TY - GEN
T1 - Effect of Nb on lamellar orientation control of single crystal gamma TiAl alloys with fully lamellar microstructure
AU - Takeyama, Masao
AU - Yamamoto, Yukinori
AU - Nagaki, Masato
AU - Hashimoto, Kiyoshi
AU - Matsuo, Takashi
PY - 2004
Y1 - 2004
N2 - Lamellar orientation control of Ti-48Al-8Nb unidirectionally solidified using a seed of γ single phase Ti-57Al single crystal has been examined by electron backscatter diffraction (EBSD), and the results are compared with those of binary Ti-48Al grown crystal. Both alloys become single crystal with fully lamellar microstructure (PST), although several lamellar grains are formed above the seed crystal. While the binary PST crystal does not always follow the seed orientation, the ternary grown crystals always follow the seed orientation with <11̄0]γ direction parallel to that of the seed. Addition of Nb improves the fitness of the lattice parameters between the grown and seed crystals, and also suppresses the peritectic reaction (L+α→γ). The liquidus projection in Ti-Al-Nb ternary system is calculated based on lattice stability of β-Ti, α-Ti, γ-TiAl and liquid phases, and it is found that the alloys with compositions to be a solidification in average by mixture of the seed composition could follow the seed orientation. Addition of Nb drastically decreases the fraction of energetically unstable variant interfaces, thereby stabilizing the lamellar microstructure at elevated temperatures.
AB - Lamellar orientation control of Ti-48Al-8Nb unidirectionally solidified using a seed of γ single phase Ti-57Al single crystal has been examined by electron backscatter diffraction (EBSD), and the results are compared with those of binary Ti-48Al grown crystal. Both alloys become single crystal with fully lamellar microstructure (PST), although several lamellar grains are formed above the seed crystal. While the binary PST crystal does not always follow the seed orientation, the ternary grown crystals always follow the seed orientation with <11̄0]γ direction parallel to that of the seed. Addition of Nb improves the fitness of the lattice parameters between the grown and seed crystals, and also suppresses the peritectic reaction (L+α→γ). The liquidus projection in Ti-Al-Nb ternary system is calculated based on lattice stability of β-Ti, α-Ti, γ-TiAl and liquid phases, and it is found that the alloys with compositions to be a solidification in average by mixture of the seed composition could follow the seed orientation. Addition of Nb drastically decreases the fraction of energetically unstable variant interfaces, thereby stabilizing the lamellar microstructure at elevated temperatures.
KW - EBSD analysis
KW - Lamellar orientation control
KW - Lattice stability
KW - Liquidas surface of Ti-Al-Nb system
KW - Thermal stability of lamellar microstructure
KW - Unidirectional solidification
UR - http://www.scopus.com/inward/record.url?scp=18944387354&partnerID=8YFLogxK
M3 - Conference contribution
AN - SCOPUS:18944387354
SN - 0873395751
T3 - Proceedings of the International Symposium on Niobium for High Temperature Applications
SP - 253
EP - 265
BT - Niobium for High Temperature Applications - Proceedings of the International Symposium on Niobium for High Temperature Applications
A2 - Kim, Y.W.
A2 - Carneiro, T.
T2 - International Symposium on Niobium for High Temperature Applications
Y2 - 1 December 2003 through 3 December 2003
ER -