Martensitic transformation in Ag-Cd and Cu-Zn alloys studied by nuclear magnetic resonance.

Abstract

$^{113}\mathrm{Cd}$, $^{109}\mathrm{Ag}$, and $^{63}\mathrm{Cu}$ nuclear-magnetic-resonance line-shape and Knight-shift measurements are reported for ${\mathrm{Ag}}_{53.5}$${\mathrm{Cd}}_{46.5}$ and ${\mathrm{Cu}}_{61}$${\mathrm{Zn}}_{39}$ over a temperature interval covering the martensitic phase transformation (MPT) displayed by these alloys. The changes observed in the line shape and width are explained in terms of the changes in atomic coordination and crystal symmetry occurring at the MPT. A small but non-negligible temperature dependence of the Knight shift is observed in the austenitic phase with small discontinuous changes at the transformation for all the nuclei investigated. The difference of resonance frequency of $^{113}\mathrm{Cd}$ in the two phases has been utilized to obtain the curve of the percentage of martensite in the Ag-Cd alloy as a function of temperature during the thermoelastic transformation. It is shown that our growth curve reveals details which cannot be seen by dynamical methods such as differential scanning calorimetry.