Abstract
High-temperature fatigue crack propagation tests were conducted on Ti-34 wt% Al intermetallic compound with lamellar structure, in order to elucidate the effects of lamellar boundaries and creep on the resistance to translamellar cracking. The results obtained are summarized as follows. (1) Slow crack growth during fatigue is found to traverse the lamellae, and its rate is independent of whether the cracking direction is perpendicular to the lamellae or along them. (2) The fatigue crack propagation rate, d l /d N , at 1073 K is correlated well with the effective stress intensity factor range, Δ K eff . (3) The fatigue crack propagation rate at room temperature is little slower than that at 1073 K. (4) Under creep-fatigue conditions, the crack propagation exhibits a time-dependence and its rate per cycle, d l /d N , is governed by the creep J -integral range, Δ J c . (5) In transverse crack propagation, the d l /d N -Δ J c relationship is independent of the crack direction to the lamellar surface. (6) Compared with some heat-resisting steels and alloys, the resistance of the present TiAl to fatigue crack propagation is remarkably low at high levels of stress amplitude while the resistance to creep- fatigue crack propagation is almost the same.
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