Analysis of local microstructure after shear creep deformation of a fine grained duplex γ-TiAl alloy
D. Peter, G. B. Viswanathan, A. Dlouhy, G. Eggeler.
Acta Materialia, 58, 6431-6443, (2010)
The present work characterizes the microstructure of a hot-extruded Ti–45Al–5Nb–0.2B–0.2C (at.%) alloy with a fine-grained duplex microstructure after shear creep deformation (temperature 1023 K; shear stress 175 MPa; shear deformation 20%). Diffraction contrast transmission electron microscopy (TEM) was performed to identify ordinary dislocations, superdislocations and twins. The microstructure observed in TEM is interpreted taking into account the contribution of the applied stress and coherency stresses to the overall local stress state. Two specific locations in the lamellar part of the microstructure were analyzed, where either twins or superdislocations provided c-component deformation in the L10 lattice of the γ phase. Lamellar γ grains can be in soft and hard orientations with respect to the resolved shear stress provided by the external load. The presence of twins can be rationalized by the superposition of the applied stress and local coherency stresses. The presence of superdislocations in hard γ grains represents indirect evidence for additional contributions to the local stress state associated with stress redistribution during creep.
Keyword(s): itanium aluminides; Shear creep deformation; Transmission electron microscopy; Dislocations; Twinning