Surface phase transformation induced by the dezincification of a beta Cu-Zn alloy on highly deformed systems

When Cu-Zn alloys are annealed under dynamical vacuum the Zn component evaporates. The process is called dezincification. This paper presents the results of the dezincification of highly mechanically deformed surfaces of samples initially in the beta (bcc) phase by a combination of in situ optical microscopy observations together with TEM measurements. It is shown that grinding lines remaining from the sample preparation process act as nucleation centers for the alpha (fcc) phase. Under this surface preparation conditions the new fcc phase nucleates with a different geometry than the one reported in previous papers in which surfaces were finished by electropolishing. In the present case, we observe individual fcc precipitates with a well defined geometry. The typical size of precipitates is in the micron range, and depends on the dezincification parameters: final temperature, dezincification time and prior surface preparation. TEM observations show that the fcc precipitates contain a large density of defects, mainly dislocations and twin boundaries.