Development of directionally solidified γ-TiAl structures

Induction melting of γ-TiAl in CaO crucibles

“…Gamma titanium aluminides are the most serious candidates to replace traditional steels and Fe or Ni-based superalloys for high temperature applications, mainly in those areas where the combination of high tensile properties, creep strength and corrosion resistance, associated with superior strength-to-weight ratio are important, and cost is not a crucial factor, like aeronautical, aerospace and military equipments [1][2][3].…”

Microstructure evolution of Ti-47Al-2Cr-2Nb alloy in the liquid-metal-cooling (LMC) directional-solidification process

“…Thus, the annihilation of the parallel lamellar orientation should not stem from the reduced temperature gradient, according to the idea of Saari. Moreover, Jung [14] suggested that using the liquid metal cooling or the floating zone type DS apparatus, the parallel lamellar orientation would grow stably to the end of DS ingot. However, the parallel lamellar orientation was not observed at the end position of the casting bars in the study.…”

“…Research on polysynthetically twinned (PST) crystals of TiAl-based alloys showed that a good combination of strength and ductility can be achieved when the lamellar plates aligned parallel to the loading axis [5,6] . Therefore, lamellar orientation control through seeding technique [6][7][8][9][10][11][12] or modifying the composition and processing conditions [13][14][15][16] during directional solidification (DS) process has been a promising method to enhance the performance of TiAl-based alloys recently.…”

“…Jung [13] proposed that the lamellar orientation in the columnar grain of the Ti-47Al-2W alloy was inclined with the angle 45° to growth direction in the latter apparatus. According to the results from the analogous DS furnace, a relatively high proportion of the lamellar orientation parallel to the growth direction near the bottoms of the cast bars and relatively high proportions of lamellar orientations with angled and normal to the growth direction near the tops of the cast bars is suggested in the Ti-47.5 Al-2W-0.5Si and Ti-46Al-2Mo-2Nb alloys by Sarri [14] . Therefore, Jung [13,14] et al deduced that the temperature gradient (TG) provided by the ram type DS furnace was lower (about 30-70 K/cm) and even decreased during the DS process, which could not provide enough energy for the stable growth of the parallel grains to the end of DS ingot.…”

Self-propagating high-temperature synthesis of titanium and nickel aluminides with additives

“…However, these characteristics are high only if intermetallic alloys have perfect microstructure and controlled chemical and phase composition. This in turn requires improving the available processes of their production and developing new ones which would combine advanced techniques, such as alloying, dynamic recrystallization in cyclic and mechanical thermal treatment, superplastic forming, introduction of finely distributed hardening phases (dispersed ceramic inclusions and fibers), and directional solidification [4][5][6][7][8][9][10][11].…”