Investigation of microplastic deformation mechanisms in TA2 metallic bipolar plates using a crystal plasticity model coupling slip and twinning

Metallic bipolar plates (MBPS) serve as the core components of hydrogen fuel cells, tasked with transporting reactant gases, conducting electrical current, providing sealing structures, and other functions. Stamping is the primary method for fabricating micro channels in MBPS. However, severe thinning and even fracture of bipolar plates can occur during micro-stamping. Aiming to investigate the deformation mechanisms of MBPS in the process of microplastic forming,this work selected TA2 (a commercial purity titanium) plate with a thickness of 0.1 mm and initial α-phase textures to conduct room-temperature tensile and micro-stamping experiments. Numerical simulation analysis was carried out in the finite element framework based on the established full-field crystal plastic constitutive model coupling slip and twinning. Significant uneven distribution of stress and strain was observed in the plates during the plastic forming process. The results showed that the weakening of the hindering effect of grain boundaries on dislocation slip with increasing grain size was the main reason for the decrease in flow stress and tensile strength. The thinning behavior of the plate exhibits a distinct size effect, where an increase in grain size leads to a more pronounced manifestation of the plate thinning phenomenon. The anisotropy between grains increases the inhomogeneity of grain deformation in the surface layer, which leads to surface roughening after plate forming. Size effect and crystal anisotropy are all important factors affecting the quality of polar plate forming. The current work provides an experimentally and computationally based guide for achieving low-cost, high quality forming and fabrication of MBPS.