THE MOVEMENT OF SINGLE BETA(1)-]BETA(1)' INTERFACES IN CU-ZN-A1 AS STUDIED BY A NEW TECHNIQUE OF INTERNAL-FRICTION MEASUREMENT

A new technique of internal friction (IF) measurement has been develop ed in order to study the beta1/beta1' interface motion in Cu-Zn-Al sin gle crystals. In contrast to the conventional IF techniques, which onl y allow for the study of thermally-induced polyvariant martensitic tra nsformations, the new technique employs a special torsion pendulum in which stress-induced single variant transformations can be studied. Th e specimen geometry (''window'' specimen) was modified such that the o scillating measuring stress (sigma(m)) creates a net shear stress in t he habit plane, and induces a ''global'' beta1/beta1' interface displa cement. By using this new technique it could be demonstrated that the majority of energy dissipation occurs by shear deformation in the habi t planes. A new IF model is proposed which considers the microscopic s tress hysteresis (DELTAtau(m)) that is associated with the motion of b eta1/beta1' interfaces. With this model, quantitative values for DELTA tau(m) can be derived from the measured IF values, and it was shown th at the microscopic stress hysteresis is small for the beta1/beta1' int erface motion in a precipitate-free matrix (DELTAtau(m)I = 0.2 MPa), b ut increases when gamma precipitates oppose the interface motion (DELT Atau(m)II = 0.6 MPa).