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Combined HRTEM and EFTEM Study of Precipitates in Tungsten and Chromium-Containing TiB2

  • W. Mader (a1), B. Freitag (a2), K. Kelm (a2), R. Telle (a3) and C. Schmalzried (a3)...

Abstract

The structure and chemical composition of two types of precipitates in the system TiB2-WB2-CrB2 were studied by means of high-resolution TEM and energy filtering TEM. Type I particles (W2B5 structure) are precipitated at the basal plane of the hexagonal matrix whereas type II precipitates are thin platelets lying parallel to the {1100} prism planes. Lattice imaging yields displacements of the metal positions with respect to the matrix. Information on the chemical composition at high lateral resolution is obtained from elemental maps of all chemical constituents using electron spectroscopic imaging (ESI). The type II precipitates show a decrease in the B and Ti concentration, whereas the tungsten concentration increases and the Cr is homogeneously distributed. The HRTEM results combined with the results of the elemental maps allow to develop a structural model based on the intergrowth of the β-WB structure in the TiB2-rich matrix. The two deficient boron layers in W0.5Ti0.5B with a spacing of 0.38 nm can be used to examine the resolution limit of ESI.

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