• N K Mukhopadhyay

      Articles written in Bulletin of Materials Science

    • Role of aluminium addition on structure of Fe substituted Fe73.5−𝑥Si13.5B9Nb3Cu1Al𝑥 alloy ribbons

      Gautam Agarwal Himanshu Agrawal M Srinivas B Majumdar N K Mukhopadhyay

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      The investigation has dealt with the structure and magnetic properties of rapidly solidified and annealed Fe73.5−𝑥Si13.5B9Nb3Cu1Al𝑥 (𝑥 = 0, 2, 4, 6 at%) ribbons prepared by melt spinning. Complete amorphous structure was obtained in as-spun ribbons of 𝑥 = 0 and 2 at% compositions, whereas structure of ribbons containing higher Al was found to be partially crystalline. Detailed thermal analyses of the alloys and the melt spun ribbons revealed that the glass forming ability in the form of 𝑇x/𝑇l (ratio between crystallization and liquidus temperature) is the highest for 2 at% Al alloys and decreases with further addition of Al. Annealing of all as spun ribbons resulted in the precipitation of nanocrystalline phase embedded in amorphous matrix in the form of either 𝐷𝑂3 phase or 𝑏𝑐𝑐 𝛼-Fe(Si/Al) solid solution depending on the initial composition of the alloy. Only 𝑏𝑐𝑐 𝛼-Fe(Si/Al) solid solution was formed in 2 at% Al ribbons whereas ordered DO3 structure was found to be stabilized in other ribbons including 0 at% Al. A detailed study on determination of precision lattice parameter of nanocrystalline phase revealed that the lattice parameter increases with the addition of Al indicating the partitioning behaviour of Al in nanocrystalline phase.

    • 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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