The effect of the applied strain range on fatigue cracking in lamellar TiAl alloy

Continuous low cycle fatigue behavior of a lamellar structured Ti-46.6Al-1.4Mn-2Mo (at.%) alloy was evaluated at the testing temperature of 800degreesC to investigate the effect of the applied strain range on fatigue cracking. It is observed that fatigue life is reduced with increasing applied strain range and the slope change of the Coffin-Manson plot is strongly related to the change of fatigue cracking mode from transgranular to intergranular with applied strain range. It is observed that the change of fatigue cracking mode cannot be explained by an environmental effect and a precipitation effect. In the present study, the alpha(2)-->gamma phase transformation phenomenon is observed and the experimental results clearly indicate that the phase transformation at the grain boundary is responsible for the change of fatigue cracking mode with applied strain range. This is confirmed by a low cycle fatigue test with an additionally heat-treated specimen in which a predominant gamma phase is formed at the grain boundary. (C) 2002 Elsevier Science BY All rights reserved.