Bismuth is known to segregate to grain boundaries in copper resulting in embrittlement and intergranular failure at low stress levels. This segregation has been studied primarily by Auger Electron Spectroscopy (AES). The applicability of scanning transmission electron microscopy (STEM)and Energy Dispersive Spectroscopy (EDS) to the study of equilibrium grain boundary segregation has already been demonstrated and the aim of this study is to determine the degree of segregation as a function of time and temperature. The major advantage of STEM over AES is that STEM does not require fracturing of the specimen, so the boundaries to be studied are left undisturbed. Thus, this technique is also applicable to systems which do not exhibit intergranular fracture.Cu-Bi specimens were prepared by evaporating Bi onto both sides of 3mm Cu discs, which were then heated for 1 week at 400°C to allow the Bi to diffuse into the Cu. The samples were then aged at 450, 550, 600, 650, and 700°C for 3 days and 12 days, ion-thinned and then examined in a Philips EM 400T TEM/STEM with an EDAX detector and EDAX 9100 analyzer. If necessary, the specimens were tilted such that the boundaries were parallel to the electron beam.
Measuring grain boundary segregation: tomographic atom probe field ion microscopy (APFIM) vs. analytical scanning transmission electron microscopy (STEM)
