Slip mode analysis in BCC tantalum with HRDIC

Slip in BCC metals is reported to include pencil glide on maximum shear stress planes (MSSPs) as well as slip on various standard crystallographic slip systems. High-resolution digital image correlation (HRDIC) often enables unambiguous grain-scale slip analysis and was used to characterize the slip modes in large-grained BCC tantalum tensile specimens in the current work. Slip of {110}, {112} and MSSP types was observed based on the slip trace analysis. The critical resolved shear stress (CRSS) for {112} slip is approximately 9.5 % higher than {110} slip while the CRSS for pencil glide is approximately 7.3 % higher than for {110} slip. Activation of unexpected slip systems near grain boundaries was found to be dependent on the local stress states. HRDIC reveals the size of the grain boundary zone (GBZ), with strain decreasing toward the grain centers, and the width of the GBZ is determined to be approximately 140 μm in the region of GBs that exhibited clear strain gradients, for grains of average diameter 10 mm, and with little slip transmission across the GB observed.