Grain Size Effect on Mechanical Properties Under Biaxial Stretching in Pure Tantalum

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This paper reports the mechanical properties and formability under biaxial stretching in pure tantalum as a function of average grain size. The grain size of pure tantalum was adjusted from submicron to tens of micron using the high-pressure torsion process and subsequent annealing. The stretch formability was evaluated using a miniaturized Erichsen tester. Under uniaxial tension, the mechanical properties of pure tantalum followed the typical strength-ductility trade-off behavior according to the average grain size. Nevertheless, the stretch formability became rather significantly inferior in the coarse-grain tantalum, which was primarily attributed to the poor resistance to strain localization and limited work hardening capacity. This deterioration was supposed to be due to the intensified strain localization with increasing the average grain size, based on the in-grain deformation heterogeneity within individual grains and the surface roughening after the Erichsen test. Consequently, this study suggests that the excellent stretch formability and work hardening capacity under biaxial loading can be achieved at a certain range of the average grain size (8.25–19.3 μm in this work).