Abstract
Transmission electron microscope investigation has been performed concerning the effect of Cr-precipitation on the mechanical properties of B2-ordered NiAl containing 4 mol.% to 8 mol.% of Cr. By aging at temperatures around 973 K after solution annealing, fine spherical precipitates appeared homogeneously in the NiAl matrix and the alloys hardened appreciably. The selected area electron diffraction patterns have not revealed any additional extra-spots during aging, because the Cr-particles have a cube-cube orientation relationship and keep perfect coherency with the ordered matrix lattice. Dislocations bypass the particles during deformation. Although the dispersion of Cr-particles increases the yield strength of NiAl at intermediate temperature, the strength decreases appreciably at higher temperatures. Atom location by channeling enhanced microanalysis technique has been used to determine the site occupancy of Cr in NiAl.
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