Low-cycle fatigue and deformation substructures in an engineering TiAl alloy

Complex investigation of deformation twinning in γ-TiAl by TEM and neutron diffraction

“…On contrary, the comparison with the material state at fracture showed that increase of amount of deformation twins during further cycling (from 2.5 cycles to fracture) is negligible. These observations are fully in accordance with neutron diffraction measurements and support hypothesis (Henaff and Gloanec, 2005;Gloanec et al, 2007) that initial hardening period is caused mainly due to the intensive deformation twinning during the first three to four cycles.…”

“…For running a higher number of cycles between measurements of neutron diffraction, a higher strain rate of 32 Â 10 À 5 s À 1 was used. No effect of the strain rate on the hardening/softening behaviour of the material has been observed, which is in a good agreement with the observations made by Gloanec et al (2007). However, it is important to note that a small shift (drop-downs) of measured data noticeable in the case of the hardening curve of 0.4% strain amplitude was caused by issues with the experimental setup.…”

“…This measurement was done on the same deformation rig as for all other samples but without collection of neutron diffraction pattern. Note that compared to the lamellar γ-TiAl tested by Gloanec et al (2007) the near γ-TiAl investigated in this study exhibits a slightly higher Young's modulus and a lower yield strength. Five cyclic experiments were performed with two strain amplitudes and various number of loops.…”

“…Recent investigations performed by Henaff and Gloanec (2005) (Gloanec et al, 2007) supported the hypothesis that room temperature hardening is related to the prevailing deformation mode governed by twinning which would at least delay the formation of the "vein-like" structure observed under conditions where the cyclic hardening is moderate. A similar idea, but from a different point of view, was presented by Kauffmann et al (2000) and Marketz et al (2002).…”

Fracture characteristics of γ-TiAl alloy with high Nb content under cyclic loading

“…Such a dislocation structure would strongly hinder the dislocation glide in the low-density dislocation regions and contribute to the early cyclic hardening. Gloanec et al and Berteaux et al [13,14] also had reported the experimental phenomena in their respective study. With increasing testing temperature the gliding dislocations were greatly activated.…”