Strengthening of lamellar TiAl alloys by precipitation bands of βo particles

Certain β forming atoms, such as W, segregate into α2 plates and form precipitation bands of β0 particles during dissolution of α2 plates at high temperature. Creep properties of TiAl alloys containing β0 precipitates are studied, and their microstructural and alloy design is discussed on the basis of microstructural changes occurring in the alloys. Precipitation bands of β0 particles reduce minimum creep rate and extend time to 1% strain and rupture life of the alloys. Creep resistance of the alloys is as good as a hard-oriented polysynthetically twinned crystal of a TiAl alloy. α2 plates thicker than a critical size is necessary to form the precipitation bands and utilize the benefits of precipitation strengthening. Microstructural degradations, such as agglomeration and dissolution of β0 particles and dynamic recrystallization play significant roles in long-term creep. Retardation of the particle degradations is necessary to make efficient use of the strengthening by β0 precipitates.