Reducing the formation of FIB‐induced FCC layers on Cu‐Zn‐Al austenite

Abstract

The irradiation effects of thinning a sample of a Cu-Zn-Al shape memory alloy to electron transparency by a Ga(+) focused ion beam were investigated. This thinning method was compared with conventional electropolishing and Ar(+) ion milling. No implanted Ga was detected but surface FCC precipitation was found as a result of the focused ion beam sample preparation. Decreasing the irradiation dose by lowering the energy and current of the Ga(+) ions did not lead to a complete disappearance of the FCC structure. The latter could only be removed after gentle Ar(+) ion milling of the sample. It was further concluded that the precipitation of the FCC is independent of the crystallographic orientation of the surface.

FCC Surface Precipitation in Cu-Zn-Al after Low Angle GA<SUP>+</SUP> Ion Irradiation

“…9) These diffraction patterns and micro features were detected in all eight different samples irradiated with Ga þ ions with doses varying from 0.001 dpa to 15 dpa, the former being obtained in the cleaning processes with energies of 1 keV. 8) Also, in samples in which the inclination of the beam was larger than 5 or the crystallographic orientation of the sample was different from ½001 , only precipitation of FCC was observed, i.e. no 2H stacking was found.…”

“…Using eq. (1) the raise of temperature as a function of the dose 8) shows a linear behavior as shown in Fig. 3 and yielding the following parameters:…”

“…The dose could be varied in this equipment by changing the energy of the Ga þ ions and varying the current (a detailed calculation is given elsewhere 8) ). Also, two other samples with a calculated dose of 13 dpa were prepared.…”

“…Nevertheless, only an increase on the amount of precipitated FCC was detected in the sample where the crystallographic orientation of the irradiation sample was changed to ½102 . 8) Moreover, in Ref. 8) the formation of FCC after Ar þ ion milling for a sample prepared with a crystallographic orientation between ½102 and ½001 is reported.…”

“…8) Moreover, in Ref. 8) the formation of FCC after Ar þ ion milling for a sample prepared with a crystallographic orientation between ½102 and ½001 is reported. These tendencies show that the formation of the FCC after low dose irradiation is more related to the low irradiation angle as such than to the crystallographic orientation of the surface with respect to the incoming beam.…”