ANALYSIS OF THERMAL AND ATHERMAL DEFORMATION MECHANISMS DURING CREEP OF GAMMA-TIAL ALLOYS

The creep deformation of a near-gamma titanium aluminide alloy with eq uiaxed and lamellar structures has been studied to understand its beha viour as a function of microstructural evolution during the early stag es of creep. The lamellar alloy exhibits more pronounced hardening dur ing the primary stage of creep leading to a much better creep resistan ce and a minimum creep rate two orders of magnitude lower than that of the equiaxed alloy. Transmission electron microscopy observations hav e confirmed that the active deformation mechanisms are the same for bo th microstructural states, namely extensive slip of single 1/2[110] di slocations and mechanical twinning. Using the values of apparent activ ation energies and activation volumes measured for both microstructura l states, it has been possible to describe the better creep resistance of the lamellar alloy to the presence of a higher density of interfac es at which dislocations remain immobile. (C) 1997 Elsevier Science S. A.