Abstract:Binary TiMn₂ alloys with various compositions were arc melted in an Ar atmosphere. These alloys consist of TiMn₂ and a small amount of TiMn depending on alloy composition. Annealed Ti-59.4%Mn exhibits the greatest capacity for hydrogen absorption and the smallest degradation of capacity during repeated hydrogen absorption and desorption. No apparent macro- and microstructural changes are observed in Ti-59.4%Mn by repeated hydrogenation of 30 cycles. At Mn content higher than 59.4%Mn, the formation of nano-sized Ti-hydride and the lattice expansion due to retained interstitial hydrogen were confirmed in repeatedly hydrogenated alloys. Pulverized powders were refined in all the alloys with in creasing the number of repeated hydrogenation cycles. Many onion-like cracks are introduced in annealed pure Ta with 100μm equi-axed grains by holding at 1473K followed by furnace cooling to room temperature in a hydrogen atmosphere, but no crack is observed after holding at 1473K in a hydrogen atmosphere followed by furnace cooling in an Ar atmosphere. It is concluded that the surface activation is attained in a hydrogen atmosphere at 1473K and multiple cracking occurs by absorbing a large amount of hydrogen at lower temperature. Volume expansion and dislocations generated b y hydrogenation and hydride formation are responsible for multiple cracking. Hydrogen-induced multiple cracking in Ta occurs in the following sequence: hydrogen absorption, lattice expansion, hydride formation, and crack nucleation and propagation. Powder fabrication of Ta by hydrogenation is discussed in comparison with the hydrogen pulverization of intermetallic alloys.

Key words: macrostructure; microstructure; hydrogen absorbing alloy