The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

J Eckert - One of the best experts on this subject based on the ideXlab platform.

  • designing bulk metallic glass and glass Matrix composites in martensitic alloys
    Journal of Alloys and Compounds, 2009
    Co-Authors: J Das, Simon Pauly, M Bostrom, Karsten Durst, Mathias Goken, J Eckert
    Abstract:

    Abstract To circumvent the limited plasticity of bulk metallic glasses (BMGs), heterogeneous materials with glassy Matrix and different type and length-scale of heterogeneities (micrometer-sized second Phase particles or fibers, nanocrystals in a glassy Matrix, Phase separated regions, variations in short-range order by clustering) have been reported. We developed bulk metallic glasses and glass Matrix composites in martensitic Zr–Cu-base alloys. Large plasticity can be obtained from microstructure consisting of either a glassy structure, or for alloys with martensitic second Phase embedded in a glassy Matrix. This type of glasses and glass–Matrix composites are able to achieve high strength together with pronounced work-hardening. We explore the possibilities to synthesize such in situ composite microstructures based on shape memory alloys (“M-Glasses”) through metal mold casting.

Stefan Zaefferer - One of the best experts on this subject based on the ideXlab platform.

  • Phase diagram mapping of the fe3al cr mo c pseudo quaternary system at 800 c using a new diffusion multiple technique
    Journal of Phase Equilibria and Diffusion, 2008
    Co-Authors: Satoru Kobayashi, Stefan Zaefferer
    Abstract:

    A new diffusion-multiple technique was used for mapping the Phase diagram in the pseudo-quaternary Fe3Al-Cr-Mo-C system at 800 °C. The following five carbide Phases were formed in an Fe3Al Matrix Phase (B2) with composition gradients of Cr, Mo, and C in the diffusion-multiple samples: κ-Fe3AlC, M5C, M6C, Cr7C3, and M2C (M: Mo, Cr, Al, and Fe). It was assumed that B2 Phase is in equilibrium with κ, M5C, M6C, and Cr7C3 but not with M2C Phase at 800 °C. Complex Phase equilibria among those Phases were efficiently mapped by the diffusion-multiple technique. The results from the technique were consistent with those obtained from the conventional bulk alloy method.

  • determination of Phase equilibria in the fe3al cr mo c semi quaternary system using a new diffusion multiple technique
    Journal of Alloys and Compounds, 2008
    Co-Authors: Satoru Kobayashi, Stefan Zaefferer
    Abstract:

    A new diffusion-multiple (DM) technique was proposed to allow us mapping of quaternary Phase diagrams. This technique utilizes a combination of DM technique to introduce two-dimensional composition gradients in a Matrix Phase and a conventional annealing heat treatment to have precipitation reactions in the Matrix. Phase equilibria at 800 °C in the semi-quaternary Fe 3 Al-Cr-Mo-C system were determined with an assist from this technique. The following five carbide Phases were precipitated in the Fe 3 Al Matrix Phase (B2) with composition gradients ofCr, Mo and C: K-Fe 3 AlC, M 6 C H , M 6 C L , Cr 7 C 3 and M 2 C (M: Mo, Cr and Fe, the two M 6 C Phases are distinguished by their C and Cr contents.). It was found from our DM technique that the four-Phase equilibrium of M 6 C H + M 6 C L + Cr 7 C 3 +B2 exists. Microstructure analysis of several bulk alloys as well as DM samples revealed that the three-Phase equilibrium of M 6 C L + K + B2 in the Fe 3 Al-Mo-C system changes to that of M 6 C L + Cr 7 C 3 + B2 with increasing Cr content through the following three four-Phase equilibria: (1) M 6 C H + M 6 C L + K + B2, (2) M 6 C u + Cr 7 C 3 + K + B2, (3) M 6 C H + M 6 C L + Cr 7 C 3 + B2. The M 2 C Phase is thought to be not in equilibrium with the Fe 3 Al Matrix Phase at 800 °C.

Woon Hyung Baek - One of the best experts on this subject based on the ideXlab platform.

  • microstructure and mechanical properties of mechanically alloyed and solid state sintered tungsten heavy alloys
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2000
    Co-Authors: Soon Hyung Hong, Woon Hyung Baek
    Abstract:

    The mechanical properties of solid-state sintered 93W‐5.6Ni‐1.4Fe tungsten heavy alloys fabricated by mechanical alloying were investigated. Blended W, Ni and Fe powders were mechanically alloyed in a tumbler ball mill at a milling speed of 75 rpm employing a ball-to-powder ratio of 20:1 and a ball filling ratio of 15%. A nanocrystalline size of 16 nm and fine lamellar spacings of 0.2 mm were obtained in mechanically alloyed powders at a steady state milling stage. Mechanically alloyed powders were consolidated into green compacts and solid-state sintered at 1300°C fo r1hi n ahydrogen atmosphere. The alloys sintered from mechanically alloyed powders showed fine tungsten particles (about 3 mm in diameter) and a relative density above 99%. The volume fraction of the Matrix Phase was 11% and the tungsten:tungsten contiguity was determined to be 0.74. The alloys exhibited high yield strengths (about 1100 MPa) due to their fine microstructures, but exhibited reduced elongation and impact energy due to a large area fraction of tungsten:tungsten boundaries and the low volume fraction of Matrix Phase. © 2000 Elsevier Science S.A. All rights reserved.

Rehan Ahmed - One of the best experts on this subject based on the ideXlab platform.

  • single asperity nanoscratch behaviour of hiped and cast stellite 6 alloys
    Wear, 2014
    Co-Authors: Rehan Ahmed, Nadimul Haque Faisal, A Ashraf, M Elameen, A M Elsherik, Youssef O Elakwah, Matheus F A Goosen
    Abstract:

    Abstract The aim of this study was to investigate the nanoscale sliding wear behaviour of re-HIPed (Hot Isostatically Pressed) and cast cobalt-based Stellite 6 alloys. A nanoindentation system equipped with a wear testing module was used to simulate single asperity deformation behaviour using a sphero-conical indenter. The test load was either increased linearly over the sliding distance or ramped upto full load at the initial stage of the test. Post-test evaluations included X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and atomic force microscopy (AFM) measurements. An elastic–plastic finite element model (FEM) was used to compare the displaced volume with the experimental data. Results are discussed in terms of the structure–property relationships and indicated that the nanoscale wear was dominated by the composition and nanomechanical properties of the metal Matrix, and also the shape and size of carbides. Wear predominantly occurred due to plastic deformation of the metal Matrix Phase. Relatively higher scratch resistance and hardness of the metal Matrix Phase, coupled with the microstructural homogeneity of re-HIPed alloy led to its lower wear volume loss, in comparison to the cast counterpart. The FEM predictions were in agreement with the experimental results, and the error between the two ranged from 0% to 25% under the loading conditions considered in this investigation.

Ali Kalkanli - One of the best experts on this subject based on the ideXlab platform.

  • processing and microstructural characterization of liquid Phase sintered tungsten nickel cobalt heavy alloys
    International Journal of Refractory Metals & Hard Materials, 2015
    Co-Authors: Onur Dincer, Kaan M Pehlivanoglu, Kaan N Caliskan, Ishak Karakaya, Ali Kalkanli
    Abstract:

    Abstract In this study, the effects of composition and sintering temperature on the microstructural characteristics of liquid Phase sintered 90W–Ni–Co alloys were investigated. 90W–Ni–Co alloys having Ni/Co ratios of 3/1, 4/1 and 6/1 were examined. It was found that the alloys studied have reached almost to full density when sintered at and above 1475 °C. The microstructures of the alloys were typical of liquid Phase sintered alloys, which consisted of rounded, nearly pure W grains embedded in a ternary Ni–Co–W binder Matrix Phase. The binder Matrix Phase in these alloys was observed to dissolve up to 42 wt.% W. The relative amount of the binder Matrix Phase and the average size of the W grains were found to increase with increasing sintering temperature. The activation energies for grain coarsening are determined for the investigated alloys by assuming that the coarsening process is mainly governed by Ostwald ripening mechanisms in the liquid state. The calculated activation energies, which were within 113–162 kJ/mol range, were found to be in rather close agreement to the literature data given for W–Ni–Fe alloys. This indicates that grain coarsening in W–Ni–Co and W–Ni–Fe alloys most probably takes place through similar diffusional processes.