Abstract
The stress required to activate twinning of the longitudinal <112¯]{111} system in the lamellar γ-TiAl phase of the alloy Ti-45Al-2Nb-2Mn (at.%)-0.8 vol.% TiB2 was measured at several temperatures up to 700 °C by in situ micropillar compression of soft mode oriented γ-TiAl/α2-Ti3Al lamellar stacks. The lamellae undergoing deformation twinning were identified by electron backscatter diffraction orientation mapping. In some cases, such lamellae were not constrained by domain or colony boundaries and longitudinal twinning was the only deformation mechanism observed based on digital image correlation strain maps. The resolved shear stress for such unconstrained twinning was found to increase monotonically with temperature from 25 °C to 700 °C. This is consistent with the stacking fault energy increasing with temperature as found in many metallic alloys, suggesting that the increased ease of deformation twinning at high temperature in bulk TiAl alloys is due to the increased ease with which the twinning shear can be accommodated by the neighbouring domains and lamellae with increasing temperature, rather than a thermal softening of the intrinsic twinning mechanism.
Highlights
Twinning in TiAl alloys is essential for sufficient ductility to be obtained [1]
The present study reports the first high temperature in situ scanning electron microscope (SEM) microcompression test of TiAl
The loading curves for a representative selection of the pillars from each temperature are given in Fig. 4, illustrating the variability in loading behaviour observed for differing F and temperature conditions
Summary
Twinning in TiAl alloys is essential for sufficient ductility to be obtained [1]. Twinning of the g-TiAl phase in dual-phase lamellarTiAl alloys is known to occur as both longitudinal and transverse modes of the same < 112f111g 1 system [2,3], where the twins shear either parallel or transversal to the interfacial planes, respectively. Twinning in TiAl alloys is essential for sufficient ductility to be obtained [1]. Twinning of the g-TiAl phase in dual-phase lamellar. TiAl alloys is known to occur as both longitudinal and transverse modes of the same < 112f111g 1 system [2,3], where the twins shear either parallel or transversal to the interfacial planes, respectively. Twinning is reported to operate more with increasing temperature in both equiaxed g-TiAl grains and lamellar colonies [3e5]. The ease of twinning in g-TiAl can be increased by reducing the Al content and alloying with Mn and Nb [3]. The onset of twinning requires the formation of a twin interface stacking fault [6]; in g-TiAl the stacking fault maintains nearest neighbour bonding and no shuffle is required for mechanical.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
