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To understand the effect of alloy stoichiometry on the microstructural development and mechanical behavior of γ-TiAl- based materials, it is necessary to have a determination of the phase relationships for the TiAl alloy system near the γ phase field. Cast structures and phases of Ti-(43-47)Al-8Nb-(1-2)Mn (at%) alloys have been studied by using scanning electron microscope and X-ray diffraction. Their solidification path and microstructure development during the solidification were analyzed. The experimental results show that the alloys with different Al contents form different macrostructures and microstructural morphologies. This indi- cates that the solidification paths are different with different Al contents. The alloy with 43Al forms equiaxed grain structure, and the solidification path is as follows: L —? L+β —? β —? α+β —> α+β cores —> O2+γ+B2 cores. Whereas the alloy with 47Al forms colum- nar grain structure, and the solidification path is as follows: L —> L+β —? α+β+L —? α+γ+β cores —> tXj+γ+BZ cores. The p phase is their primary solid phase and can be retained to ambient temperature. The alloy with 43Al solidifies completely into β phase. The peritectic reactions L+P —> α and L+α-? γ appear when the Al content increases to 47Al.
To understand the effect of alloy stoichiometry on the microstructural development and mechanical behavior of γ-TiAl-based materials, it is necessary to have a determination of the phase relationships for the TiAl alloy system near the γ phase field. Cast structures and of Ti The solid results have been studied by using scanning electron microscopy and X-ray diffraction. The experimental results of the solidification path and microstructure development during the solidification were - (43-47) Al-8Nb- (1-2) Mn show that the alloys with different Al contents form different macrostructures and microstructural morphologies. This indi-cates that the solidification paths are different with different Al contents. The alloy with 43 Al forms equiaxed grain structure, and the solidification path is as follows: L -? Whereas the alloy with 47Al forms of colum-nar grain structure, and the solidification path is as follows: L + β -? Β -? Α + β -> α + β cores -> O2 + γ + B2 cores The p phase is their primary solid phase and can be retained to ambient temperature. The alloy with: L -> L + β -? Α + β + L -? Α + γ + β cores -> tXj + γ + BZ cores. 43Al solidifies completely into β phase. The peritectic reactions L + P -> α and L + α-? Γ appear when the Al content increases to 47Al.