The significance of acoustic emission during stressing of TiAl-based alloys. Part 1: Detection of cracking during loading up in tension

Samples of fully lamellar Ti44Al8Nb1B and Ti44Al4Nb4Hf0.2Si have been teste d in tension at room temperature while they were interfaced to an acoustic emission system. The generation of acoustic signals, at stresses well below the 0.2% yield stress and at higher stresses, has been shown to be due to the formation of cracks within individual lamellar colonies. Data obtained in the micro-strain region in loading-unloading measurements confirmed that there is significant plastic flow at stresses 200 MPa below the 0.2% proof stress of 625 MPa, and it is inferred that this flow gives rise to the cra cking. The mechanism whereby such cracking occurs and the possible influenc e of these cracks on subsequent fatigue behaviour are discussed. (C) 2001 A cta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.