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 Sigma3(n) (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 Sigma3 twin boundaries (as distinct from Sigma3 grain boundaries) are discounted, the Sigma3(n) distribution for both specimens had a peak at Sigma9, because Sigma3 + Sigma9 --> Sigma3 occurs more frequently than Sigma3 + Sigma9 --> Sigma27. The distributions and reactions between various Sigma3(n) values are described and discussed in detail. A novel trace analysis procedure is used to extract information from Sigma3 boundaries to decide whether or not they are annealing twins, and so provide a convenient means to assess proportions of twin and non-twin Sigma3s. The data show unambiguously that a significant proportion of Sigma3s are not on {111}, and these boundaries have on average higher angular deviations from the exact Sigma3 reference misorientation than do other Sigma3s. A population of Sigma3s which were vicinal to annealing twins were also recorded. These data support the contention that profuse annealing twinning produces concurrently many not-twin Sigma3s, which are pivotal in grain boundary engineering. (C) 2005 Springer Science + Business Media, Inc.