attributed to the greater grain boundary diffusivity of Cr in the nanocrystalline alloys. Zr addition was found to improve the thermal stability and insignificantly influence the oxidation resistance. © 2011 Australasian Corrosion Association
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    Role of micro-/nanocrystalline structure in oxidation of Fe-Cr alloys
    (Curran Associates, Inc., 2008-11-16) Singh, R; Gupta, RK; Atanacio, AJ; Koch, CC
    A simplistic approach would suggest a greater corrosion rate of an alloy in its nanocrystalline state than in microcrystalline state, due to a larger fraction of grain boundaries (i.e., high energy area) in the former. However, the nature of influence of nanostructure on corrosion does not seem to be similar in all cases. The nature of the influence can be opposite, depending on the type of corrosion and environment-material system. A considerably improved corrosion resistance of an Fe-C alloy in the nanocrystalline state (as opposed that in the microcrystalline state) has been established.Copyright© (2008) by the Australasian Corrosion Association