The influence of purity on the mechanisms of plastic deformation of Ti3Al

Samples of rapidly solidified Ti-25 Al-0·4 Er(at.%) have been consolidated by hot isostatic pressing and deformed subsequently in compression at room temperature to ≈3% strain. In addition to dislocations with Burgers vectors, b, given by b=⅓ gliding on {10 1 0}, activity of these dislocations has also been observed on (0001). This result is in contrast to that expected of binary Ti 3 Al of nominal purity where glide of dislocations with b=⅓ on basal planes does not contribute significantly to the production of strain. This result has been attributed to the internal gettering of interstitial impurities resulting from the addition of Er. It is proposed that interstitial elements such as oxygen, carbon and nitrogen enhance the anisotropy of the charge distribution about Ti atoms, and so the consequence of removing these elements by gettering is to reduce the degree of directionality of bonding between the Ti atoms, and therefore the large Peierls stress associated with glide of both screw and edge segments of (0001). It is noted that it is not possible to resolve the expected superpartials of dislocations with b=⅓ lying on (0001), which places an upper limit of ≈2nm on their separation, which is to be compared with a separation of ≈10nm for these dislocations when contained in {10 1 0) planes; this difference in separation serves to illustrate the anisotropy of antiphase boundary energy in the compound.