The anomalous annealing hardening behaviors in commercial pure Tantalum foil

Abstract

Annealing softening phenomenon is usually observed in pure metals. However, in this study, the anomalous annealing hardening behavior is found in commercial pure Tantalum (Ta) foil. When the cold-rolled Ta foils are annealed at a temperature lower than 700 °C, both the yield strength and ductility gradually increase with the rise in annealing temperature, resulting in an anomalous "low-temperature annealing hardening" phenomenon. The yield strength of Ta foils annealed at 700 °C reaches the maximum value of about 750 MPa. This phenomenon in Ta foil is closely related with the shear bands and the pinning behavior between interstitial atoms and dislocations. When annealing temperature is higher than 700 °C, the yield strength decreases. When annealing temperature exceeds 900 °C, recrystallization occurs in Ta foil. Anomalous yield point phenomenon appears in the recrystallization foils during stretching, which is also related with the pinning of dislocations by interstitial atoms. As annealing temperature further increases, the volume fraction of surface grains gets larger. And {112}<111> slip systems are preferred over {110}<111> slip systems in the surface grains.