The nature of c-component dislocations in samples of a polycrystalline Ti3 Al-based alloy deformed at room temperature and at 300°C

Abstract

Polycrystalline specimens of a Ti-25A1-4Nb (at.%) alloy having the DO₁₉ structure have been deformed in compression at both room temperature and 300°C to true strains of about 1% and 3%. The nature of the c-component dislocations in samples compressed to these two levels of strain is different; in the case of the lower strain, the dislocations have b = [0001], whereas in the more highly deformed samples the predominant dislocations have b = 1/6 (that is c + a/2). The dislocations with b = c have been shown to lie on {10 0}, {11 0} and {3 10}; however, it has been assumed that these dislocations are sessile. Those dislocations with b = 1/6 are present in the form of widely separated bands of pairs of loosely coupled superpartials gliding on { 111} planes. In many of the images of these dislocations, there are fringes associated with the slip planes. These have been interpreted on the basis of antiphase boundaries produced by glide of jogged superpartial dislocation pairs. Also, there is extensive dislocation debris present in the microstructure; this appears to correspond to dislocation dipoles formed by the intersection of dislocations with b = a and (c + a/2).