• A K Singh

      Articles written in Bulletin of Materials Science

    • Analysis of stainless steel samples by energy dispersive X-ray fluorescence (EDXRF) spectrometry

      M K Tiwari A K Singh K J S Sawhney

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      A simple method for the analysis of stainless steel samples is presented which is based on radioisotope excited energy dispersive X-ray fluorescence (EDXRF) spectrometry and does not require any type-standards. Both absorption and enhancement effects have been taken into account in the fundamental parameter method for quantitative analysis and an iterative approach is followed for calculation of concentrations in steel samples. Non-linear least square fitting (NL-LSF) procedures have been used to determine accurately the fluorescent peak intensities. The method has been tested by analysing several CRM standard reference samples and 304 and 316 steel samples assuming as unknown. The EDXRF results have also been compared with the results of analysis of same samples by vacuum emission spark spectrometry (VES). Obtained values for concentration in steel samples match quite well with their certified values.

    • Preparation and thermomechanical properties of stir cast Al–2Mg–11TiO2 (rutile) composite

      S K Chaudhury A K Singh C S S Sivaramakrishnan S C Panigrahi

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      Al–2Mg–11TiO2 composite was successfully prepared by the conventional vortex method. The macrostructural observation revealed columnar structure with rutile particles being distributed throughout the matrix in the form of agglomerates. Microstructural observation showed the presence of micro voids in the particle-enriched zone. Electrical resistivity measurement showed a phase transformation at 360°C, which was consistent during DSC studies due to the precipitation of TiAl3 phase. As-cast composite was both hot rolled and cold rolled successfully to 50 and 40% reduction, respectively. The mechanical properties of the thermomechanically-worked composite were studied. From fractographic analysis, it was clear that the crack had nucleated at the particle/matrix interface and propagated through the matrix by microvoid coalescence. Ultimate tensile strength of cold worked composite was found to be better than the hot worked material.

    • Surface hardness behaviour of Ti–Al–Mo alloys

      Raja Ram Prasad Shankar Azad A K Singh R K Mandal

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      The microhardness characteristics of various micro-constituents formed in the Ti–Al–Mo alloys have been investigated. Four alloys having compositions, Ti–40Al–2Mo, Ti–42Al–2Mo, Ti–40Al–6Mo and Ti–42Al–6Mo, have been chosen for this purpose. All of these were heat treated at 1300°C and 1400°C for 1 h and water quenched. All the specimens after above heat treatments have displayed load independent Vickers hardness values (VHN) around 300 g of applied load. The average surface hardness characteristic of the alloys is largely found to be dictated by the phases that are present. The microstructural specific VHN values vary between 600 and 750. The indentation behaviour, however, is governed by the morphologies and length scales of microstructures. The most remarkable finding of the present study pertains to the formation of shear bands around the periphery of the indenter for a finer basket weave microstructure in the Ti–40Al–2Mo. The cluster of finely located slip steps was clearly seen. Such a report is lacking in literature in this class of alloys.

    • Effect of thermomechanical processing on evolution of various phases in Ti–Nb alloys

      S Banumathy K S Prasad R K Mandal A K Singh

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      This paper deals with the effect of thermomechanical processing on microstructural evolution of three alloys, viz. Ti–8Nb, Ti–12Nb and Ti–16Nb. The alloys were hot rolled at 800°C and then subjected to various heat treatments. Samples from hot-rolled alloys were given solution-treatment in 𝛽 and 𝛼 + 𝛽 phase fields, respectively followed by water quenching and furnace cooling. The solution-treated alloys were subsequently aged at different temperatures for 24 h. Phases evolved after various heat treatments were studied using X-ray diffractometer, optical, scanning and transmission electron microscopes. The alloy Ti–8Nb exhibits 𝛼 and 𝛽 phases while the alloys Ti–12Nb and Ti–16Nb show the presence of 𝛼'', 𝛽 and 𝜔 phases in the as-cast and hot-rolled conditions. The 𝛽 solution treated and water quenched specimen of the alloy Ti–8Nb displays 𝛼'' phase while the alloys Ti–12Nb and Ti–16Nb exhibit 𝛼'', 𝛽 and 𝜔 phases. The alloy Ti–8Nb shows the presence of 𝛼, 𝛽 and 𝜔 phases while those of Ti–12Nb and Ti–16Nb display the presence of 𝛼, 𝛼'', 𝛽 and 𝜔 in 𝛼 + 𝛽 solution treated and water quenched condition. The observation of 𝜔 phase in solution treated condition depends on the cooling rate and the Nb content while in the aged specimens, it is governed by aging temperature as well as the Nb content.

    • Mobilities and dislocation energies of planar faults in an ordered A3B (D019) structure

      A K Singh R Sankarasubramanian T K Nandy

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      Present work describes the stability of possible planar faults of the A3B (D019) phase with an axial ratio less than the ideal. Mobilities and dislocation energies of various planar faults viz. antiphase boundaries (APBs), superlattice intrinsic stacking faults (SISFs) and complex stacking faults (CSFs) have been computed using complex fourth-order tensor transformations and hard sphere model. Displacements normal to the slip planes for various slip systems (vertical shift) have been used to calculate mobility of dislocations. The energy of the planar faults in Ti3Al intermetallic is calculated using some simplifying assumptions. Based on the mobility and energy, stability of planar faults has been explained. These results are compared with single crystal ordered Ti3Al alloy having D019 structure.

    • Synthesis of Fe–Si–B–Mn-based nanocrystalline magnetic alloys with large coercivity by high energy ball milling

      P D Reddi N K Mukhopadhyay B Majumdar A K Singh S S Meena S M Yusuf N K Prasad

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      Alloys of Fe–Si–B with varying compositions of Mn were prepared using high energy planetary ball mill for maximum duration of 120 h. X-ray diffraction (XRD) analysis suggests that Si gets mostly dissolved into Fe after 80 h of milling for all compositions. The residual Si was found to form an intermetallic Fe3Si. The dissolution was further confirmed from the field emission scanning electron microscopy/energy dispersive X-ray analysis (FE-SEM/EDX). With increased milling time, the lattice parameter and lattice strain are found to increase. However, the crystallite size decreases from micrometer (75–95 𝜇m) to nanometer (10–20 nm). Mössbauer spectra analysis suggests the presence of essentially ferromagnetic phases with small percentage of super paramagnetic phase in the system. The saturation magnetization (𝑀s), remanance (𝑀r) and coercivity (𝐻c) values for Fe–0Mn sample after 120 h of milling were 96.4 Am2/kg, 11.5 Am2/kg and 12.42 k Am-1, respectively. However, for Fe–10Mn–5Cu sample the 𝑀s, 𝐻c and 𝑀r values were found to be 101.9 Am2/kg, 10.98 kA/m and 12.4 Am2/kg, respectively. The higher value of magnetization could be attributed to the favourable coupling between Mn and Cu.

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