The microstructures of Ti47Al8NbxMn (mole fraction, %) alloy with x=1 or 2 were studied on as-cast, as-HIPped and on heat-treated samples. The results showed that Mn element is β phase stabilizer and promotes the for...The microstructures of Ti47Al8NbxMn (mole fraction, %) alloy with x=1 or 2 were studied on as-cast, as-HIPped and on heat-treated samples. The results showed that Mn element is β phase stabilizer and promotes the formation of β(B 2) phase. B 2 phase exists at the dendrite cores of the as-cast microstructures. This phase is metastable and can completely decompose into α and(or) γ during 1 200 ℃, 200 MPa, 4 h HIP process. In the as-HIPed alloy with 1% (mole fraction) Mn addition, the α 2+γ lamellae structure is interrupted and decomposed resulting in grain refined near gamma microstructure. The α 2+γ lamellae structure near interdendritic regions decomposes almost completely into γ grains, but near dendrite cores incompletely into γ grains with a small amount of α 2 particles or needles around or in it. However, compared with the alloy with 1% (mole fraction) Mn, more α 2 phase is retained in the alloy with 2% (mole fraction) Mn. α 2 phase contains more Mn and is more stable in the alloy with 2% (mole fraction) Mn than in that with 1%(mole fraction) Mn. This makes its grain refinement more difficult. The amount of α 2 phase decreases following (1 250 ℃, 7 h-1 150 ℃, 15 h) for 3 cycles heat treatment.展开更多
文摘The microstructures of Ti47Al8NbxMn (mole fraction, %) alloy with x=1 or 2 were studied on as-cast, as-HIPped and on heat-treated samples. The results showed that Mn element is β phase stabilizer and promotes the formation of β(B 2) phase. B 2 phase exists at the dendrite cores of the as-cast microstructures. This phase is metastable and can completely decompose into α and(or) γ during 1 200 ℃, 200 MPa, 4 h HIP process. In the as-HIPed alloy with 1% (mole fraction) Mn addition, the α 2+γ lamellae structure is interrupted and decomposed resulting in grain refined near gamma microstructure. The α 2+γ lamellae structure near interdendritic regions decomposes almost completely into γ grains, but near dendrite cores incompletely into γ grains with a small amount of α 2 particles or needles around or in it. However, compared with the alloy with 1% (mole fraction) Mn, more α 2 phase is retained in the alloy with 2% (mole fraction) Mn. α 2 phase contains more Mn and is more stable in the alloy with 2% (mole fraction) Mn than in that with 1%(mole fraction) Mn. This makes its grain refinement more difficult. The amount of α 2 phase decreases following (1 250 ℃, 7 h-1 150 ℃, 15 h) for 3 cycles heat treatment.
