Dilute Al and V NMR in alpha -Ti.

Abstract

We report a nuclear-magnetic-resonance investigation of four titanium alloys: Ti--1 at. % V, Ti--2 at. % V, Ti--1 at. % Al, and Ti--2 at. % Al. Interpretation of the experimental $^{51}\mathrm{V}$ and $^{27}\mathrm{Al}$ absorption curves was accomplished largely by comparison with computer-simulated curves. Since the latter include the effects of nuclear-quadrupole and anisotropic Knight-shift interactions, dipolar broadening, and inhomogeneous Knight shift for the V and Al solute nuclei, the comparison yields experimental values for the electric-field gradient, axially symmetric anistropic Knight shift, and isotropic Knight shift, from which we attempt to deduce the local charge distribution at the V or Al atoms in the hcp \ensuremath{\alpha}-Ti matrix. We find that the localized states on an Al impurity exhibit very little of the character of the host Ti atomic structure. There is no orbital contribution to the Knight shift and the s conduction-electron density at Al sites is small. On the other hand, when vanadium is present as a dilute solute in the Ti lattice, only minor changes in its Knight shift are found. There is a large orbital-shift contribution, and the V nuclear absorption exhibits much the same character as in pure metallic V; there is, however, clear evidence of the V charge distribution assuming the hexagonal symmetry of the Ti lattice. The measured temperature dependences of the anisotropic Knight shift and electric-field-gradient values at V solute sites in Ti are also discussed. On partitioning the field gradient we find that the contribution from local non-s electrons is about two to five times larger in magnitude than the Ti-lattice ion value, a strong indication that the electronic structure near V (but not Al) resembles that of the matrix Ti.