Papers by Keyword: Nanocrystalline

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Authors: O. El Kedim, M. Tachikart, Eric Gaffet
Authors: Yan Hong Ding, Ming Ji Li, Bao He Yang, Xu Ma
Abstract: The aim of this work is to present experimental results of investigation on crystallization process of Co-containing Finemet-type alloys. To different Finemet alloys, there exist different changing trends of the initial crystallization temperature after Co addition. Addition of Co in Fe73.5Cu1Nb3Si13.5B9 alloy reduces the stability of the amorphous phase, and leads to the formation of nanocrystallites at lower temperature. While adding Co increases the stability of Fe76.9Cu0.6Nb2.5Si11B9 amorphous phase, and results in higher nanocrystallites temperature. Using the method of Kissinger, possible reasons were analyzed for the variation of the apparent activation energy of crystallization determined from DSC thermograms.
Authors: Xiao Long Jiang, Y.J. Yao, M. Lai, K. Peng, Y.W. Du
Abstract: A series of nanocrystalline FeNbB films were fabricated using ion-beam sputtering technique from FeNbB target. Pieces of these films were annealed for 1 hour at various temperatures up to 5730C. Room temperature soft magnetic properties of these films were measured. The influence of microstructure on magnetic behavior in nanocrystalline FeNbB films is investigated in a series of specimens with different film’s thickness. For the sample 120nm and 5000C annealed, cutoff frequency was found to be 5E7 Hz, which has the μf0=5E10.
Authors: Pravir Polly, K. Chandra Sekhar, Balasubramanian Ravisankar, S. Kumaran
Abstract: In the present work, Al-5083-5wt% nanoyttria powders were milled for 10, 20, 30 and 35 hrs in a high energy ball milling under optimised process parameters. The milled powders were characterised by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Milled powders exhibit nanocrystalline single phase after 10hrs of milling. Consolidation of 35 hrs milled powder was done by equal channel angular pressing (ECAP) through 90o die channel angle using route A upto three passes with and without back pressure and sintered under controlled environment. Density of ECAPed samples was measured using Archimedes principle. The density is 96% for the sample consolidated with backpressure after two passes after sintering.
Authors: Hendi Saryanto, S. Khaerudini Deni, Pudji Untoro, Mat Husin Saleh, Darwin Sebayang
Abstract: The aim of this study is to determine the nanocrystalline size by using Williamson-Hall method of Fe80Cr20 powder which prepared by mechanical alloying process. X-rays diffraction line profile analysis was adopted to analyze the crystallite size and microstrains of Fe80Cr20 alloys powder. Transmission Electron Microscopy (TEM) was used to examine the microstructure morphology of the nanosized of Fe80Cr20 alloys. The crystallite size, microstrain, and lattice parameters were estimated by Williamson–Hall plot. The results showed that the mechanical alloying processes resulted the final product in nanocrystalline size range (below 12 nm) which confirmed by TEM observation and XRD line profile analysis.
Authors: Xiao Ping Li, H.L. Seet, Z.J. Zhao, Y.K. Kong
Abstract: For the purpose of developing a composite micro sensor for weak magnetic field, fabrication of high permeability ferromagnetic material is needed. The magnetic properties of the pulse-plated samples depend greatly on the chemical composition and nanocrystalline grain size of the ferromagnetic layer. In this study, the effect of the pulse plating parameter: duty cycle on the chemical composition and grain size of the deposited layer was investigated. A layer of soft ferromagnetic material Ni-Fe was deposited onto copper wires of 20µm diameter by means of pulse and dc plating and tested under XRD for grain size measurement. It was found that variations in duty cycle do not affect the thickness of the plated layer, but affect significantly the chemical composition. There is an optimum duty cycle for getting the minimum grain size of plated layer in pulse plating with saccharin. The results from the magnetic measurement showed that the permeability of the plated material increased greatly as the grain size decreased in the range of 10 – 55 nm.
Authors: Shintaro Yoshimoto, Mitsuhiro Matsuda, Michiaki Yamasaki, Yoshihito Kawamura
Authors: Srivathsan Ravi, Karthick Venkatesh Ganesh, Arunachalam Ramanathan, Jegan Annamalai, Prasanna Kumar Jaiswal
Abstract: The current research focuses on developing nano-crystalline nickel coating for engineering applications through pulse plating technique. Based on the literature survey, the current density, duty cycle and frequency were identified as important grain refining parameters. Coating was done over a mild steel sample after mechanical polishing, vapour degreasing and anodizing. Experiments were conducted using the three determining parameters and their influence on the properties of the coating was evaluated. Coatings were then characterized for the surface morphology and hardness. The XRD analysis for the surface morphology resulted in the grain size of 19 nm and the hardness measured from the microhardness tester was 677 HV which is higher than the hardness reported in the available literatures. The influence of the pulse plating parameters on the grain size and hardness of the coating has been listed out for the benefit of the scientific community.
Authors: J.M. Rigsbee
Abstract: Precipitation-strengthened Cu-based alloys have limited use as structural materials at high temperatures due to precipitate coarsening and strength loss. We have recently shown that Curefractory metal alloys produced by various physical vapor deposition methods have stable, nanocrystalline microstructures and maintain their strength properties even when annealed at temperatures as high as 900 C for up to 100 hours. This paper presents discussions of how these alloys are processed and the resulting microstructures. X-ray and electron microscopy results will be presented to document the phase transformations that occur in these alloys and result in such exceptionally stable microstructures.
Authors: Alan F. Jankowski
Abstract: Thermal anneal treatments are used to identify the temperature range of the two dominant diffusion mechanisms – bulk and grain boundary. To assess the transition between mechanisms, the low temperature range for bulk diffusion is established utilizing the decay of static concentration waves in composition-modulated nanolaminates. These multilayered structures are synthesized using vapor deposition methods as thermal evaporation and magnetron sputtering. However, at low temperature the kinetics of grain-boundary diffusion are much faster than bulk diffusion. The synthesis of Au-Cu alloys (0-20 wt.% Cu) with grain sizes as small as 5 nm is accomplished using pulsed electro-deposition. Since the nanocrystalline grain structure is thermally unstable, these structures are ideal for measuring the kinetics of grain boundary diffusion as measured by coarsening of grain size with low temperature anneal treatments. A transition in the dominant mechanism for grain growth from grain boundary to bulk diffusion is found with an increase in temperature. The activation energy for bulk diffusion is found to be 1.8 eV·atom-1 whereas that for grain growth at low temperatures is only 0.2 eV·atom-1. The temperature for transitioning from the dominant mechanism of grain boundary to bulk diffusion is found to be 57% of the alloy melt temperature and is dependent on composition.
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