3-PHASE (BETA PLUS BETA' PLUS GAMMA') NI-AL-TI-(CR,FE) ALLOYS FOR HIGH-TEMPERATURE USE

The three-phase field incorporating the beta (NiAl), beta' (Ni2AlTi) and gamma' (Ni3Al) phases in the Ni-Al-Ti system was accurately determined. A number of alloys within that field, with or without boron, chromium or iron additions. were compression-tested for plastic deformability and for strength at room temperature and up to 800-degree-C. It was found that the presence of a substantial fraction of the relatively ductile gamma' phase in semicoherent epitaxy with beta and beta' conferred several per cent of compressive plasticity on these alloys. The strength of the best alloys remained impressively high up to about 650-degrees-C. Results of a TEM investigation of the behaviour of dislocations at room temperature in the beta and beta' phases of some of the three-phase alloys are outlined, and the process of "dislocation injection" from a more ductile into a less ductile phase is proposed as a general phenomenon.