Role of lamellar plates in creep of TiAl alloy with fully lamellar structure

Abstract

The role of lamellar plates in near γ Ti–48 at.% Al alloy with fully transformed lamellar structure was investigated by studying the difference in creep rate–time curve between Ti–48 at.% Al alloy and the γ single phase Ti–50 at.% Al alloy. Creep tests were conducted at 1123 K under a low stress of 68.6 MPa. The superiority of FL specimen is derived not from decreasing the creep rate, but from retarding the onset of accelerating creep. The absence of dynamic recrystallization along grain boundaries is interpreted as causing retardation of accelerating creep. The α 2 lamellar plates have a more drastic effect on suppressing dynamic recrystallization than the γ lamellar plates. Dynamic recrystallization would be fully suppressed in a Ti–Al PST crystal, because of the absence of grain boundaries. By conducting the creep tests of PST crystals with different lamellar orientations to stress axis, φ, φ dependence of creep rate was investigated. In the specimens with φ from 30 to 70°, creep rate is larger than that in polycrystalline FL specimen. For the specimen with φ less than 30° and larger than 80°, the creep rate becomes smaller than that of the FL specimen, and in the case of the specimens with φ near 0 or 90° a marked decrease in creep rate is confirmed. The correlation between interlamellar spacing and creep rate is investigated using FL specimen with four different interlamellar spacing. Decreasing the interlamellar spacing gives a short transient stage and a short accelerating stage.