Engineering topics

Pradhan, S. K.

Publications and source records attributed to Pradhan, S. K..

5 records

DOE OSTI2018

Corrosion-Resistant Hydrophobic Nanostructured Ni-Reduced Graphene Oxide Composite Coating with Improved Mechanical Properties

In the present work, corrosion-resistant and hydrophobic nickel-reduced graphene oxide (Ni-RGO) composite coating prepared by electroless deposition technique on mild steel (MS), without the use of toxic chemicals, is reported. The field emission scanning electron microscopy micrographs show a uniform composite coating of Ni-RGO with smaller grain size, whereas cuboidal and larger grains were observed in the case of Ni coating on MS. A reduction in crystallite size from 30 to 13 nm with the incorporation of RGO to the Ni matrix was estimated from XRD. The corrosion activity was investigated with potentiodynamic polarization and electrochemical impedance spectroscopy measurements. The surface of Ni-RGO composite coating remained intact, almost undamaged and showed a robust resistance to corrosion with an inhibition efficiency of about 95% in aggressive 3.5 wt.% NaCl solution. Nanoindentation test revealed that the hardness and Young’s modulus of Ni-RGO composite coating are increased by about 25 and 19%, respectively, as compared to Ni coating.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2018

Microstructure evolution during low-strain thermo-mechanical processing and its repercussion on intergranular corrosion in alloy 600H

Highlights: • GBE microstructure in alloy 600H is realized through the sole activation of SIBM. • Higher TRD size and lower fractal dimension are characteristics of GBE microstructure. • Partially/fully recrystallized specimen shows higher DOS than as-received condition. • GBE specimen shows remarkable resistance against percolation and grain dropping. • Extent of percolation is governed by residual strain and random HAGBs connectivity. - Abstract: The current investigation deals with the evolution of microstructures as a consequence of varying processing parameters viz. extent of deformation, annealing temperature and time during grain boundary engineering (GBE) type thermo-mechanical processing in alloy 600H. Furthermore, the influence of the various product microstructures (viz. partially recrystallized, fully recrystallized and GBE) on intergranular corrosion is evaluated and compared with the as-received condition. Detailed characterization of the as-processed specimens have revealed that lower extent of deformation (7.5%) followed by a longer annealing treatment (i.e. 60 min) at a higher temperature (1373 K) could lead to a GBE microstructure with a higher proportion of Σ3{sup n} boundaries (~72%) due to the predominant activation of multiple twinning. In contrast, the specimens associated with moderately higher extent of deformation (10% and 15%) have revealed the occurrence of static recrystallization. The GBE specimen has demonstrated an excellent resistance against percolation essentially due to its discontinuous random high angle boundaries (HAGBs) network. In contrast, the nucleation of the finer grains in the recrystallized specimens caused the regeneration of random HAGBs network (as substantiated by the fractal analysis) that leads to higher percolation and severe grain dropping. In spite of the similar grain boundary character distribution, the severity of corrosion is relatively lesser in the as-received condition than the completely recrystallized specimen owing to its coarse-grained microstructure that commendably retarded the diffusion of chromium from the grain interior to the boundary.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Structural and magnetic properties of La2Ni1−xCoxMnO6 compounds

Highlights: • Monoclinic La2Ni1−xCoxMnO6 samples have been prepared using Sol-gel technique. • Rietveld analysis shows an octahedrally distorted double perovskite structure. • The nature of FM interaction and TC depend on the B-site ions. • The short range FM ordering above TC is induced by antisite disorders. • The existence of any spin glass like phase in such system is discarded. - Abstract: Single phase monoclinic La{sub 2}Ni{sub 1−x}Co{sub x}MnO{sub 6} (x = 0.2, 0.4, 0.8) compounds, henceforth, referred as LNC{sub x}MO (x = 0.2, 0.4, 0.8) have been prepared by Sol–gel technique. The structural study and redox titration suggest that the samples are both La and O deficient. The generated atomic models using Rietveld refined structural parameters show octahedral distortion in the double perovskite structure. X-ray photoelectron spectroscopy (XPS) study has been used to determine the predominant valence states of Ni, Mn and Co ions. LNC{sub x}MO (x = 0.2, 0.4) are found to be Heisenberg ferromagnets whereas LNC{sub 0.8}MO is a phase segregated system. In LNC{sub 0.4}MO and LNC{sub 0.8}MO, at temperatures above T{sub C}, χ{sup −1}(T) curve shows the characteristics of Griffiths phase. The study of ac susceptibility and isothermal remanent magnetization (IRM) discard the possibility of any glassy state at low temperatures. The antiphase boundaries (APBs), antisite disorders (ASDs) and oxygen vacancies play important roles in this system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2017

Through-thickness microstructural evolution during grain boundary engineering type thermomechanical processing and its implication on sensitization behavior in austenitic stainless steel

Highlights: • GBE-treated 304L steel exhibits thickness-dependent microstructural evolution. • Degree of sensitization increases from surface to interior in GBE specimen. • Low fractal dimension and large TRD size lead to lesser sensitization at surface. • As-received specimen shows high albeit thickness-independent sensitization behavior. • Higher residual strain leads to higher sensitization at surface of deformed sample. - Abstract: Through-thickness microstructural variations and their synergistic influence on degree of sensitization in grain boundary engineering (GBE) treated 304L stainless steel was compared with solution-annealed and marginally cold-worked (~ 3% thickness reduction) specimens. The solution-annealed specimen has shown higher degree of sensitization due to the presence of lower fraction of Σ3 (as well as other low Σ CSL) boundaries and dominant random high-angle boundaries (RHAGBs) connectivity. However, it has shown thickness-independent sensitization behavior as grain boundary character distribution, residual strain and grain boundary network topology towards thickness direction are similar. Owing to higher residual strain, as revealed by local misorientation analysis, the cold-worked specimen showed maximum degree of sensitization (higher than solution-annealed condition) at surface. The GBE specimen has shown much lower degree of sensitization at surface due to higher-fraction of Σ3 boundaries and discontinuous RHAGBs connectivity. However, increasing fraction of RHAGBs and their connectivity, as confirmed by twinning-related domain and fractal analysis, cause more sensitization at interior of this specimen. In spite of this, the degree of sensitization at the interior of GBE specimen is lower than the solution-annealed or cold-worked specimen. Even though the residual strain in GBE specimen is higher than the solution-annealed condition, the lower degree of sensitization indicates that the grain boundary character distribution and grain boundary network topology have higher implication than residual strain in controlling sensitization.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Conductivity enhancement in mechanosynthesized Bi{sub 2}O{sub 3}

Nanostructured Bi{sub 2}O{sub 3} was prepared through mechanical alloying method. Detailed microstructural information was obtained after Rietveld refinement of the prepared samples. The Transmission Electron Microscope images confirmed the crystallinity of the sample. The average crystallite size decreases whereas microstrain increases due to milling. The ionic conductivity of the milled sample was found to have increased few orders than the unmilled sample. The change in structural and electrical properties due to milling were discussed and correlated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗