Microstructure in Ti–48at.%Al PST crystal subjected to creep deformation

Tensile creep tests of the Ti–48at.%Al PST crystals with different lamellar orientation angles with respect to the stress axis φ were conducted at 1148 K and 68.6 MPa and the φ dependence of creep rate was investigated. The creep rate of the PST crystal strongly depends on φ. The minimum creep rate of the PST crystal with φ=63° is three orders of magnitude larger than that of the PST crystal with φ=3°, and the rupture life of the PST crystal with φ=63° is one-tenth of that of the PST crystal with φ=3°. The marked differences in creep rate and rupture life between the PST crystal with φ=63° and that with φ=3° would be ascribed to the role of α2 plate to the operative slip systems. To confirm the above supposition, creep interruption tests in the wide strain range were conducted for the PST crystal with φ=63°. The microstructure of the creep interrupted specimens gives the evidence to understand the role of α2 plate to creep property, that is, the evolution of subgrain occurs just after collapsing of the α2 plates, and the collapse of the α2 plates directly coincides with the onset of accelerating creep.