The influence of annealing twinning on microstructure evolution.

This paper reports an experimental investigation on the effect of multiple twinning on the interface population in two low stacking-fault alloys. This is an important topic for grain boundary engineering because annealing twinning is the indirect cause of improved intergranular corrosion resistance in this class of materials. Proportions of S 3ⁿ (n= 1-5) boundaries were analysed in both a brass specimen and a superalloy specimen where the boundaries had been processed so as to be very mobile and less mobile respectively. When S 3 twin boundaries (as distinct from S 3 grain boundaries) are discounted, the S 3ⁿ distribution for both specimens had a peak at S 9, because S 3 + S 9 ? S 3 occurs more frequently than S 3+S 9 ? S 27. The distributions and reactions between various S 3ⁿ values are described and discussed in detail. A novel trace analysis procedure is used to extract information from S 3 boundaries to decide whether or not they are annealing twins, and so provide a convenient means to assess proportions of twin and non-twin S 3s. The data show unambiguously that a significant proportion of S 3s are not on 111, and these boundaries have on average higher angular deviations from the exact S 3 reference misorientation than do other S 3s. A population of S 3s which were vicinal to annealing twins were also recorded. These data support the contention that profuse annealing twinning produces concurrently many not-twin S 3s, which are pivotal in grain boundary engineering. [ABSTRACT FROM AUTHOR]