Multiple cracking of tantalum by hydrogenation

The fracture behavior and microstructure changes of pure Ta by hydrogenation have been investigated to elucidate the fundamentals for hydrogen pulverization, which can be used for producing fine Ta powder with high purity and low cost. Concentric cracks are introduced in a recrystallized Ta plate, with a grain size of about 100 μm, when the Ta plate is annealed at 1473 K and cooled in a hydrogen atmosphere. On the other hand, no crack is observed when the Ta plate is annealed at 1473 K in a hydrogen atmosphere and cooled in an argon atmosphere. It is suggested that the surface activation caused by annealing in a hydrogen atmosphere at 1473 K facilitates hydrogen absorption at lower temperatures, and the volume expansion and the hydride formation generated by hydrogen absorption lead to multiple cracking. The multiple cracking in the Ta plate occurs in the following sequence: (1) hydrogen absorption, (2) strain generation by volume expansion and hydride formation, and (3) crack nucleation and propagation.