Distinct orientation dependence of plasticity initiation and subsequent deformation in nanoindented tungsten

As refractory metals are increasingly subjected to extreme service conditions, a comprehensive understanding of their fundamental deformation mechanisms has become indispensable, particularly considering the persistent discrepancies between predicted and experimentally observed behavior under complex stress fields. Therefore, nanoindentation on the principal crystallographic planes of pure tungsten single-crystals was performed and revealed a strong influence of crystal orientation on indent appearance, hardness and incipient plasticity. For the (100) surface we observe a confined plastic zone with pronounced pile-up and highest hardness of 5.18 ± 0.07 GPa among the three orientations. Unusually long streaks of dislocations form on the surface of (110)-oriented samples demonstrating tungsten's non-Schmid behavior. The (111) surface exhibits hitherto unreported appearance of slip and highest pop-in loads.