Precipitation Mechanisms of Ordered Phases in Ti-and Ni-base Alloys

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The mechanisms for decomposition processes of alpha-and beta-phases in Ti-Al base intermetallics have been analyzed in terms of crystallography.1.the beta-phase stabilizes with increasing Zr and decomposes into Widmanstatten structure of alpha_2-phase by the Shear-Assisted Diffusional Transformation mechanism (SADT).2.In 30-50at.%Al, (alpha_2+gamma) lamellar structure uncleates at the grainboundary gamma-allotriomorph by the SADT with the Blackburn orientation relationship.3.Maasive structure, which consists of both alpha_2 and gamma, forms with the orientation relationships, {111}_<gamma>//{1011}_<alpha> and <110>_<gamma>//<1210>_<alpha>, in * 45at.%Al.In Ni-base superalloy, the preprecipitation stages of ordered phases, which control the age-hardening, have been analyzed in terms of the interaction of solute atoms with lattice defects.1.Quenched-in excess vacancies alter the nature of dislocations and enhance the trapping of solute atoms at the dislocations.2.The trapping of solute atoms at the dislocations delays the ordered-phase precipitation as well as age-hardening, remarkably.