High Nb–TiAl ingots with various boron levels (0, 0.2, 0.5, 0.7 and 1.0 at-) were investigated using annealing in a single α phase field for various lengths of time, and a coarse grained zone (CGZ) was observed when the boron content was greater than 0.5 at-. Scanning electron microscopy and transmission electron microscopy were used to study microstructural evolution and boride transformation. Experimental results show that the width of CGZ is closely related with the boron addition and the cooling rate. The formation mechanism is discussed for various nucleation behaviors of boride at the ingot scale during solidification caused by the temperature induced supercooling and the boron induced compositional supercooling, which lead to dissimilar pinning effects of borides at high temperature.
TetsuiT., ShindoK., KobayashiS. and TakeyamaM.: ‘A newly developed hot worked TiAl alloy for blades and structural components’, Scr. Mater., 2002, 47, 399–403. doi: 10.1016/S1359-6462(02)00158-6
5.
AppelF., BrossmannU., ChristophU., EggertS., JanschekP., LorenzU., MullauerJ., OehringM. and PaulJ. D. H.: ‘Recent progress in the development of gamma titanium aluminide alloys’, Adv. Eng. Mater., 2002, 2, 699–720. doi: 10.1002/1527-2648(200011)2:11<699::AID-ADEM699>3.0.CO;2-J
6.
ChenG. L., ZhangW. J., LiuZ. C., LiS. J., , ‘Microstructures and properties of high-Nb containing TiAl-base alloys’ ‘Proc. Conf. on ‘Gamma titanium aluminides’’, 371–380; 1999, Warrendale, PA, USA, TMS.
7.
LapinJ., OndrúšL. and NazmyM.: ‘Directional solidification of intermetallic Ti–46Al–2W–0.5Si alloy in alumina moulds’, Intermetallics, 2002, 10, 1019–1031. doi: 10.1016/S0966-9795(02)00119-X
8.
LinJ. P., ZhaoL. L., LiG. Y., ZhangL. Q., SongX. P., YeF. and ChenG. L.: ‘Effect of Nb on oxidation behavior of high Nb containing TiAl alloys’, Intermetallics, 2011, 19, 131–136. doi: 10.1016/j.intermet.2010.08.029
9.
LeeH. N., JohnsonD. R., InuiH., OhM. H., WeeD. M. and YamaguchiM.: ‘Microstructural control through seeding and directional solidification of TiAl alloys containing Mo and C’, Acta Mater., 2000, 48, 3221–3233. doi: 10.1016/S1359-6454(00)00123-3
10.
WisbeyA., SinghH., LucasK. and BrooksJ.: ‘Mechanical performance of extruded Ti-46Al-5Nb-1W titanium aluminide’, Mater. Sci. Technol., 2011, 27, 1059–1066. doi: 10.1179/1743284710Y.0000000018
11.
HuD., MeiJ. F., WickinsM. and HardingR. A.: ‘Microstructure and tensile properties of investment cast Ti-46Al-8Nb-1B alloy’, Scr. Mater., 2002, 47, 273–278. doi: 10.1016/S1359-6462(02)00140-9
12.
KimY. W.: ‘Gamma titanium aluminides: their status and future’, JOM, 1995, 47, 39–41. doi: 10.1007/BF03221229
13.
ChanK. S. and DavidsonD. L.: ‘Fatigue and fracture in lamellar TiAl alloys’, in ‘Proc. Conf. on ‘Structural intermetallics’’, (ed. DaroliaR.., 223–230; 1993, Champion, PA, USA, TMS.
14.
KimY. W. and DimidukD. M.: ‘Designing gamma TiAl alloys: fundamentals, strategy and production’, in ‘Proc. Conf. on ‘Structural intermetallics’’, (ed. NathalM. V.., 531–543; 1997, Warrendale, PA, USA, TMS.
15.
NadakudurY. N., ZhangD. L., GabbitasB. and ChiuY. L.: ‘Tensile properties and fracture behavior of an ultrafine grained Ti-47Al-2Cr(at-) alloy at room and elevated temperatures’, J. Mater. Sci., 2012, 47, 1223–1233. doi: 10.1007/s10853-011-5887-8
16.
LarsonD. J., LiuC. T. and MillerM. K.: ‘Tungsten segregation in α2+γ titanium aluminides’, Intermetallics, 1997, 5, 497–500. doi: 10.1016/S0966-9795(97)00026-5
17.
HymanM. E., McculloughC., ValenciaJ. J., LeviC. G. and MehrabianR.: ‘Microstructure evolution in TiAl alloys with B additions: conventional solidification’, Metall. Mater. Trans. A, 1989, 20A, 1847–1895. doi: 10.1007/BF02663215
18.
HymanM. E., McculloughC., LeviC. G. and MehrabianR.: ‘Evolution of boride morphologies in TiAl-B alloys’, Metall. Mater. Trans. A, 1991, 22A, 1647–1662. doi: 10.1007/BF02667377
19.
KitkamthornU., ZhangL. C. and AindowM.: ‘The structure of ribbon borides in a Ti-44Al-4Nb-4Zr-1B alloy’, Intermetallics, 2006, 14, 759–769. doi: 10.1016/j.intermet.2005.11.013
20.
LarsenD. E.: ‘Intermetallic matrix composites. Materials Research Society Symposium Proceedings, Vol. 194, Effect of XD TiB2 volume fraction on the microstructure of a cast near gamma titanium aluminide alloy’, (ed. AntonD. L., McMeekingR., MiracleD. and MartinP.., 285–292; 1990, Pittsburgh, PA, Materials Research Society.
21.
GodfreyA. B. and LorettoM. H.: ‘The nature of complex precipitates associated with the addition of boron to a γ-based titanium aluminide’, Intermetallics, 1996, 4, 47–53. doi: 10.1016/0966-9795(95)00017-S
22.
ChengT. T.: ‘The mechanism of grain refinement in TiAl alloys by boron addition –an alternative hypothesis’, Intermetallics, 2000, 8, 29–37. doi: 10.1016/S0966-9795(99)00063-1
23.
EikenJ., ApelM., WitusiewiczV. T., ZollingerJ. and HechtU.: ‘Interplay between α (Ti) nucleation and growth during peritectic solidification investigated by phase-field simulations’, J. Phys. Condens. Matter, 2009, 21, 464104. doi: 10.1088/0953-8984/21/46/464104
24.
GosslarD., HartigC., GuntherR., HechtU. and BormannR.: ‘Heterogeneous nucleation and growth of the β (Ti) phase in the Ti-Al system – experiments and model calculations’, J. Phys. Condens. Matter, 2009, 21, 464111. doi: 10.1088/0953-8984/21/46/464111
25.
HechtU., WitusiewiczV., DrevermannA. and ZollingerJ.: ‘Grain refinement by low boron additions in niobium-rich TiAl-based alloys’, Intermetallics, 2008, 16, 969–978. doi: 10.1016/j.intermet.2008.04.019
ImayevR. M., ImayevV. M., OehringM. and AppelF.: ‘Alloy design concepts for refined gamma titanium aluminide based alloys’, Intermetallics, 2007, 15, 451–460. doi: 10.1016/j.intermet.2006.05.003
28.
HuD., YangC., HuangA., DixonM. and HechtU.: ‘Solidification and grain refinement in Ti45Al2Mn2Nb1B’, Intermetallics, 2012, 22, 68–76. doi: 10.1016/j.intermet.2011.11.003
29.
HuD., YangC., HuangA., DixonM. and HechtU.: ‘Grain refinement in beta-solidifying Ti44Al8Nb1B’, Intermetallics, 2012, 23, 49–56. doi: 10.1016/j.intermet.2011.12.022
30.
DingX. F., LinJ. P., ZhangL. Q., SuY. Q. and ChenG. L.: ‘Microstructural control of TiAl-Nb alloys by directional solidification’, Acta Mater., 2012, 60, 498–506. doi: 10.1016/j.actamat.2011.10.009
