The role of surface condition, residual stress and microstructure on pre-yield cracking in Ti44Al8Nb1B

Pre-yielding and pre-yield cracking in TiAl-based alloys

“…The tests were generally carried out on the as-machined samples, because it has been shown that the stress at which acoustic events are detected is not a sensitive function of surface preparation as explained in [13], where it was shown that the compressive stresses in machined surfaces limit the growth of machining-induced surface cracks and deep electro-polishing removes both the cracks and the region which contains these stresses. As noted below, some observations were carried out on samples which were hand polished and then deeply electropolished so that any cracks present could be observed using SEM.…”

Fatigue properties of TiAl alloys

“…This effect is attributed to changes in surface residual stresses and premature surface cracking. Wu et al [10], by using acoustic emission, have studied the onset of pre-yield cracking in a Ti-44Al-8Nb-1B alloy prepared with various surface conditions, corresponding with different levels of residual stresses. Such pre-yield cracking has been shown to give rise to premature fatigue failure.…”

Fractographic analysis of the crack growth in the Fe3Al based intermetallic alloy

“…The spark machining of the pre-crack could eventually introduce residual stresses changing the initial fracture behaviour [19]. However, owing to the relatively brittle character of iron aluminides, the fatigue pre-cracking was not appropriate and so the electro-erosion was used.…”