Development of Deformation Microtwins in Cu-Ni-Mn Continuously Cast Alloys

摘要

Microstructural studies involving transmission electron microscopy (TEM) have revealed that there is a transition of deformation mechanism from cross slip to twinning due to inhomogeneous distribution of stresses. A localized higher concentration of stresses due to a strong initial preferred orientation causes the onset of twinning. Micro diffraction revealed microtwins of less than 0.02 mu m in thickness, lying on {111} traces. All of the collected patterns around areas adjacent to the microtwinning are of the 110 type diffraction pattern with extra spots due to microtwinning. The misorientation between adjacent microtwinned regions is about 5 deg around the 110 pole. The existence of a high density of defects inside the microtwins is confirmed by the elongated spots in the selected area diffraction pattern. The transition from microband to microtwin formation is believed to be dependent on a localized concentration of stresses, while solute addition and stacking fault energy are believed to play a limited role.