Intermediate temperature creep properties of gamma TiAl

Compressive creep tests of single phase gamma Ti47Al51Mn2 have been conducted at stresses from 280 to 400 MPa in a temperature range of 500-600 degrees C. The creep curves exhibited a primary region in which the creep rate decreased rapidly, a secondary region corresponding to a minimum creep rate, and an extended tertiary region in which the creep rate increased steadily with time. Unlike yielding, the creep behavior of this alloy was found to be normal; creep strength decreased with increasing temperature. Temperature change experiments and TEM observations have clearly elucidated the fact that a microstructural steady-state is not attained in the creep of this alloy. Instead, the overall creep performance is dominated by the tertiary creep that results from internal changes in the deformation microstructure. Although several dislocation and twinning mechanisms have been associated with the creep of TiAl, the multiplication and increased mobility of ordinary dislocations was found to play a dominant role in determining the creep behavior of this alloy. (C) 1997 Acta Metallurgica Inc.