The influence of temperature and alloying additions on the mechanisms of plastic deformation of Ti3Al

Abstract

Samples of polycrystalline Ti₃Al and Ti₃Al containing 4 at.°Nb in solution (substituted for Ti) have been deformed at room temperature and at 650°C and examined subsequently by transmission electron microscopy in order to determine the influence of temperature and alloy content on the relative activity of the various slip systems. It has been shown that at room temperature in Ti₃Al the deformation mechanisms involve glide of coupled pairs of dislocations with b=1/6 on {1010} and, to a rather limited degree, glide of pairs of dislocations with b=1/6 on {112 1}, with the extent of the particular slip system which operates varying between grains of different orientations. At 650°C, glide of these two types of slip system occurs, but the morphology of slip of the dislocations with b =1/6 changes at the elevated temperature. Furthermore, evidence for the climb of dislocations has been obtained, which may produce strain at elevated temperatures. Only limited activity of the (0001) slip systems in stoichiometric Ti₃Al deformed at either of the temperatures has been observed, even when they are highly stressed. In contrast, samples containing 4 at.°Nb exhibit significant slip of {1010}, (0001) and {112 1}, in addition to some slip on {1011}. The same slip systems are observed in samples deformed at 650°C. These observations are interpreted on the basis of the factors which control the mobility of dislocations in the various slip systems, the most significant of which appears to be the influence of covalency, and also in terms of the role of dislocation climb. The influence of these factors on the ductility of this intermetal-lic compound is discussed.