Marx, V.M.; Kirchlechner, Ch.; Breitbach, B.; Cordill, M.J.; Többens, DM.; Waitz, T.; Dehm, G.: Strain-induced phase transformation of a thin Co film on flexible substrates. Acta Materialia 121 (2016), p. 227-233
10.1016/j.actamat.2016.09.015

Abstract:
The strain-induced FCC to HCP phase transformation of a two phase Co film on polyimide was investigated by performing a tensile test in an X-ray diffractometer. During straining of the 2 μm thick film, the intensity of the (002)FCC peak continuously decreases at engineering strains between 2 and 8% and remains constant at higher strains. Complementary in situ tensile tests under an optical light microscope showed crack formation at 6.7% and crack saturation at around 10% engineering strain. The strain-induced phase transformation starts before the first cracks form leading to a maximum lattice strain of approximately 0.9%, which converts to a film stress of approximately 1270 ± 150 MPa. It could be revealed that a strain-induced phase transformation can enhance the ductility and therefore delay the crack onset of a thin cobalt film.