Microstructure control of TiAl alloys containing β stabilizers by directional solidification

Dependency of microstructure and microhardness on withdrawal rate of Ti-43Al-2Cr-2Nb alloy prepared by electromagnetic cold crucible directional solidification

“…After directional solidification, the oxygen content of ingots was measured with a LECO TC-436 N/O apparatus as described in Ref. [7,9]. The test results of the oxygen content were lower than 380 wt.…”

“…This is mainly attributed to the increase of B2 and α 2 phases as well as the refinement of lamellae. ductility when the lamellar boundary orientation was parallel or inclined to the loading axis [6,7] . During the past two decades, extensive directional solidification experiments were carried out to achieve columnar grain with preferred lamellar orientation [8,9] .…”

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

“…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.…”

“…The other method to control lamellar orientation was generally performed with a ram type DS furnace. 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] .…”

“…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. In order to clarify the characteristic of lamellar orientations under higher temperature gradient, the liquid metal cooling type DS apparatus was selected in the study.…”