Plastic deformation mechanism of TA1 pure titanium plate using SEM-EBSD in-situ tensile testing

Abstract

As the core component of proton exchange membrane fuel cell (PEMFC), pure titanium bipolar plate has been faced with cracking and thinning problems in the forming process. It is considered that the stamping and tensile deformation of the bipolar plate have similar stress states. In this paper, the plastic deformation mechanism of TA1 pure titanium plate is analyzed from the aspects of twin, texture evolution and dislocation slip by in-situ tensile combined with SEM/EBSD. During tensile deformation, a large number of dislocation slips occur inside α grain, and obvious slip traces are produced on the surface of the sample. Within grains with different crystallographic orientations, the degree and direction of the trace are different, which leads to the increased disharmony between grains. Especially in the triple junction of grain boundary, soft/hard orientation grain junction and other deformation disharmony locations are easy to crack. The tensile deformation causes obvious changes in the texture, and the initial strong bimodal texture becomes weak bimodal texture. This phenomenon is explained by intragranular misorientation, crystal rotation and twins. The main mechanism of tensile deformation of titanium plate is slip and twinning. A large number of {11–22}<11-2-3> compression twins are formed due to most c-axis bearing compressive stress. The types of initiating slip systems are different in different stages. The cylindrical slip system is preferentially activated and occupies a dominant position before yielding, which is conducive to the plastic forming of the plate. After yielding, the start-up ratio of the pyramidal slip system is increased due to the deflection of the observed surface of sample during tensile process, which improves the deformation resistance of the thin plate.