Twin and twin intersection phenomena in a creep deformed microalloyed directionally solidified high Nb containing TiAl alloy

Abstract

• The combination of directional solidification and microalloying can significantly refine the columnar grains and homogenize the microstructure of TiAl alloy. • Compared with ternary TiAl alloy, the microalloying high-Nb TiAl alloy exhibits more superior creep property at 760 °C/275 MPa. • The decrease of stacking fault energy can promote the dislocation dissociation and the formation of deformation nanotwins. • Twin intersections will create more boundaries in the lamellar matrix, which will act as obstacles to dislocation movement. The creep behavior of a directionally solidified TiAl alloy with a high Nb content after microalloying by the addition of small amounts of W, Cr, and B elements was investigated by scanning electron microscopy and transmission electron microscopy. By means of directional solidification and microalloying, a TiAl alloy with a fine and uniform microstructure and continuous columnar crystals was obtained. High-density dislocations, deformation nanotwins, and twin intersections were observed in γ lamellae. The results show that, in comparison with the ternary TiAl alloy, the microalloyed high Nb containing TiAl alloy exhibited better creep properties at 760 °C and 275 MPa. The decrease in stacking fault energy can promote dislocation dissociation and the formation of deformation twins, and the twin intersections can hinder the movement of dislocation to enhance the creep performance of the TiAl alloy.