Influence of Voids on the Accuracy of Measurement of Vacancy Concentration in NiAl and CoAl Intermetallic Compounds

概要

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The vacancy concentrations $c_{\text{v}}$ in the B2-type alloys of Ni1-xAlx ($0.45\leq x\leq 0.54$) and Co1-xAlx ($0.46\leq x\leq 0.52$) were determined by the measurements of lattice constant with X-ray diffraction and bulk density $\rho_{\text{A}}$ using the Archimedes method. The measurements were performed at room temperature for various sizes of powder samples. The obtained density of $\rho_{\text{A}}$ increased with decreasing powder size, and the resultant vacancy concentration decreased. The size dependence of $\rho_{\text{A}}$ and a scanning electron microscopic observation indicated that the increase in $\rho_{\text{A}}$ was due to the presence of voids in the powder samples. The reliable values of $c_{\text{v}}$ were estimated using a model that reduced the influence of voids. The effective formation energies of vacancy and antistructure atom were also estimated from the composition dependence of $c_{\text{v}}$. The results of the estimation showed that the Al antistructure is the ground state of the defect structure at 0 K.
Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physicsの論文
2004-05-15