Nanoscale twinning in thin films
Twinning can be obtained by different processing techniques, such as annealing, plastic deformation and growth process. According to their processing history, twins can be named as annealing twins, deformation twins and growth twins. It is known that twinning is a particularly important deformation mechanism in crystals with only a limited
Bright field TEM of 330 SS films with an average columnar
grain size of around 30 nm, showing high density twinning
within the columnar grains.
number of slip systems. However, research on the influence of twin interface on mechanical, electrical and other properties is still at a very early stage. One of the reasons is that it is difficult to predict or control the microstructure (e.g. coherent vs. incoherent twin interface) or geometry (twin spacing or the twin width) of twins. Twinning with twin spacing of less than 100 nm is rarely observed. Even after extremely high strain rate deformation, such as shock loading of a typical stainless steel, the twin spacing is over 100 nm.
Among the three types of twins, we are especially interested in growth twins. As the microstructure and geometry of growth twins could be precisely controlled by tailoring the growth process (such as physical vapor deposition). Studies on growth twins will provide important foundation for engineering design twin interface at small length scale with desired properties. [Read more...]
