PHASE-TRANSFORMATIONS IN THE TI-H AND ZR-H SYSTEMS AT HIGH AND ATMOSPHERIC PRESSURES

The T - P diagrams of Ti - H and Ti - D systems were studied at pressu res of 25 to 65 kbar, and a marked isotope effect was observed for the minimum pressure when the high-pressure phase appeared. The occurrenc e of another high-pressure phase is concluded from splitting of one of the transformation lines at P > 40 (50) kbar. Transformations of the X-phase quenched under pressure (chi --> kappa + Ti --> gamma + Ti in TiH(D) - 0.75) were studied at P = 1 atm by calorimetric and neutron s cattering techniques. A double-peaked exothermal effect evidenced meta stability both of chi- and intermediate kappa-phases. The hydrogen in the intermediate kappa-phase was partially ordered in tetrahedral inte rstices on alternate {110} planes. Complete H ordering resulted in sto ichiometric gamma-TiH and precipitation of disperse Ti. Parameters of the transformations exhibited a considerable isotope effect. The gamma to alpha + delta transformation in the Zr - H system is reversible, t herefore, gamma-ZrH is a stable phase below the transformation tempera ture. A phase transformation was found in deficient dihydrides, ZrH1.5 9 and ZrD1.69, under pressure.